BEST MANAGEMENT PRACTICES (BMPs) FOR A SUCCESSFUL STUD FARM

BEST MANAGEMENT PRACTICES (BMPs) FOR A SUCCESSFUL STUD FARM

 

GENERAL PROCEDURES

Weight and condition

Regular recording of the weight of stallions, mares and foals should be performed on the stud. The ideal is to maintain the animals in a good (but not overweight) body condition that takes account of their production. Production for a stallion is considerably different in nutritional demand from that of a pregnant, lactating mare or young growing foal.

The body score system can be used in addition to the weight; the ideal adult body condition score should remain between 4 and 6 (on a scale of 10).

Foot care

Routine foot care by a skilled farrier is essential for adult breeding animals and foals. Brood mares can easily be forgotten during the busiest times of the year. Minor corrective measures can be taken to control limb deviations (angular and flexural) in foals either by careful rasping of the foot or by the application of surgical shoes with extensions.

Dental care

Dental examinations must be performed at least at 6-monthly intervals in older breeding stock (particularly stallions). Routine dental procedures include:

• Examination of the whole mouth using a gag and a suitable light source; it is best to use a head light during this examination.
• Rasping (‘floating’) of sharp enamel edges.
• Corrective dentistry such as hook removal or extractions. These procedures are described in standard texts.²

Identification procedures

One of the most essential aspects of stud farm management is the effective identification of mares, particularly those visiting animals that are not well known to the stud staff. Unfortunately, this is an area that is sometimes neglected and can then cause considerable problems.

There are a number of effective means of identification, each with some advantages and some disadvantages. Failure to identify a mare correctly at a stud can have catastrophic financial implications. Stallions are usually relatively simple to identify because they are generally managed in an individual fashion, whereas the mare population on a stud may vary markedly.

The methods available for identification of the animals include several visible means, some hidden means and some that rely on documentation. Most of the effective methods are permanent, but temporary identification can be useful under some conditions (e.g. short-term movement to a stud farm).

Hoof branding

Hoof branding (Fig. 3.1) is a semi-permanent method of identification, but of course the marks are lost as the hoof grows out. Also, it is possible to tamper with the marks by altering the figures to some extent. Nevertheless, it is a reasonably effective way that is painless (hopefully) and will certainly be identifiable for some 4–6 months. It can be repeated as many times as necessary.

FIG. 3.1 A hoof brand.

Usually a postcode/zipcode or telephone number is used, which can be spread over all four hooves.

What does it involve?

A red-hot iron is applied briefly to the hoof capsule to create an easily identifiable mark. Usually a combination of numbers or letters is used.

Advantages

• Reasonable duration of marking (it usually takes at least 4–6 months to grow out completely).
• Painless.
• Quick.
• Cheap.
• Difficult if not impossible to delete, but can be altered.

Disadvantages

• Temporary. It relies on some identification held elsewhere (e.g. at the owner’s home address: postcode/zipcode or telephone number).
• Possibly alterable within limits.
• Needs to be repeated as required.

Tattoo (lip/gum or ear)

A tattoo is a recognized way of identifying horses that relies upon the ancient art of permanent skin coloring. Usually the tattoo is applied to the soft pink lining of the inside of the lip. This enables the dark-colored pigment to be easily recognized. The shape of the lip, however, makes it difficult to apply the tattoo with a consistent degree of accuracy and so experience is required.

What does it involve?

A needle punch is loaded with stencils of an appropriate number/letter configuration and then the skin is wiped with the ink. Clamping the punch onto the lip (or ear, or gums) drives the needles into the mucous membrane (or skin). This carries a small amount of the ink into the skin and this remains as a permanent colored ‘scar’. The color of the ink can be altered but invariably it is much more difficult to see when it is applied to the skin rather than on the pink mucosal surface of the inside of the upper or lower lip.

Advantages

• Clear, permanent and definite.
• Little specialist equipment needed (often Indian ink is used).
• Cheap.
• Very difficult to erase/tamper with.

Disadvantages

• Painful.
• Messy.
• Not visible from a distance.
• Not easily visible in dark skin.
• Liable to be irregular (not every needle takes in the same amount of dye and some foci will not take up the dye).
• Many are difficult to read accurately.

Freeze marking

Freeze marking (Fig. 3.2) has been used for many years as a means of identification. It relies upon the change in color of the hair from body color to white when the skin is subjected to a defined cycle of freezing. The freezing is not enough, however, to cause serious freezing leading to ulceration of the skin. In gray horses the method requires a harder freeze because the intention is to create a hairless mark rather than just a change in the color of the hair coat. A white mark on a white-haired horse would probably not be obvious! In many cases the freeze mark is not very obvious until the area is clipped, but most freeze marks are obvious from a distance.

FIG. 3.2 (A) A freeze brand. (B) A freeze brand can suggest both identity and a possible insurance history.

What does it involve?

This is a simple procedure that is usually performed without the need for sedation. It is seldom if ever uncomfortable for the horse; most just continue to eat while it is being done. The technicians who are skilled at doing the procedure have a standard freeze protocol for gray and nongray horses. Usually an obvious site is chosen. The procedure involves clipping and removal of an area of hair where the brand is to be placed, spraying the area with 70% alcohol and applying the chilled brand (the brand is placed in liquid nitrogen until ‘boiling’ ceases) to the area of application. Foals require 10–12 seconds of contact, yearlings 15–18 seconds, adults 20–25 seconds. These times can vary if incorrect brands are used.

Advantages

• Simple method.
• Painless.
• Cheap.
• Definite; no scope for tampering.
• Visible from a distance (thieves will be less inclined to steal a horse with a visible freeze mark).

Disadvantages

• Requires a skilled technician.
• Loss of cosmetic appearance due to presence of numbers.
• Not always clearly visible (differences in gray horses).

Hot branding

Hot branding (Fig. 3.3) commonly takes two forms. The first is a standard identification mark that is used for specific breeds of horse. The second is some form of specific identification; historically, this was used to identify the owner of the horse or its origin, but it could equally be used to add numbers and letters in combination so that the animal can be identified permanently. The brand is usually applied at an early age (when restraint is more practicable). The effect is obtained by creating an obvious, defined shaped scar. No hair grows on the scar and it is therefore visible from a distance and regardless of the hair coat status (winter/summer).

FIG. 3.3 This example of a hot brand simply identifies a breed or type.

What does it involve?

The brand is invariably applied by a red-hot iron, either as a single preformed ‘trade mark’ or as a series of numbers/letters. The resultant burn causes scarring of the skin and hair loss over the area. The scar is usually black and thinner than the normal skin. Some operators will try to use a lower temperature and create a lesser scar. Over the passage of time the scar may become distorted and so may be less recognizable. Hot branding is no longer permitted in some circumstances (e.g. in Thoroughbred and Standardbred horses in Australia and New Zealand).

Advantages

• Permanent markings are easily identified as being applied on purpose rather than as accidental scars.
• Categorical identification should be possible.
• Little opportunity for tampering with them.

Disadvantages

• Very painful, rather brutal, procedure.
• Causes significant skin destruction.
• Scars can distort over time and will in any case inevitably shrink, making the mark less clear.
• ‘Lightly’ branded horses may be impossible to identify accurately by the brand.

Microchip identification

Microchip identification of horses is gaining much credibility as more and more chips become available and more and more microchip readers are held by police, slaughter houses, customs, and welfare and charitable institutions. Although there are the usual horror stories of nasty injection reactions and migrating chips, these are extremely rare; indeed, they may be less common than physical injury to the exact site of the chip placement.

What does it involve?

The procedure is relatively simple with a single subcutaneous injection, usually on the side of the neck. The procedure is usually (but not always) virtually painless.

Advantages

• Definite.
• Permanent.
• Tamper-proof.
• Minor cost.
• Little pain involved in insertion.
• Can be read from a distance with the appropriate reader gun (e.g. from outside a truck or by a reader placed by the roadside during an event).

Disadvantages

• Invasive procedure.
• Invisible.
• May move/migrate.
• The occasional horse may require sedation or twitching.
• Occasional abscess formation with loss of chip.
• Detection relies on possession of a ‘reader’.
• Reader must be passed over the chip.
• Not all readers read all chips.

Identification by natural markings/scars (permanent alterations)

This has been used for many years as a means of categorical identification. It relies upon the accurate and detailed sketching and written description of all naturally occurring white marks and hair whorls. Often it includes certain permanent acquired markings.

What does it involve?

A written description and a sketch that corresponds exactly have considerable advantages in that there should be no debate thereafter that the horse is the one described. However, it does rely on a suitable piece of paper/document and this is not always filled in completely or legibly. Furthermore, after regular handling the document may become difficult to read. A passport that contains a photocopy of the original identifies Thoroughbred horses and certain other breeds. This is over-stamped to ensure that there is no possibility of tampering with the sketch or the narrative.

Advantages

• Usually completed by a veterinary surgeon with a signature to support its veracity.
• Text and sketch should correspond exactly making tampering difficult/impossible.

Disadvantages

• A very time-consuming, and therefore expensive, procedure if performed properly by a veterinary surgeon. Most breed societies will only accept certificates of identification if they are signed by a veterinary surgeon.
• The passport or ID form is required for comparison.
• Open to abuse if blank forms fall into the wrong hands. Forged signatures and false sketches and narratives are easy to prepare.
• Some difficulties with colors, especially in bay/chestnut foals that subsequently turn gray.

Photographic identification

Photographic identification has not gained the reputation or universal application it perhaps deserves. There is scope for the inclusion of color pictures in a sealed tamper-proof plastic sheath. However, photographic quality varies and in some cases it may not be helpful at all. For example, almost all Fell ponies are a very similar uniform color and so a photograph might not be helpful. Similarly, gray horses and Appaloosa horses will often not retain either the same color or the same pattern distribution. Some foals are born bay or chestnut and change to gray.

What does it involve?

A simple series of photographs taken from the left, right, front and rear with a close-up of the head will identify a horse definitively so long as the markings are obvious on the photographic plate.

Advantages

• Easy.
• Cheap.
• Very positive (color is exact).
• Cannot be tampered with (some exceptions with modern computer technology).

Disadvantages

• Lack of credibility with respect to the individual horse unless accompanied by a certificate of authenticity signed by a veterinary surgeon.
• Some breeds such as the Fell pony have few if any identification marks apart from whorls and these may be difficult/impossible to see on a photograph.
• Will depend heavily on photographic quality. In many cases it is impossible to see whorls or small marks/scars clearly.
• New scars or skin damage from injury, etc. may change the appearance significantly from that in the photograph.

Blood typing (gene/DNA mapping)

Blood typing is helpful in establishing parentage but on its own does not help to identify an individual horse.

Tissue typing can, in theory, be performed from any body tissue, including clippings, hair, blood, semen or even cells taken from the cheek lining. In practice, it is usual to use hair or blood. The tissues can be stored indefinitely and the technology is becoming more readily available and cheaper with advancing scientific methods.

The genetic make-up of the tissue cells of an individual is totally unique. However, gene mapping is really an advanced form of tissue typing and provides no more information than the tissue type with respect to identification.

What does it involve?

A single sample of a body tissue is all that is required. Commonly, this is frozen whole blood but could equally be hair or hoof clippings. Every cell and its remnants will carry the unique genetic code for that particular individual and this could (at least theoretically) be used to identify the original animal categorically for eternity.

Advantages

• Categorical method of identification.
• Permanent.

Disadvantages

• Invisible.
• Only applies when there is other tissue to compare it with (i.e. ‘is this my horse for which I have tail or mane hairs or a blood sample’).
• Expensive technology at present.

Vaccination

Routine vaccination is usually performed for a variety of diseases according to local disease-control requirements. For an effective immunologic response the animal needs to be healthy and have an active immune system. Stress, debility, illness or malnutrition can influence the response to a vaccine. All vaccines have a defined protocol that enhances the protective response in the vaccinated animal, but although most are regarded as beneficial some do have potential harmful effects and some are much less efficacious than others. Thus, the vaccine for tetanus is regarded as excellent protection whereas that for influenza can be less predictable. The nature of the disease and the organism itself has an influence on the efficacy of a vaccine.

Tetanus

In general, all horses are vaccinated routinely against tetanus using a standard routine. This involves a primary course of two intramuscular injections of tetanus toxoid followed by a booster vaccination after one year and then every alternate year.

Foals are usually considered to be effectively covered for up to 6–8 weeks of age through colostral transfer of antibody (see p. 374) provided that the mare received a booster vaccination in the last trimester of pregnancy. If a mare has not been vaccinated for between 1 and 2 years before foaling the duration of transferred immunity is probably inadequate.

If there is any doubt about either the effectiveness of the vaccination of the mare or the efficiency of colostral (passive) transfer of immunity (see p. 377) it is common practice to administer a single or repeated doses of between 1500 and 6000 IU of tetanus antiserum. This will usually confer effective protection for up to 12 weeks of age.³

The administration of a tetanus toxoid at, or shortly after, birth is controversial, but in theory at least there should be no particular problem with vaccination at 2–4 weeks of age.⁴ However, most authorities do not recommend vaccination at birth of a foal that has effective passive transfer on the basis that passive antibodies will interfere with active immunity for a primary vaccination. Repeated vaccination during this time may indeed result in poor long-term immunologic response to the vaccine, and in some cases there may be no effective response. However, some authorities consider that active vaccination in the face of passive maternal immunity is effective.⁵

Influenza

Vaccination against influenza viruses (equine influenza A, types 1 and 2) is common practice in most areas of the world. However, there are a few places where the disease does not appear to exist and vaccination is not practiced (e.g. Australia and New Zealand).

There are several different combinations of virus strains in commercial vaccines. The natural antigenic drift means that vaccination is not likely to confer certain and complete protection. Rather it serves to modify the course and severity of the infection. Vaccines are regularly up-dated to include the most recent strains so that the conferred immunity is as near to the field virus as possible.

Immunity to the adjuvanted vaccines is reported to be around 6–9 months, but the immune-stimulating complex vaccines provide protective antibody for 12–14 months.

Passive immunity is transferred to the foal via the colostrum and is probably protective for up to 6–8 weeks.

Primary vaccination for a foal is instigated at around 5–6 months of age. Vaccination is repeated at 30 and 150 days after the initial vaccination. Annual boosters are usually given, with stud mares receiving a booster some 3–5 weeks pre-term.

Equine herpesvirus 1 and 4 (rhinopneumonitis)

Infection with equine herpesvirus 1 is a serious cause of abortion, neurological disease in adult horses and neonatal death in foals. Vaccination has become more widely used since the quality of protection has improved. Infection with equine herpesvirus 4 is probably less serious but can cause abortion.

The vaccines do not appear to prevent the development of the neurological form of the disease.

There are three types of vaccine available:

• A killed oil-based vaccine that has been used for many years to prevent abortion. The vaccine is administered to pregnant mares at 3, 5 and 7 months of gestation. Stallions are vaccinated as for nonpregnant mares (i.e. by annual booster).
• Modified live virus vaccine. Although this vaccine does confer good immunity against both virus strains, it should not be used in pregnant mares.
• Killed bivalent vaccine with immune stimulating complex. These vaccines are widely available and are effective in controlling abortion as well as respiratory disease.

Usually three doses are administered at 3–4-week intervals with 6-monthly boosters thereafter, but individual vaccines may have particular requirements for the various classes of stud animals. It should be noted that for maximum protection all in-contact horses must be regularly vaccinated.

Equine viral arteritis

This disease causes abortion, infertility, upper respiratory tract disease and arteritis (see p. 259). It has a worldwide distribution, but some areas are free of the disease. Vaccines are effective in preventing the disease but do not result in the cure of an infected carrier stallion .

An annual booster dose is given to all breeding stock at least 3 weeks before breeding.

Responses to vaccination cannot be distinguished from natural infection, thus serological investigation should precede the vaccine. This ensures that carriers and potential carriers (usually stallions) will not be used for breeding unless proven to be clear of the disease.

Equine viral encephalitis

Various types of equine viral encephalitis are prevalent in different areas of the world but large areas are free of infection and so vaccination is not practiced.

Most types of encephalitis are spread by blood-feeding insects (usually mosquitoes and midges). The disease therefore tends to be seasonal, but can be spread by fomites (e.g. needles and blood products).

Vaccination is usually by an inactivated bivalent or trivalent vaccine and the conferred immunity from a primary course is probably less than 6–9 months.⁵ The first dose of vaccine for foals is usually administered at 4–6 months of age.

Rabies

Stud mares and stallions are probably not at major risk of rabies infection but vaccination is quite properly used in endemic areas where the horses are exposed to possible wildlife vectors.

The primary vaccination course is two doses given 3–4 weeks apart; seroconversion is then measured and vaccination repeated until a protective level is achieved. Annual or bi-annual boosters are usually given.

Passive immunity is probably conferred for 12 weeks but little is known about this.

African horse sickness

This disease is restricted to Africa and has a highly seasonal prevalence based upon the presence of the vector (Culicoides imicola).

 

BREEDING MANAGEMENT OF THE THOROUGHBRED STALLION

John V. Steiner^†, Norman W. Umphenour,

The stallion is perhaps the most important asset of a breeding operation. Therefore, the primary concern of the stallion manager should be to maintain the stallion’s health and to maximize the stallion’s reproductive capacity. To use the stallion to his maximum capability, the stallion manager must meet the basic needs of the stallion and must understand his behavioral patterns as well as his reproductive limitations. Having one mare who is a poor reproductive performer is unfortunate, but one poorly managed stallion can have a disastrous effect on a breeding program. Because of the impact that the stallions can have on the productivity of a farm, they are judged more critically and culled more extensively than the brood mares.

SELECTION OF STALLIONS

There are basically two criteria for selecting a stallion.¹ The first is that a stallion prospect be a horse that is recognizable. Trying to promote an unknown stallion in the modern Thoroughbred market is difficult. A horse without a pedigree or a good race record is not a stallion prospect.¹ In addition, a stallion prospect must have shown ability on the racetrack because the object is to produce future racehorses. Horses selected as stallions should be able to potentially improve the quality of their offspring in a breeding program. If the stallion passes on desirable traits to a large percentage of his offspring, he is fulfilling an important genetic role. The thoughtful selection of a stallion for a breeding program must take into consideration the goals that the breeding program is intended to achieve.

The selection criteria for a breeding stallion are based mainly on performance, conformation, and pedigree. Although the main purpose of the stallion is to breed and impregnate mares, in general, his reproductive potential is not considered.² Therefore, the stallion manager must implement procedures to increase the reproductive efficiency of any stallion regardless of his inherent fertility. The long-term effects on the reproductive performance of the offspring of subfertile stallions are potentially catastrophic.

GENERAL MANAGEMENT OF THE BREEDING STALLION

Feeding Program

A successful breeding program requires a sound feeding program. Feeding is still considered an art, and although a great deal of scientific knowledge has been gained in recent years, the stallion’s body condition should be evaluated on a regular basis and feeding adjustments made as needed. In general, the nutritional needs of a stallion during the breeding season do not appear to be different from his needs during maintenance.³ A slight increase in energy intake may be necessary or beneficial during the height of the breeding season; however, it is easy to overestimate the nutrients needed by a stallion at this time.³ Overfed and obese stallions are more common and of greater concern than underfed ones. A maintenance ration consists of enough balanced nutrients to support normal, basic bodily functions.⁴ Adequate pasture or good-quality hay can usually meet these requirements, and free access to trace mineralized salt and fresh water is also necessary. Grain as an energy supplement in cold weather or under certain stressful conditions may also be warranted. The stallion’s size, condition, activity, and temperament all play a role in his nutritional needs. Therefore, diets should be adjusted for individual stallions.

The healthy stallion consumes 2%–3% of his body weight daily. At least 50% of this should be in the form of roughage. Vitamin A plays an important part in reproduction.³ A severe deficiency of vitamin A can result in a decrease or cessation of sperm production.³ Leafy green forages generally supply adequate amounts of vitamin A. Contrary to popular belief, supplementation with vitamin A and E over National Research Council requirements does not improve reproductive performance of stallions. Stallions generally require 10% protein in their feed; younger stallions require 12%–14%. Obesity may adversely affect libido and mating ability. Therefore, the only dietary requirement for efficient sperm production and good breeding performance is a balanced diet that maintains the stallion at his optimum weight. There is no conclusive evidence of any nutrient that is able to increase sperm numbers or quality.

Exercise

Horses naturally are roaming and grazing animals. Therefore, exercise for stallions is an integral part of their management that affects their mental and reproductive well-being. This basic need for exercise is often ignored or underestimated, and nutrition and exercise go hand-in-hand. A stallion needs exercise to remain in good physical condition and to maintain a sharp mental attitude. Exercise can be provided in one of the following ways or in various combinations: (1) turn-out in paddock, (2) riding, (3) lunging, (4) treadmill, (5) swimming, or (6) mechanical walker.

In determining the type of exercise program, the stallion manager must consider the physical condition of the stallion as well as his temperament. Turn-out in a small, 1- to 2-acre paddock should be the least that is done to provide exercise for the stallion. If the horse is not very active outside or seems to be gaining weight, a more forced type of exercise may have to be provided, such as riding or lunging, to keep the horse fit and happy. In addition, lack of exercise may lead to vices such as weaving, stall walking, and cribbing.

The amount of exercise time must be tailored to the stallion’s personality. Free exercise in a paddock can last as long as 24 hours a day for some horses depending on the weather conditions. Others may do well with just 1–4 hours a day. Riding or driving in a jog cart should be at a slow canter or a jog for 1–2 miles a day. This exercise should be done 6 days a week depending on how easily the horse maintains his condition. The goal is to keep a stallion fit for the breeding shed, not the racetrack, so that he has a good attitude toward his daily duty of covering mares.

The personnel responsible for exercising stallions must be good horsemen or horsewomen so that overwork and injuries can be avoided. If soreness, lameness, or an attitude problem develops, the person responsible should be capable of detecting the problem. The exercise program must be discontinued and the stallion must be completely evaluated before continuing with any exercise.

Regardless of the type of exercise, the horse must have a positive attitude toward the routine. The form of exercise must be safe and minimize the chances of injury to the breeding stallion. Horses that have to go to the breeding shed several times a day must be kept as sound as possible because this may influence their attitude toward covering mares. For the exercise program to be effective, it must complement other aspects of the overall management of the horse (e.g., amount of turn-out, physical condition, and mental attitude).

PREVENTIVE MEDICINE

Preventive medicine should cover several areas of care for the overall well-being of the stallion. Foot care, dental care, vaccinations, and deworming should be performed in unison with the other management programs.

Parasite Control

A good parasite control program should incorporate the use of deworming agents and pasture management. Although there are few studies to evaluate the effect of antiparasitic drugs on stallion fertility, most drugs are considered safe unless stated to the contrary by the manufacturer. Regular pasture rotation and harrowing are also part of a parasite control program. Periodic fecal examination for parasite eggs is a good way to monitor the effectiveness of the control measures used. Stallions are generally dewormed every 60 days, with rotation between ivermectin, pyrantel pamoate, and fenbendazole.

Immunization Program

Vaccinations

Most stallions are isolated for 6 months of the year, but during the breeding season, which lasts approximately 5.5 months (150 days), they are exposed to mares from different farms and countries. Stallions used for dual-hemisphere breeding are at greater risk of contracting contagious diseases. Therefore, it is important that an organized vaccination program be considered. At breeding farms, mares come from several farms and different areas, as well as countries, into a central location for breeding. Not only does this put the stallions at risk, but any exposed mare is at risk of spreading disease to many boarding farms.

Breeding stallions should be vaccinated approximately 60 days before the breeding season. In that way, any fever that may occur does not adversely affect semen quality. Generally, most stallions in Kentucky are vaccinated in December against rabies, tetanus, influenza, rhinopneumonitis, botulism, and West Nile virus. Rhinopneumonitis and influenza vaccines are repeated every 2 months. In addition, equine viral arteritis vaccine is required for Thoroughbred stallions in Kentucky with a subsequent 28-day isolation period following vaccination. If appropriate, eastern and western encephalomyelitis vaccine and Potomac horse fever vaccine are generally given in the spring.

Hoof Care

Hoof care should be tailored to the individual stallion. Daily turn-out in a grassy area is conducive to good hoof quality and is another reason to keep stallions out in the paddock as much as possible. Hooves tend to become dryer and more brittle when stallions are kept in a stall, especially when stabled on wood shavings or sawdust.

In general, hooves are trimmed every 6–8 weeks. Some stallions with specific hoof problems may have to be shod. Whenever possible, stallions should not wear shoes because shoes tend to constrict and damage the hoof wall.

Dental Care

Dental examination is conducted routinely once or twice a year or whenever a dental or oral problem is suspected. Routine dental floating is carried out as dictated by the oral examinations. This ensures the proper use of feeds so that body condition is maintained and digestive upsets can be kept to a minimum.

ARTIFICIAL LIGHTING PROGRAM

Horses are considered to be long-day breeders. Reproductive function in the stallion is not arrested during the winter months as it is in most mares. However, certain seminal and hormonal characteristics and many aspects of sexual behavior are affected by day length. Testicular size and weight, daily sperm production, semen volume, hormonal concentrations, and libido are increased during the natural breeding season compared with the non-breeding season.

The breeding season of brood mares is accelerated with an artificial lighting program. Providing stallions with the same artificial lighting program as for mares (16 hours of total light beginning December 1) results in increased testicular size and increased sperm output early in the year (i.e., February).⁶ Thoroughbred stallions show distinct seasonal and age-related changes in most of the reproductive parameters studied, and the exposure of such stallions to increased photoperiod produced significant alterations in these changes.⁶ In non-lighted stallions in central Kentucky, testicular diameters increased between February and June in young and middle-age stallions. In lighted stallions, testicular diameters were smaller in June than in February or April. Changes in testicular diameter were seen only in young or middle-age stallions, not older stallions, when under light treatment.

Similarly, hormone concentrations are affected by artificial lighting programs. Increased artificial light exposure results in elevated testosterone in February in both young and middle-age stallions, but by March, testosterone decreases and is similar to December levels. This increase is generally short-lived because stallions become refractory to this light stimulation. If the majority of mares are to be bred in February and March (early breeding season), exposing stallions to light may be beneficial. This is not the usual case, however, and a lighting program may not be suitable because the largest number of mares in a stallion’s book are generally presented in April and May in the northern hemisphere. Under the stimulation of lights, as the breeding season progresses, testicular size regresses to near that of stallions exposed to only natural day length. Therefore, increased day length by means of an artificial lighting program causes stallions to “peak” earlier than they would have on their own.

 

ROUTINE MANAGEMENT AND CLINICAL EXAMINATION

ROUTINE MANAGEMENT OF THE NEWBORN AND NEONATAL FOAL

In performing the procedures below the groom or owner must balance the need to interfere with the possible disturbance that this creates. It is suggested that parameters described for the APGAR score (see p. 69) are first established to determine the well-being of the foal. Assuming those parameters are normal and the birth process is considered normal, and there are no obvious risk factors, routine management procedures can be followed.

NEWBORN (0–24 HOURS)

Umbilical care

• Ideally treatment should be initiated as soon as the cord has ruptured. This is because the stump is a very good portal of entry for bacteria into the bloodstream and until the foal has sucked colostrum it has no immunity to this infection.
• Ideally the navel should be immersed in a 0.5% solution of chlorhexidine (Fig. 4.1).¹Dilute 1 part 2% chlorhexidine solution with 3 parts sterile water for a 0.5% solution. It is the authors’ experience that, although this preparation does decrease the incidence of umbilical stump infection, the stumps remain moist for a relatively longer period of time compared with the typical iodine preparations owing to poor desiccant effects. Consequently, a new recipe is now recommended such that, for every 500 mL of the 0.5% chlorhexidine solution made up with sterile water, the final 60 mL of this is in fact surgical spirit.

FIGURE 4.1 Navel dipping in chlorhexidine solution.

• Dipping should be repeated every 6–8 hours for the first 24 hours. Spraying may potentially be a better method of application because the solution will be under mild pressure.
• The use of povidone iodine has been called into question.¹The greatest reduction in bacterial colonization of the umbilicus after dipping has been shown to be with chlorhexidine as opposed to povidone iodine/2% iodine solutions.
• Strong solutions of iodine or tincture of iodine can cause rapid desiccation of the umbilical stump and burning and necrosis of the surrounding skin. This predisposes to local infection and patent urachus.
• The usefulness of aerosol antibiotic sprays (oxytetracycline, etc.) is questionable. These do not dry the stump as quickly as other preparations and all the time the stump is moist it is more prone to infection. In addition, the antibiotics are bacteriostatic and, therefore, the antibacterial effects are probably poor and non-persistent. The antibiotic may not be effective against the organisms present (many significant Gram-negative bacteria including E. coliare tetracycline resistant). However, the incorporated purple dye is at least an indicator that some attention has been given to navel health!
• The usefulness of powder preparations is also questionable for similar reasons to the above but, in addition, the likelihood of powder penetrating into the natural crevices of the stump is poor and therefore some parts will remain a nidus for infection.

Prophylactic use of enemas

Meconium consists of digested amniotic fluid and cell debris. It is never passed in fetal life unless there is fetal distress. Most foals pass meconium within 4 hours’ postpartum, and by 24 to 48 hours milk dung appears. Meconium retention is more of a problem in colt foals than in fillies (see p. 249). Enemas are often given prophylactically to foals by clients, either before or after the first suck . The timing of administration can be argued either way and in practice appears to make very little difference.

FIGURE 4.2 (A) Fletcher’s enema; (B) giving an enema.

Before first suck:

• For:prophylaxis as soon as possible, more pressure in abdomen in recumbency vs standing so enema is more efficacious
• Against:foal is less amenable to handling, may disturb maternal bonding.

After first suck:

• For:doesn’t disturb maternal bonding
• Against:by this time prophylaxis is deemed unnecessary because the swallowing movement and swallowing stimulates strong peristalsis, and colostrum itself is a laxative.

The type of enema used is the most important factor (100 mL phosphate-buffered solution is ideal, e.g. Fletchers^®, Pharmax Ltd, Bexley, Kent, UK), and the amount of times it is given. It is important that a client knows to apply an enema only once and that if any foal continues to have problems then veterinary advice should be sought. (For treatment of meconium retention see p. 249.)

Supplementation of the newborn with colostrum

At birth the oral nutrient intake becomes the sole source of nutrition and the importance of colostral antibody transfer cannot be overstated. Colostrum quality of the dam should be checked (see p. 391). If the quality is poor (i.e. < 50 g/L, < 1.060 or < 20%) then supplementation with donor colostrum is advisable before the first suck to prevent failure or partial failure of passive transfer of immunity. A local donor mare is the most suitable owing to the presence of antibodies to specific antigens or infections that she has encountered in the local environment. Fresh colostrum is better than frozen owing to the denaturing of complement in the freezing process. The uptake of IgG is greater if the foal is allowed to suck from a bottle rather than being stomach tubed .

Note

• In the US routine early administration of colostrum is a practice used by many farms. Many farms follow the practice of milking the mare out and feeding the foal via a bottle before it has risen (see Fig. 9.6 on p. 461). Most foals will readily take a bottle at this time and 200–250 mL of colostrum can be consumed provided that the foal has a good suckle reflex at this time. Alternatively many stud farms administer 250–300 mL of good quality colostrum to newborn foals via stomach tube (see p. 460).
• Many practitioners and stud owners believe that artificial colostral feeding is essential for the health of the newborn foal. Amongst its perceived benefits are that colostrum provides energy to the foal, it may decrease bacterial translocation across the open gut and it is an important measure for encouraging passage of meconium.
• Foals receiving immediate colostrum may have a higher overall survival rate than those left to their own devices.
• Weak foals that are slow to rise are particularly at risk for infection and lack of energy. The early administration of colostrum would seem especially prudent in such cases.

Weighing and examination of placenta for abnormalities (see p. 43)

Unless the owner or stud groom is experienced with this procedure it is usually best for every placenta to be assessed by the veterinary surgeon. This could be performed during their visit to do a routine foal examination (see p. 69).

Weighing the foal

Foals should be weighed on day 1 postpartum and regular follow-up measurements made to ensure correct growth rate of each foal (see p. 20).

OVER 1 WEEK

Parasite control strategies

Worm control is one of the most important aspects of stud management. Failure to control parasitic infestation and pasture build-up renders all other stud procedures largely irrelevant. As in all equine management types, the main aim of control is to prevent transmission of infective stages via the pasture, especially during the summer months.

Reduction in infestation rates can be achieved by chemotherapeutic or managemental control methods.

Chemotherapeutic control

The use of anthelmintic drugs to suppress fecal egg output has been the mainstay of strongyle control on studs for many years. However, this strategy can no longer be totally relied upon and managemental control is also vitally important (see below).^2,3 Prophylactic use of anthelmintics usually involves giving the first dose at 6–10 weeks of age. If parasites are likely to be a problem treatment can begin at an earlier age. Anthelmintic treatment can be planned in three ways: as interval treatment, strategic treatment (based on seasonal transmission patterns), or targeted strategic treatment (based on individual fecal egg counts as well as seasonal transmission patterns).

• Interval dosing: this involves the administration of a specific drug at regular time intervals during the high risk summer grazing period.
• Strategic dosing: the use of anthelmintics at specific times of year to disrupt the seasonal cycle of transmission has been widely and effectively employed in farm animal practice. The seasonality of horse strongyles is well established so strategic dosing at turnout, in the middle of the grazing season and again in the autumn is a rational approach to parasite control.
• Targeted strategic dosing: strategic dosing targeted at animals with significant (> 200 eggs/gram) adult parasite burdens to suppress pasture contamination at critical times of the year.

Whatever the strategy employed, owners should be aware of the recommended minimum dosing interval for each anthelmintic and should not dose more frequently.

Note:

• In practice, many studs in Newmarket, UK, are starting anthelmintic therapy in foals at 1 week of age postpartum using ivermectin.
• Moxidectin should not be used in foals less than 4 months of age.

Managemental control

Simple management control measures should also be used to reduce transmission of the parasites to the young foals:

• avoidance of high stocking density and overgrazed pasture
• isolation of horses with high fecal egg counts
• reducing year-to-year transmission by controlled grazing and management practices including resting pasture
• avoidance of young/juvenile horses in the same fields as the foals
• reducing translation of parasites to pasture by regular removal of feces from the pasture, twice weekly is the suggested frequency.

Experimental studies have demonstrated that, when performed correctly, pasture hygiene is an extremely effective method of suppressing fecal egg counts in grazing horses.

Foot trimming

All foals should have a conformation assessment in the first week postpartum and suitable exercise regimens determined. Assuming correct conformation, the first foot shaping and trimming by a farrier will usually be required at about 1 month postpartum. If any limb deviations are apparent before this time it is wise for the feet to be balanced sooner. Regular farrier assessment should then be a matter of routine approximately every 4 to 6 weeks.

ROUTINE VETERINARY EXAMINATIONS AND PROCEDURES OF THE NEWBORN AND NEONATAL FOAL

Detailed examinations of a newborn foal are usually conducted within the first 3 days as a matter of routine to ensure the foal is healthy and to detect any congenital abnormalities and early signs of disease. Routine examinations are paramount because they allow identification of the high risk foal (see p. 60), enabling early diagnosis and intervention.⁴ Vital things to remember are:

• a foal is not a 50 kg horse
• changes occur rapidly – a normal foal can deteriorate within hours
• it is essential that the clinician is familiar with normal parameters and postpartum changes (see p. 65).

If money is not limited, on many major stud farms a veterinary surgeon will examine each newborn foal on each of the first 3 days of its life. This enables problems to be detected very early and various daily routine procedures may be carried out (e.g. prophylactic use of tetanus antitoxin and antibiotics; see below). However, veterinary examinations are necessarily expensive and therefore if a client cannot afford such an intensive prophylactic protocol the stud staff or owners can be trained to recognize the subtle signs of disease and then call for help as required.

Usually most clients prefer the middle ground and ask for a single routine health check to be performed, and the clinical examination is normally recommended when the foal reaches 18–24 hours of age. This usually falls on day 2 postpartum and coincides with the blood sampling for routine IgG estimation (see p. 9) and with most insurance requirements.

The following describes the veterinary procedures that are routinely carried out on the major stud farms during the first 3 days postpartum (clinicians restricted to a single visit on day 2 will obviously need to combine many of these procedures and prioritize those that are essential/affordable).

Day 1 procedures

1. Weighing and examination of placenta for abnormalities .
2. Clinical examination of the foal :

• history
• examination of environment
• examination of behavior
• examination of vital signs.

3. Tetanus antiserum administration: this is a routine procedure in almost all studs. However, if the mare is adequately vaccinated with tetanus toxoid in late pregnancy and colostral intake is good (serum IgG > 8 g/L) there will be adequate protection against tetanus in the neonate and, therefore, this can probably be left out.

The dose of tetanus antiserum (Tetanus Antitoxin Behring^®, Intervet Ltd, Bucks, UK) routinely used on many studs (regardless of the vaccination status of the mare) is 3000 i.u. subcutaneously given at or soon after birth. Higher doses (6000 i.u.) have been suggested,⁵ but in the field this high dose appears to be unnecessary.

Tetanus antitoxin administered at this time usually provides up to 4–6 weeks of circulating immunity to tetanus in foals.

4. Administration of prophylactic antibiotics: prophylactic antibiotic use in newborn foals is controversial. However, many British stud farms use antibiotics as a matter of routine in all foals born. Recently, practitioners in the US have also begun using routine postbirth antibiotic administration to foals.

Broad spectrum bactericidal drugs are preferred although a routine single injection of a ‘long-acting’ formulation of procaine penicillin (at 20 000 i.u./kg intramuscularly q 24 h) is commonly administered at birth or shortly afterwards. Given that most serious neonatal infections are Gram negative, penicillin would not seem to be the most appropriate choice of prophylactic antibiotic for newborn foals (this is effective only against Gram-positive organisms and there are many resistant bacteria). The occasional staphylococcal or streptococcal infection may be prevented by this. The common practice of a single dose of long-acting penicillin administered at birth is probably not useful and may be viewed as misuse of the antibiotic. However, many experienced clinicians report a benefit without significant problems. Potentiated sulfonamides are also often used at 20 mg/kg intramuscularly q 24 h. However, these injections can be painful and resented and a 12-hourly dose rate would be more therapeutic.

Note:

• The choice of antibiotics is a matter of clinical preference but it is probably irresponsible to use a single dose rather than a full 3–5-day course of a calculated therapeutic volume.
• The individual circumstances of the stud will probably influence the need for prophylactic antibiotic use; for example, large studs with transient populations and those with a history of disease will probably benefit most from them.
• High risk foals almost all receive antibiotics because there is a much higher incidence of neonatal sepsis in these. Administration of antibiotic should be given as early as possible (see section on prevention of septicemia in the newborn p. 76).

5. Early determination of IgG at 8–12 hours of age: early evidence for impending problems of failure of passive transfer can often be detected at this stage. However, many clinicians wait until peak serum IgG levels are obtained from 18 hours onwards, especially if financial restraints mean that only one routine visit to examine the foal is permitted.

Note:

• If there is any suspicion of a problem a full blood profile (see below) and a blood culture should be instigated immediately.
• In some high quality studs blood culture is routinely performed (using blood derived from the placental vessels immediately after birth of the foal).

Day 2 procedures

1. Similar to Day 1.
2. Antibiotics.
3. Assessment of conformation with regard to exercise program: conformation and limb assessment and recommendations are made for amount and frequency of exercise, recheck, corrective trimming, hoof trim, etc.
4. Blood samples for routine hematology and biochemistry: these include serum proteins, fibrinogen/serum amyloid A and IgG measurement. This will allow determination of any evidence of failure of passive transfer of immunity, neonatal isoerythrolysis, septicemia, prematurity, etc. Submission of blood for all these tests is an optional practice – if money is restricted the single most important test is for serum IgG levels (see p. 394).
5. Assessment of passive transfer of immunity(see p. 9): this is important because of the total reliance that the foal places on passively transferred immunity for the first 4–9 weeks of life.

The assessment of passive transfer is routine in stud practice. Serum IgG levels peak at approximately 18 hours and, therefore, most clinicians assess this immunity on day 2 postpartum. However, an earlier measurement can be performed on day 1 to allow earlier intervention of suspected problems.

Measurement of serum IgG levels is a compulsory procedure for all high risk foals and there is much merit in performing this routinely in all foals.

The methods available are described on page 394 but include:

(a) total protein estimation

(b) globulin estimation (by subtraction of albumin from total serum protein)

(c) protein electrophoresis

(d) zinc sulfate turbidity test

(e) latex agglutination

(f) ELISA/ SNAP test

(g) concentration immunoassay technology (CITE)

(h) immunoturbidity test

(i) radial-immunodiffusion (SRID)

(j) glutaraldehyde precipitation test.

Note: Routine use of plasma is indicated if there is failure of passive transfer .

Day 3 procedures

1. Physical activity/condition.
2. Antibiotics.
3. Conformation/exercise.
4. Insurance examination if required.

FURTHER ROUTINE VETERINARY PROCEDURES IN THE OLDER FOAL

Vaccination recommendations for protecting foals

Foals’ vaccination start times depend on their ability to respond to vaccination as well as their dam’s vaccination history. When deciding how to approach the use of vaccines in foals it is important to decide which one of the following is the most important goal or whether both are equally important:

1. to protect the foal and weanling against specific high risk infectious diseases that affect this age group and have the potential to cause significant disease, either directly or by predisposing to other secondary infections, or
2. to initiate primary immunization to protect against disease later in life.

Diseases of high risk to young foals but low risk to adults include rotavirus and, in some geographic areas only, botulism. For these diseases the best approach would be to:

• booster vaccinate the dam before foaling to maximize uniformity of passive transfer
• ensure good passive transfer of maternal antibodies
• introduce management practices to reduce exposure to the infectious agent
• vaccinate the foal if risk continues beyond first few months of life.

Diseases of moderate to high risk for weanlings and older horses but lower risk to young foals born to vaccinated mares include influenza, tetanus, EHV1, EHV4, strangles, and, in some geographic areas only, eastern equine encephalomyelitis (EEE). For these diseases the best approach is to:

• vaccinate the dam before foaling to maximize uniformity of passive transfer
• ensure good passive transfer of maternal antibodies
• start foal vaccination after the risk of maternal antibody interference is no longer present in most foals, as long as it has been ascertained that vaccination in the face of maternal antibodies does not impair the ability of foals to respond when vaccinated later in life
• introduce management practices to reduce exposure to the infectious agent while primary vaccination is being completed
• use three or more doses of vaccine in the primary series to improve the chances that foals that did not respond to earlier doses will respond when given additional doses later.

Recommendations for vaccination against specific diseases

These recommendations will probably require adjustments as more information becomes available. It is possible that, for some diseases, lack of a serologic response may correlate well with lack of protection, whereas for others this may not be the case. On the other hand, the presence of a serologic response may not correlate well with protection, as is frequently the case for respiratory tract pathogens. With the exception of the intranasally administered strangles vaccine (Pinnacle IN, Fort Dodge), the modified live virus EHV1 vaccine (Rhinomune, Pfizer), and the modified live virus EVA vaccine (Arvac, Fort Dodge), most commercially available vaccines are inactivated, adjuvanted and administered by intramuscular injection. As such, they are more likely to induce a systemic serologic response than either a cell-mediated immune response or local mucosal immunity.

Tetanus

Protection against tetanus appears to be mediated entirely by circulating antibodies and these antibodies are transferred well via colostrum.⁶ Limited and conflicting information is available in the literature regarding the potential for maternal antibody interference with vaccination. Based on available published results, primary vaccination of foals against tetanus is recommended at 4 to 6 months of age. Tetanus toxoid is considered to be a potent antigen, and it has been widely accepted that concurrent administration of tetanus toxoid and antitoxin at different sites does not interfere with the response to tetanus toxoid. Consequently, it has been assumed that maternal antibodies were unlikely to interfere with the response of foals to tetanus toxoid. However, recent studies indicate that the response of 3-month-old foals from vaccinated mares is substantially poorer than the response of 6-month-old foals and yearlings.⁹ In addition, these studies showed that levels of induced antitetanus antibodies were substantially higher after administration of a third dose of vaccine than after two doses of vaccine, even in older foals. Therefore, the following protocol would be recommended:

• Vaccinate the dam 4 to 6 weeks before foaling.
• Begin foal vaccination at 4–6 months of age.
• Administer three doses of tetanus toxoid in the primary series (4–6 weeks apart).
• Booster vaccinate at 12–24 month intervals.

Influenza

Influenza specific antibodies of the IgG subisotypes are passively transferred to foals via colostrum and inhibit their response to inactivated influenza vaccine.Conclusive evidence has shown that these colostral antibodies declined with a half-life of approximately 30–38 days.These workers also demonstrated that the majority of foals from vaccinated mares did not respond to inactivated adjuvanted vaccines administered at 3 months of age, whereas a higher proportion of 6-month-old foals responded if given three doses of influenza vaccine in the primary course. In recent years, further studies have documented the failure of a high proportion of foals from vaccinated mares to respond serologically to inactivated influenza vaccines administered at less than 6 months of age.Another important finding was reported by Cullinane and co-workers¹⁴ who found that a substantial number of foals vaccinated at less than 6 months of age not only failed to respond serologically to doses of vaccine administered in the primary course but also failed to respond to as many as six doses of vaccine administered over the next year, suggesting that early vaccination in the presence of maternal antibody had induced immunotolerance to influenza vaccines.

From these observations it is recommended that foals from vaccinated mares should not be vaccinated against influenza at less than 6 months of age and that three doses of vaccine are necessary in the primary series. Immunity following vaccination with conventional parenterally administered inactivated vaccines is short lived and is highly correlated with levels of circulating antibody directed against surface hemagglutinin antigens.¹⁵ With the possible exception of ISCOM vaccines, conventional vaccines have limited potential to induce cytotoxic T lymphocyte responses or nasal secretory IgA responses.

In conclusion, the current recommendations for vaccination against influenza using inactivated vaccines administered by intramuscular injection would be as follows:

• Maintain all horses on breeding farms on a program of booster vaccination against influenza at 4–6-month intervals.
• Booster vaccinate mares 4 to 6 weeks before foaling.
• Begin foal vaccination at 6 to 12 months of age using three or more doses in the primary series.
• Booster vaccinate young horses at 3–4-month intervals until they are 2 years of age if risk of infection remains high.
• Mature performance, show, and pleasure horses constantly exposed to potential infection should be booster vaccinated at 4–6-month intervals.

Equine herpesvirus1 and 4

The major concern with EHV1 infection is the prevention of EHV1 abortion in mares. The recommended protocol for use of approved inactivated vaccines is to vaccinate mares during the fifth, seventh and ninth months of every pregnancy.

Correlates for protection against EHV1 and EHV4 in foals and weanlings have been extensively investigated but are not yet clearly defined. No clear relationship exists between protection from EHV1 infection and levels of circulating antibody induced by vaccination or infection, but the duration and amount of virus shedding from the nasopharynx are reduced in animals with high levels of circulating antibody.As with other herpesviruses, mucosal immunity and cell-mediated responses probably play a role at least as important as circulating neutralizing antibodies in protection against EHV1 infection. Because EHV4 replication is largely confined to epithelial cells of the upper respiratory tract, it is likely that mucosal immunity is important in protection.

Specific antibodies to both EHV1 and EHV4 are transferred in colostrum. Field studies with modified live EHV1 vaccines indicate that colostral antibodies exert a profound inhibitory effect on serological responses to vaccination up to at least 5 months of age,¹⁹ although a cytotoxic cellular immune response to both EHV1 and EHV4 was induced.²⁰ Recent studies with different commercially available inactivated vaccines have shown that the majority of foals from EHV-vaccinated mares do not mount a detectable neutralizing antibody response to vaccines administered at 3 and 4 months of age, even when three doses are administered in the primary series.^17,18 An increased proportion of foals responded when vaccinated with a three-dose series starting at 5 or 6 months of age, but still a substantial number failed to seroconvert.

 

Management of the Pregnant Mare

OBJECTIVES

While studying the information covered in this chapter, the reader should attempt to:

■ Acquire a working understanding of procedures used to manage the pregnant and parturient mare.

■ Acquire a working understanding of procedures used to monitor fetal viability during gestation.

■ Acquire a working knowledge of the rationale and procedures for monitoring the mare for readiness for birth.

■ Acquire a working understanding of the birth process, including the three stages of labor.

■ Acquire a working knowledge of the events that occur in the early postpartum period in the healthy foaling mare.

Mares should be managed attentively during pregnancy to help ensure the birth of a strong healthy foal with no injury incurred by the dam. Maintaining the mare in good health, being familiar with the signs of impending parturition, and preparing a foaling environment conducive to mare and foal health increase the likelihood of a healthy foal. Although managerial programs are usually adapted to meet special needs of individual mares or owners, certain strategies and methodologies are universally applicable. This chapter discusses routine care of the pregnant mare, methods for monitoring fetal viability, preparation of the mare for foaling, and the physiologic events of parturition to provide background for managing the term mare and birth process.

LENGTH OF GESTATION

Average duration of gestation in the equine is 335 to 342 days. Occasionally, viable term foals can be born as early as 305 days of gestation, but foals born before 320 days of gestational age are typically premature and nonviable. Some authors define abortion as the expulsion of the fetus before day 300 of gestation and use the term prematurity to designate birth of an underdeveloped foal between days 300 and 320 of gestation. The reader should recognize that use of these precise days for definition purposes can be misleading because gestation length is so variable in the equine. Certainly, foals delivered at more than 320 days of gestation can fit other criteria used to describe prematurity. Dysmaturity, on the other hand, designates birth of a full-term but immature and often undersized foal.

The duration of gestation is sometimes exceedingly long, 360 days or more, with no untoward effects on the fetus or mare (i.e., the fetus is not oversized and is viable, and no increased risk of dystocia exists). These long gestational periods have been hypothesized to result from the ability of the equine conceptus to undergo a period of arrested development during the first 2 months of gestation and then reinitiate growth and development.

Seasonal effects on the duration of equine gestation are found, with mares due to foal in late winter and early spring carrying their foals approximately 5 to 10 days longer than mares that foal later in the breeding season (late spring or summer). This seasonal effect can partially negate efforts made to get mares pregnant early in the breeding season (February 15 or soon thereafter) and can be circumvented by exposing pregnant mares to artificial lighting regimens (beginning December 1) identical to those used to initiate early ovulatory estrus in nonpregnant mares. Exposure of pregnant mares to artificial lighting systems can reduce gestation length by an average of 10 days.

Other factors that may influence gestational length in mares include gender of the foal (males are carried slightly longer), maternal nutrition, and environmental stresses. Ingested toxins (e.g., ergot alkaloids in contaminated fescue grass or hay) may lengthen the duration of gestation.

PREVENTIVE HEALTHCARE

Vaccination of the Pregnant Mare

Preventive health measures recommended for pregnant mares include regular immunization for common infectious diseases. Immunization of the pregnant mare serves two purposes: protection of the dam (and gestating fetus) and eventual protection of the newborn foal. Two viruses—equine herpesvirus 1 (EHV-1) and equine arteritis virus (the agent of equine viral arteritis [EVA]—are of special concern to the pregnant mare because they can cause abortion or birth of infected live but severely compromised foals. Many infectious organisms can infect foals, which are compromised in the ability to develop a high level of their own immunity early in life. Immunoglobulins produced in response to vaccine antigens are too large for diffusion across the placental barrier; nevertheless, the antibodies should be concentrated in colostrum and thus are made available to the newborn foal at the time of nursing (i.e., before “gut closure,” generally by 24 hours of age). If protection of the foal is of foremost concern, booster vaccines should be administered approximately 4 to 6 weeks before the projected foaling date to optimize concentration of colostral immunoglobulins to be passively transferred to the foal.

Protection of newborn animals through maternal immunization has been widely practiced by the veterinary profession for many years . Although the rationale for vaccination of the pregnant dam to enhance concentration of specific immunoglobulins in colostrum is well understood, documentation of efficacy for this practice for many specific vaccines so used is often lacking. Potential problems associated with vaccination of the pregnant dam include the following: (1) the pregnant dam may not respond as well to immunization (humoral response may be downregulated during gestation), which could lessen the desirable immune response of the dam to vaccine antigens administered during pregnancy; (2) administration of numerous different vaccines, even when given as multivalent products, at the same time might lessen the dam’s ability to respond favorably to specific antigens (i.e., vaccine interference). Thus, some authors recommend administering no more than four vaccine antigens at one time and waiting for 2 to 4 weeks before other vaccine antigens are administered; and (3) passively acquired immunoglobulins can interfere with the growing neonate’s ability to respond favorably to primary immunization against certain pathogens (e.g., influenza).

BOX 9-1 

Prefoaling Vaccinations

8 months of gestation	Rotavirus
9 months of gestation	Rotavirus
10 months of gestation	Rotavirus Equine influenza Eastern and Western equine encephalitis West Nile virus Strangles (Streptococcus equi)Botulism

Note: When 10-month prefoaling vaccinations are given during a time when other vaccines are scheduled, be careful not to double-vaccinate.

Routine vaccination with inactivated vaccines directed at many antigens is accepted as safe for the pregnant mare. Adverse impacts on pregnancy have not been shown for modified live intranasally administered strangles or influenza vaccines or for the modified live EHV-1 vaccine. The recombinant West Nile virus (WNV) vaccine is also thought to be safe for pregnancy. However, modified live virus Venezuelan Equine Encephalitis (VEE) vaccines and live anthrax spore vaccines should not be used in pregnant mares.

Selection of vaccines for immunization of pregnant mares should depend on many factors, including expected exposure to the disease, economic constraints, and vaccine efficacy and safety. Immunization programs should be tailored to meet needs of individual mares or owner needs (e.g., management practices that increase exposure to infectious disease) and disease control measures used on farms where mares reside. Also, parenterally administered vaccines are generally best for use in the prepartum period because intranasally administered vaccines are less effective for stimulating high levels of immunoglobulin G (IgG), the immunoglobulin that is transferred in high concentrations into colostrum. For a more thorough discussion of vaccinations for broodmares (and foals), including potential benefits, problems, and risks, the reader is referred to Wilson (2005) and the AAEP website (www.aaep.org/vaccination_guidelines/htm).

Although not exhaustive, some specific considerations regarding vaccination of pregnant dams follow.

Equine Herpesvirus Abortion

Equine herpesvirus type 1 (EHV-1) is the herpesvirus associated with abortion. The virus has also been associated with perinatal foal death; rhinopneumonitis in foals, growing horses, and some adult horses; and encephalomyelitis in adult horses. The virus is distinct from EHV-4, which is the major cause of rhinopneumonitis in foals and is only rarely isolated from equine abortions.

EHV-1 infection is acquired via inhalation, with the virus attaching to, penetrating, and replicating in upper airway mucosal epithelial cells. If local immunity fails to overcome infection, the virus breaches the basement membrane to invade the lamina propria of the respiratory mucosa and infects T lymphocytes and endothelial cells. The resulting viremia disseminates virus throughout the body. Abortion is the result of ischemia consequent to vasculitis of uterine vessels that disrupt the uteroplacental barrier. Lymphocytes resident within the endometrium are also thought to potentially transfer virus directly to uterine endothelium and result in abortion. This latter mechanism has been proposed to explain abortion of single mares in a group and abortions that occur many weeks or months after viremia.

Viral latency also occurs with EHV-1 infection, with periodic reactivation of latent virus resulting in asymptomatic shedding from the respiratory tract that may result in infection of in-contact horses. If local immunity has waned, reinfection and viremia can recur, again placing the fetus at risk. Although vaccinations do not eliminate preexisting latent EHV-1 infections, if they stimulate sufficient local immunity to prevent shedding, transmission of virus to other in-contact animals may be prevented.

Vaccination timing and efficacy against EHV-1 abortion remains controversial. Pneumabort-K +1b (Wyeth Animal Health, Guelph, Ontario) is a killed-virus preparation approved for use to protect against EHV-1 abortions in mares, with administration recommended during the fifth, seventh, and ninth months of gestation. Nonpregnant mares that may come in contact with pregnant mares should have vaccine administered at the same time as pregnant mares. Rhinomune (Pfizer, Animal Health, New York, NY) is an attenuated live virus preparation approved for use in preventing respiratory disease caused by EHV-1. Although the product label makes no claim for provision of protection against abortion, it does state that no adverse reactions have been reported in pregnant mares vaccinated with this product and further recommends vaccination of pregnant mares after the second month of gestation and at 3-month intervals thereafter. Prestige II with Havlogen (Intervet/Schering-Plough Animal Health, Whitehouse Station, N.J.) is a killed-virus preparation that contains EHV-1, EHV-4, and equine influenza subtypes A1 and A2; the product label makes no claims concerning provision of protection against abortion. Prodigy (Intervet/Schering-Plough Animal Health, Whitehouse Station, N.J.) is a killed-virus preparation of EHV-1 labeled for the prevention of abortion. Vaccination with this product is recommended at the fifth, seventh and ninth months of gestation. Recommendations for frequency of administration of booster vaccines, although they vary with the product used, are notably at frequent intervals because herpesviruses typically do not stimulate long-lasting immune protection (even immunity from natural infection wanes in 3 to 6 months). Although the efficacy of vaccination in the face of an abortion outbreak from rhinopneumonitis is unknown, Pneumabort-K +1b is labeled for this use.

Research regarding changing administration between vaccine types or brands during gestation is lacking. Some practitioners believe that switching vaccines during pregnancy leads to vaccine breaks in which EHV-1 abortion is more likely to occur. Until this phenomenon is studied, we caution against changing products during pregnancy in gestating mares.

Prevention and control of EHV-1 abortion cannot rely solely on a vaccination program because vaccination provides limited protection against viral shedding and the disease and properly vaccinated mares occasionally abort. One should use unerring management procedures in concert with a vaccination protocol to reduce mare exposure to the virus. Pregnant mares should be separated from the rest of the farm population. Permanent resident mares should not be allowed contact with transient boarders that normally reside elsewhere. Stress should be minimized to reduce the risk of activation of EHV-1 virus that may already be present in the mare. Mares that have aborted as a result of EHV-1 should be isolated from the rest of the herd. In addition, all mares that have been in contact with aborting mares should be segregated from those not yet exposed to the virus, and booster vaccines may be administered to in-contact mares in an attempt to stimulate immunity. Strict hygienic measures should be instituted to minimize spread of infection to the rest of the mares on the premises.

When facilities are limited for separating at-risk from nonexposed mares, the practitioner can perform polymerase chain reaction (PCR) testing on nasopharyngeal washes and whole blood samples collected from incoming mares. Procedures for nasopharyngeal washes are described by Conboy (2005). Submitting these samples to a diagnostic laboratory that can perform PCR testing for EHV-1 (e.g., University of Kentucky Livestock Disease Diagnostic Center, Lexington, Ky.) results in timely reporting of results, which can be used as a screening measure for either keeping animals isolated or allowing them to be moved into different locales on a farm. Animals with positive results on PCR testing of nasopharyngeal washes should at least be considered to have been exposed to the virus (but may not be actively infected, nor shedding the virus), and those with positive results in blood should be considered to be viremic and therefore likely to be shedding the virus. Some practitioners require maiden mares arriving at a breeding farm to be PCR negative for EHV-1 before they are allowed to mix with other mares at the farm or before they are allowed to be sent to a stud farm for breeding. Such a screening protocol may prove to be valuable in controlling an outbreak of EHV-1 respiratory or neurologic disease (although the test does not specifically identify the variant that causes neurologic disease).

Tetanus (Clostridium tetani)

Tetanus toxoid administration should be mandatory in all vaccination programs because of the incidence and life-threatening consequences of the disease for the dam and foal. The initial series of injections in unvaccinated horses consists of a two-dose series, with the second dose given 4 to 6 weeks after the first. For the pregnant broodmare, booster vaccines are given 4 to 6 weeks before the date of expected foaling to provide passive protection from colostrum intake by the newborn foal.

Encephalomyelitis (Sleeping Sickness)

This insect-transmitted neurologic disease is caused by viruses of the Togaviridae family, of which Eastern, Western, and Venezuelan encephalomyelitis viruses are most pathogenic. Horses in endemic areas should be immunized with a suitable inactivated-virus vaccine before the mosquito season each year, which corresponds to the foaling season. In areas where mosquito resurgence occurs in late summer or fall, a second annual dose should be given in late summer, just as for the inactivated WNV vaccine. Pregnant mares are routinely administered a booster vaccination 4 to 6 weeks before the date of expected foaling in an attempt to provide passive protection to the newborn foal from colostrum intake.

West Nile Virus

This insect-transmitted neurologic disease is also caused by a virus transmitted mainly by mosquitoes, and outbreaks have occurred throughout the United States and worldwide. Three vaccines are currently available for horses: (1) an inactivated vaccine that requires an initial two-dose primary immunization series; (2) a recombinant canarypox vaccine that requires an initial two-dose primary vaccination series; and (3) a flavivirus chimera vaccine that requires only a single dose for primary immunization. Revaccination in late summer before mosquito population resurgence has been recommended for both the inactivated and the recombinant products. All products are thought to be safe for vaccination of the pregnant mare, but recommendations have been to provide the primary course of vaccination to previously unvaccinated mares while they are nonpregnant. However, a recent Texas study revealed no adverse effects when the inactivated vaccine was administered to previously nonimmunized pregnant mares at all stages of gestation. Pregnant mares are routinely administered a booster vaccination 4 to 6 weeks before the date of expected foaling in an attempt to provide passive protection from colostrum intake by the newborn foal.

Rabies

The risk of rabies is widespread across the United States. Because of the associated mortality and public health risks, immunization against this disease should be recommended for all horses. A single dose is recommended for primary immunization. Pregnant mares can be administered a booster vaccination 4 to 6 weeks before foaling in an attempt to provide passive protection from colostrum intake by the newborn foal. However, because of the relatively long duration of immunity, some authors recommend the vaccine be given after foaling but before breeding to reduce the number of prepartum vaccines given to a mare.

Rotavirus Diarrhea

Rotavirus is considered to be the most common infectious cause of diarrhea in foals, and farm outbreaks can affect a large proportion of the foals on a farm and become endemic. Foals of very young age are susceptible to adverse effects of rotavirus infection, which causes a profuse watery diarrhea. One of the better ways to provide protection to newborn foals is to vaccinate pregnant broodmares. A three-dose series (1 month apart) of vaccine administration is recommended, with the first dose given at 8 months of gestation. Thus, the last dose is given approximately 1 month before foaling to optimize colostral immunoglobulin concentration.

Immunization against other infectious diseases is sometimes desirable, depending on local risk factors such as endemic diseases, housing in contact with horses of other ages, and contact with outside (nonresident) horses at risk of contracting transmissible infectious diseases such as influenza, strangles, botulism, anthrax, and Potomac horse fever. Product labels should be examined because some products (e.g., FluAvert IN, Intervet/Schering-Plough Animal Health, Whitehouse Station, NJ, and anthrax vaccine) caution against use in pregnant mares.

Protection against equine viral arteritis (EVA) may be necessary in some instances. Special precautions are needed for use of vaccine, and state and federal authorities may need to be contacted for approval of its use and guidelines for its administration. EVA vaccine (Arvac, [Guelph, Ontario] a modified live virus vaccine) was previously thought to be unsafe for administration to pregnant mares, but recent outbreaks of the disease in Quarter Horse populations throughout the Midwestern United States prompted its widespread use in pregnant mares, with no published adverse effects on fertility or already established pregnancies. Because of potential export restrictions, all horses to be vaccinated should first have seronegative status documented. Recommendations are for mares recently vaccinated to be kept segregated from other seronegative horses for a minimum of 2 to 3 weeks to prevent in-contact seronegative horses from seroconverting.

Dental Care and Parasite Control

Regular dental examination and floating enables proper grazing and chewing of feeds, which helps maintain body condition and prevent digestive upsets. The frequency of dentistry necessary depends on each individual mare’s dental conformation and wear but generally should be at 6- to 12-month intervals The goal of dental management is to ensure an ideal functional masticatory unit with regular filing and burring or cutting of teeth that are too long to balance the chewing surfaces from side to side and front to back. Sources of chewing discomfort should be identified and corrected.

Parasite control is second only to good nutrition in proper management. Discussion of the varied anthelmintics and programs for their use is beyond the scope of this chapter. However, three common methods of parasite control used for broodmares are (1) strategic dosing based on egg reappearance period (ERP); (2) regularly scheduled use of anthelmintics, performed at intervals (usually 2 or 3 months), with different chemical classes of dewormers in a rotating fashion in an attempt to avoid development of parasite resistance to products; and (3) continuous deworming, (e.g., daily feeding of Strongid C or Strongid C2X, Pfizer Animal Health New York, N.Y.). Any method should include twice-yearly (fall and spring) deworming with a product that removes bots (with use of a macrolytic lactone such as ivermectin or moxidectin) and tapeworms (with praziquantel). Deworming medications are generally considered safe for use during pregnancy unless otherwise indicated on the product label. A variety of dewormers are approved for use during pregnancy, including ivermectin, pyrantel pamoate, and pyrantel tartrate. Thiabendazole, fenbendazole, and piperazine have been used regularly throughout pregnancy with no known untoward effects. Cambendazole should not be used during the first 3 months of pregnancy. Always read the precautions on the package insert of anthelmintics before administering to pregnant mares.

Administration of ivermectin to the broodmare on the day of foaling is common practice to minimize the parasitic load of Strongyloides westeri. The infective larvae of this parasite are transmitted to the foal via nursing beginning about 4 days after birth.

Any deworming program should be suited to the individual requirements of a farm or stable, with evaluation of program success by examination of feces at regular intervals to monitor parasitic egg levels (eggs per gram [epg]). Sound pasture management (e.g., low stocking density, regular pasture rotation, and pasture harrowing) should be used in concert with deworming protocols to establish an effective antiparasitic program. An example of one health program, including a deworming schedule, for broodmares is presented in Box 9-2.

Box 9-2 

Example of a Herd Health Program for Pregnant Mares Used on a Thoroughbred Farm in Kentucky

January	Deworming (rotational) Equine rhinopneumonitis vaccine Equine influenza vaccine Streptococcus equi vaccine Botulism vaccine (if never received before, administer three doses in January, February, and March)
February	Rabies vaccine (before breeding)
March	Deworming (rotational) Equine rhinopneumonitis vaccine Eastern and Western equine encephalomyelitis vaccine Tetanus toxoid West Nile virus vaccine
April
May	Deworming (rotational) Equine rhinopneumonitis vaccine
June	Streptococcus equi vaccine
July	Deworming with praziquantel and ivermectin Equine rhinopneumonitis vaccine Equine influenza vaccine
August	Eastern and Western equine encephalitis vaccine West Nile virus vaccine
September	Deworming Equine rhinopneumonitis vaccine
October
November	Deworming with praziquantel and ivermectin Equine rhinopneumonitis vaccine
December

July and November dewormings include a product effective against bots and tapeworms.Note: To simplify scheduling of rhinopneumonitis vaccination, the vaccine is administered to every broodmare on the farm at 2-month intervals. Vaccination for equine influenza and Streptococcus equi (strangles) is twice yearly due to a summer-fall pregnant mare sales season. Because of mosquito resurgence, which typically occurs in the fall in this locale, a second late summer vaccination against sleeping sickness and West Nile virus is performed.

Nutritional Considerations

Proper nutritional support of the broodmare improves fertility and promotes normal growth and vigor of the developing fetus. The reader is referred to a review of nutrient requirements for gestating and lactating mares for a thorough discussion of feeding guidelines (Hintz, 1993). Pregnant mares should be kept in good body condition (body score of 6 to 7, based on a scoring system of 1 to 9). Best pregnancy rates are achieved in mares of good to fat condition. and fertility of thin mares is improved if they are gaining weight at the time of breeding. Because late gestation and early lactation place enormous metabolic demands on the mare and most are rebred within 1 month after foaling, broodmares should be in a positive energy balance at the time of parturition. However, mares should not be obese because obesity has been reported to be associated with birth of weak undersized foals. Specific nutrient requirements for gestating mares are available from the National Research Council (NRC) (1989). In general, three different feeding programs—energy, protein, and minerals—are necessary for pregnant mares, with dietary requirements dictated by lactational status and stage of gestation. Digestible energy (DE) requirements for mares during the first 8 months of gestation are the same as for maintenance and gradually increase during late gestation over the maintenance requirement (1.11, 1.13 and 1.20 times maintenance requirements for 9, 10, and 11 months of gestation, respectively). The additional maternal nutrition needed during the last 3 months of gestation is indicated because 60% to 65% of fetal growth occurs during this period. Because the growing fetus increasingly takes up abdominal space during this time, feeding of some grain and good-quality hay high in DE is necessary (perhaps as much as 0.5 to 1.0 kg grain and 1 to 1.5 kg hay per 100 kg of body weight). Initial body condition is important for optimizing fetal growth and mare lactation, so constant monitoring of body condition should be done to ensure dietary energy requirements are met.

Regarding dietary crude protein (CP) requirements, mares in late gestation need 44 g of CP per megacalorie (mcal) of DE. A rule of thumb is to provide 9% to 10% of the total ration (on a dry matter basis) as CP during the last 3 months gestation, as opposed to 7% to 8% CP in the total ration during the first 8 months of gestation (Hintz, 1993). Alfalfa hay is a good source of protein for pregnant and lactating mares.

DESIGN AND CONSTRUCTION OF A BREEDING FARM

Reg Pascoe and Woody Asbury

Although many breeders assert that a very good horse can only be bred in a few places in the world, horses are extremely adaptable and reproduce successfully in almost all regions and climates. In general, horses do well in both cold and hot climates. They tolerate high altitudes and deserts, flatlands and mountainous terrain. Furthermore, they reproduce in feral bands with no management at all in some countries.

It is unrealistic, therefore, to provide breeders with definitive directions for farm facilities, layouts and fencing that are suitable for any location. Moreover, it is probably too simplistic to prescribe definitive plans for the development of stud farms because there are so many possible variations. The basic concepts will apply in the majority of areas, and local information on building materials and methods will be utilized in the adaptation of these to local conditions. Also, it is recognized that ingenuity applied to management may be more important than defined structures that conform to accepted standards.¹ Use of good proven designs from existing facilities can often eliminate mistakes.

Climatic conditions and economic constraints have profound influences on the construction and management of the stud farm. The detailed requirements will vary markedly throughout the world. Although in some areas horses require to be stabled throughout the breeding season, in other areas this is not only undesirable but may be impractical. In areas without the rigors of periods of cold weather, drought and heat play a major role in the breeding industry and are significant factors in the running costs. As a general philosophy for horse management, horses are healthier when they spend longer outside. Clearly, however, the management and the quality of the pastures, paddocks and fencing will have a profound influence on the best circumstances under any particular conditions. Larger holdings with more equitable weather lead to fewer farm personnel being required than for the labor-intensive housing in barns in the winters of the northern hemisphere.

In planning and developing a facility to manage horses, safety for both the animals and their handlers must be a primary focus. In spite of the perception that there are more ways for a horse to injure itself than could ever be described, careful planning and management will prevent most avoidable injuries to both man and horse. A thorough understanding of equine behavior, careful thought about the procedures to be undertaken and focused concentration on the job at hand by the handlers should enable a stud to function safely and economically. Nevertheless, many facilities are adapted from previous farming facilities and here the dangers can be much higher. Before any detailed planning is started, and certainly before any building is undertaken, it is useful to visit as many other facilities as possible and discuss the advantages and disadvantages of individual systems.

The general outlines in this chapter apply to all horse-breeding areas in the world. Most countries have their own unique methods of handling, holding, feeding and rearing horses. However, there are many principles that can provide ideas for additional improvement and which may enhance the quality of the environment for horses.

Suggested references to broaden the reader’s scope appear at the end of this chapter. For the purposes of covering as many aspects of the subject as possible, it will be assumed that the reader intends to develop a breeding farm from the ground up. Realistically, many stud farms have been developed from existing agricultural facilities and this will inevitably introduce limitations of adaptation and difficulties of use that will need to be overcome. Obviously the purchase of a ‘turn-key’ facility changes the scenario, but the principles of sound, safe and efficient construction still apply and will influence that purchase.

FEATURES OF SUCCESSFUL FARM DESIGN

All farm designs should be aimed at ease of use and safety for the horses and their handlers. Problems are introduced by financial limitations, lack of understanding of the requirements of horse and handler safety, and the failure of some horse-management systems to take account of the fact that horses are living creatures, not just figures in a financial statement.

Hobby farms are seldom built to any recognizable standard of either economy or safety; frequently, they grow and adapt without conscious long-term design planning. Most restrictions are based upon financial considerations and where these are of no material concern it may be possible to construct the ideal facility for the specific place and time.

The management structures of commercial breeding farms are largely dictated by economic considerations, ease of management and safety aspects. There should always be contingency plans for expansion or recession. The investment in the land and all the subsequent developments must be put into context with the goals of the operation. In all but the most exceptional circumstances the economic aspects of the venture are also important. Hobby farms may not be subject to economic limitations and the biggest operations may also be run without regard for financial aspects. Most investors, however, are seeking some financial return or tax relief from their operation, if not always serious profits. Therefore, what is paid for the land, the level of property tax assessment and other operational costs are important. Furthermore, perhaps the most critical pressure is the appreciation potential of the property. Increasing population pressure exerts an upward pressure on land values. Should the horse-breeding venture be terminated, it would be some consolation to realize a gain from the investment in land and improvements. Careful planning at the outset should improve the chances of this.

Traditional approaches to housing mares and stallions were for two independent sets of quarters, isolated from each other to minimize excitement. However, recent equine behavioral research suggests that integrating stallions and mares in common facilities may have important benefits for the operation.² The so-called ‘harem effect’, resulting from interactions of sight and sound, produces a calming effect on both sexes, similar to the behavior of a band of mares running with a stallion. It is believed that both behavior and fertility are positively affected. No specific guidelines for facilities are offered, but the obvious first step is to house a stallion in a barn with mares.

Considerations of climate and local conditions are important in designing the farm and can significantly affect the layout. In subtropical regions, for example, housing requirements may be completely different from those in more temperate regions. The need for barn space will be significantly less if horses can remain outside all the time. Separation for feeding can be accomplished with small portable pens, or with simple ‘feeding barns’, which can double as holding spaces for routine examinations or extended day-length lighting systems (Fig. 1.1).

FIG. 1.1 An open barn ‘portable’ system of stables allowing easy access and good air hygiene.

SITE SELECTION

The selection of one type of site over another is based almost entirely on the prevailing climate. Before developing a farm in an unfamiliar area, it is important to consult with local agricultural extension services. Additional input from existing horse farm managers will also be helpful. The breeding records for particular areas may be helpful in establishing the best areas for horse breeding, but most established properties have adapted and altered their environmental features significantly over many years. Most breeders agree on the benefits of grass, whether it is naturally or artificially irrigated.

Horse farms are based on three types of space:

• Pastures watered exclusively by rainfall.
• Partially or supplementally irrigated pastures.
• Dry-lot areas in which there is effectively no pasture.
• For example, a desert property could be either irrigated pasture or dry-lot. The cost of water, an irrigation system and the labor to operate it would be significant factors in this decision. Commercial breeding farms usually opt for the dry-lot in this situation, providing forage with high-quality hay that can be grown efficiently where water is cheaper.

Water

Planning for water usage is critical to the consideration of a farm site. Regardless of its source, the quantity and quality of water are important and should be considered together with the potential to construct a reliable distribution system. Failure of free-choice water supplies, through prolonged subfreezing weather or extended droughts, for example, is potentially disastrous. In very cold climates the provision of warmed water is good management, and will spare labor in hauling bulk water. Brackish or salty water is usually poorly tolerated by horses and can result in poor condition and poor breeding.

Water may be available by access to natural watercourses, but care should be exercised when inspecting small watercourses that they are in fact permanent rather than temporary. More frequently, water is supplied by an extensive underground piped distribution system of water troughs with automatic floats to regulate the level and prevent overflow.

• Daily or twice-daily routine water checks for every situation are a critical part of stud farm management.

Sufficient water space must be provided for larger groups of horses. Moreover, it is essential that the water is clean and, in summer, that it is in such volume as to be cool, rather than hot from too small a volume. Automatic water troughs in stables are often too small and rarely allow a thirsty horse to have an uninterrupted drink before the water level becomes too low. A more satisfactory volume of 20–30 liters should be provided, usually in buckets.

Paddock water troughs should have a secure drainage plug to allow ease of cleaning. Regular cleaning is essential to prevent build-up of algae and decayed matter. Volume-controlling float valves should be protected from interference by the horses, either by guards or by being out of reach. Horses will play with accessible floats, often causing loss of water, muddy surrounds and, if undetected, severe loss from the main water supply. Long or round troughs provide the best cool water for horses and plenty of room for them to move around.

Continuous fresh water supplies are also essential if pastures are to be irrigated effectively; shortages of supply can be particularly harmful to a stud operation.

Topography

Rolling land has an advantage over flat land in that sites for barns, gates, roads, etc. can be sited away from storm water run-off areas, thus avoiding excessive mud in areas with high levels of traffic. It is important to observe the land after major rainfall. Moderately hilly or rolling terrain, such as the Epsom Downs in England, is often favored by growers of athletic breeds of horses on the basis that exercising on that type of land favors the development of bone, muscle and condition.

Soil or land type

The productivity of the soil is important for growing quality forage. Aspects such as depth of the topsoil, organic matter in the soil and drainage are significant.

Although a sandy loam soil is widely regarded as the ideal for growing grass and horses, it is, unfortunately, also ideal for many arable crops. Market pressures force the cost of this land higher than might be justified by the commercial return on horses.

Large amounts of rock or shale in the soil, which are not conducive to healthy feet, and very heavy clay soils that impede drainage are undesirable soil types and are often poor forage producers.

Trees and natural shelter

Shade from trees is beneficial in hot climates. However, in many circumstances, particularly if there are feed shortages (i.e. roughage), horses will destroy the trees by eating the bark (Fig. 1.2). Simple trunk protectors may be effective in preventing this. Furthermore, some trees are potentially poisonous. In the UK, many older properties have ancient trees that are very dangerous (e.g. yew, red oak, and laburnum).

FIG. 1.2 Boredom and lack of roughage often lead to horses causing severe damage to tree trunks, such as this ring-barked tree in the paddock.

Trees in areas prone to severe thunderstorms are potentially lethal lightning conductors. Fencing off the areas concerned is more difficult if there is to be any benefit from the trees in terms of shade or shelter provision. Lightning conductors are effective measures to reduce the risks.

Properties that have few effective shade or shelter trees are seldom used for stud farms unless there is the potential to grow them. Fast-growing eucalyptus, poplar or conifer trees can provide shelter within a few years. There are also esthetic aspects of stud farming that depend on trees.

A row of trees can be planted as a windbreak outside a fence line (Fig. 1.3) and horses will appreciate the protection they afford in the worst weather conditions.

FIG. 1.3 Line of shade trees planted between paddocks.

Shade houses/field shelters

These can be simple constructions of four posts with a shade cloth roof in dry climates (Fig. 1.4), or an iron-roofed, more solid waterproof construction of wooden panels or sheet and brick, in which the feeding and water facilities are placed. The protection afforded by shelters is also helpful where Musca flies and culicoides midges are a problem as these invade darkened shade areas less frequently than open-air paddocks with no cover.

FIG. 1.4 Simple sun shelter constructed of upright posts supporting a shade cloth roof.

Where prevailing winter winds are severe, shelters also provide protection from inclement weather. Old hay-storage sheds are often converted into low-cost shelters against, heat, cold and wet conditions (Fig. 1.5).

FIG. 1.5 Old hay-storage shed, providing shelter in both winter and summer.

ROADS AND ACCESS

Consideration should be given to access to the farm by the services that will be required. Delivery of construction materials, maintenance needs, service personnel and eventually transportation of animals and foodstuffs require decent hard-surfaced roads with reasonable access to the farm for suitable vehicles. In the UK, small country lanes can be a serious limitation for modern transporters, but by compensation they afford some sense of security. Careful planning of access roads, which should be kept wide enough for vehicles capable of moving horses (particularly mares, foals and young horses) is very important to allow ease of access to all points of the farm. Roads can be used to separate paddocks and so may act as effective quarantine barriers in case of disease outbreaks. They also allow planting of shade trees and installation of water conduits without having to interfere with the fields themselves. Free movement of feed vehicles and farm machinery, and the transfer of mares/foals to other locations on the farm without entry to other occupied paddocks, are also important advantages of a carefully planned road structure.

The movement of horses (possibly stallions or mares with foals at foot) by leading them should not be unduly risky; crossing main traffic routes or railway lines is fraught with danger and increases the risks to man and horse. Consideration should be given to possible escaped horses: gates and other restrictive measures such as walls and fences should ultimately allow the animals to be recaptured easily.

Connections to basic utilities such as water, electricity and gas need to be planned. Drainage and handling of waste must also be considered carefully if disease is to be limited.

Buildings

The basic requirements include adequate space for exercise, secure fencing, shelter according to the climatic conditions and special requirements of the operation, and a workable layout dedicated to safe and efficient execution of the intended functions.

Facilities are functionally the same for any size of operation, with the need for:

• Stallion boxes (and exercise yards).
• Mare boxes (for mares due for service, pregnant mares and mares with foals).
• Exercise yards and paddocks.
• ‘Hospital’ facilities comprising loose boxes for mares with sick foals.
• Facilities to hold and store feed (grains, chaff and hay) and bedding.

Farm layout

Before the specific layout of the operation is designed, careful regard to the functions required of the facility is essential. The plan must be carefully made before the first post hole is dug. Basic questions include:

• Will stallions be standing at the stud with their own ‘book’ of mares or will they simply be used for artificial insemination?
• If stallions are to be used, how many will be kept and what is their expected ‘book’?
• Will outside mares be brought in for breeding and, if so, how many and over what period?
• Will mares be visiting the stud to foal in order to get better supervision and foal care and to maximize the use of the foal heat?
• Will there be permanently resident mares on the farm and will these take precedence over visiting mares?
• Will weanling foals and yearlings be held on the premises? If so, will they be in contact with other outside horses or will they be kept segregated?
• Will a high level of veterinary attention be expected (will a veterinarian live on the farm?) or will this be more casual?
• Should there be isolation facilities for new animals? This is a very important aspect, and should be discussed in careful detail with the consulting veterinarian.
• How long will mares (with or without foals at foot) remain on the stud after covering?

These questions should yield a list of the facilities that are required immediately and for future developments. Ultimately, the safety of personnel and the well-being of the animals must be paramount in the design and construction of a stud farm. The nature of horses is such that their management is inherently dangerous and a full understanding of the potential hazards will limit the problems.

The basic requirements include:

• A stallion barn.
• Mare barn(s).
• Foaling facilities.
• Teasing facilities.
• Hay/feed storage.
• Office.
• Housing for staff.
• Veterinary examination area and laboratory facilities.
• Pastures and exercise paddocks for stallion(s), mares and foals, barren and pregnant mares, and yearlings/weanlings.

With the essential structures in mind, a plan should be developed for the relationship of each unit to pastures, paddocks, roads, water lines, utility connections, etc. so that the whole facility will be coordinated. Each unit should be able to function independently from the others.

• The breeding unit might contain mare and stallion housing, a breeding area, mare examination stocks/chute, laboratory, loading and unloading facilities, feed and hay storage and equipment sheds.
• An isolation facility for new arrivals should be located so that farm traffic will not cross-contaminate other portions of the farm (a separate drug-treatment area should be kept and made secure).
• A separate, self-contained unit is indicated for weaning and for longer-term housing of weanlings. Weaning is a stressful event for both mares and foals and injuries are commonplace even when facilities are ideal.

The underlying threat of infectious disease should not ever be overlooked. The potential catastrophe that can follow from the speed of spread and the economic damage from an outbreak of an infectious disease such as contagious equine metritis should not be forgotten. Serious economic danger from possible outbreaks of virus abortion and strangles creates the necessity for quarantine facilities (yards, stables, and paddocks) that are separate and distinct from the main farm area. Quarantine facilities should work on the principle of an ‘all-in all-out’ policy. Simply, this means that a group of horses held in quarantine for the required time must be kept separate from any new arrivals because of the possibility of cross-contamination in both directions if they are mixed. On large farms, this can mean very complex horse-holding facilities with enforceable management methods that prevent the breakdown of quarantine.

Visiting walk-in mares should be carefully segregated from home farm or live-in mares. Head collars, bridles, etc. must be thoroughly cleaned and/or sterilized if any suspected problems arise, and gear that is used in pre-entry (quarantine) areas should not be used elsewhere in order to minimize disease spread.

Strict control of stray dogs, cats and vermin such as foxes, rats and mice is necessary, especially if virus abortion erupts. Serious spread to adjoining paddocks can occur when dogs and carrion-eating birds spread infected aborted material.

FENCING

Safe fencing is essential on a stud farm. The horses on the facility, whether highly valuable Thoroughbred or other purebred horses or animals of lesser value, provide the raw material on which the stud functions. Their safe restraint is vital. All fences have some measure of danger: the more secure and solid the fence, the more solid fracture-type injuries occur; with star posts and wire, there are leg injuries from the wire and body injury from the pickets. When panicked by storms, etc., horses may break, or become entangled in, any type of fencing.

A survey of fence-related injuries³ supported the contention that no fence is horse-proof and free of potential hazard. The survey pointed out that the highest rate of serious injury occurred with barbed wire fencing, followed by high-tensile steel wire and page wire. Wooden fences (post and rail, and post and board) had high rates of injury, but those injuries were less severe than those related to wire. Although these results are not surprising, the fact that barbed wire fencing on metal posts is the most economical in terms of both materials and installation means that these fences will probably not disappear.

Selecting and building fencing for horses is an exercise in compromise. First, it must be recognized that there are no totally safe fences for horses. The animal’s basic nature is to run from real or perceived danger. If that flight is blocked by anything, a collision is a strong possibility. The options are to attempt to run through or jump over the fence. The results may vary from escape to serious injury from splintered fence boards or unyielding posts or wire. Moreover, the consequences of escape, whether in one piece or not, may produce further injury. Another cause for concern is the altercation between horses that can occur at the right-angled corners of a fence, in which the aggressors pin the recipient in the corner and settle the dispute. The dilemma, then, is whether to select a solid unbreakable fence or one that will fall apart on contact. In both cases there is ample opportunity for injury.

THE NEWBORN FOAL

Derek Knottenbelt

NEONATAL PHYSIOLOGY

The changes that the newborn foal must make at birth are very profound, involving to a lesser or greater degree almost all the body systems.

CARDIORESPIRATORY ADAPTATION

The transition from a fetus that is protected and nourished within the uterus to the free-living neonatal foal is probably the most profound change the foal will have to face. Airway clearance and the establishment of a normal respiratory function are vital. This is integrally coordinated with the cardiovascular adaptations that need to occur. Passage of the foal through the birth canal provides significant beneficial thoracic compression to drive excess fluid from the airway. Foals delivered by cesarean section do not have this mechanism and so need extra care for a clear airway to be established.

At the moment of birth the lungs must expand and the pulmonary circulation ‘switched-on’ to ensure a perfect ventilation–perfusion match between the two sides of the circulatory system. The change to pulmonary breathing and the circulatory adjustments that must accompany such a change within minutes of birth must be perfect if the foal is to survive and be able to move quickly to ensure safety.¹ Up to this point the blood from the pulmonary artery is shunted via the ductus arteriosus into the aortic circulation as a result of the high resistance afforded by the collapsed lungs and the relatively low aortic pressure. Oxygen-saturated blood arriving in the caudal vena cava from the placental vessels passes through the foramen ovale to the left atrium so that the brain receives freshly oxygenated blood. This pathway is obliterated within the first few weeks of life.²

At the moment of birth the lungs expand in response to a dramatic rise in PCO₂. This reduces the pressure in the pulmonary artery to below that in the aorta and so blood is directed into the lungs, with some being shunted by the relatively high aortic pressure into the pulmonary artery. At the same time there is no further need for the foramen ovale. The highly elastic nature of the ductus arteriosus means that some shunting one way or the other is present for up to 48–72 hours, but thereafter the ductus closes and becomes a fibrous band.

In the newborn foal respiration is often gasping in character and necessarily rapid as the foal attempts first to ensure full insufflation of the lungs and then to correct the acid–base imbalances that have arisen during the birth process. The efficiency of oxygenation of the blood is profoundly affected by the breathing pattern and any decrease in ventilation can alter the blood oxygen severely (and possibly dangerously).

The position the foal adopts also influences the oxygenation of blood. A foal in lateral recumbency may have a markedly lower partial pressure of arterial oxygen than one in sternal recumbency. This forms one of the most important principles of the management of neonatal foals. Also, the chest wall of the newborn foal is very compliant and so any respiratory disorder may have a disproportionate adverse influence on lung efficiency.³

Cardiac murmurs in foals

Although congenital defects of the heart and great vessels are rare, up to 90% of newborn foals have obvious continuous murmurs associated with a patent ductus arteriosus that are audible over the left base of the heart for the first 15–30 minutes of life.⁴ In most cases the murmurs will not be audible by 72 hours, but some may persist for some weeks.⁵ Murmurs are also commonly associated with sepsis, fever, anemia, etc.; these may vary from day to day.

Note:

• A ventricular septal defect presents a persistent, severe, systolic murmur associated with left–right shunt that increases with exercise. The murmur is usually more audible on the right side of the chest but may be inaudible or left-sided.

If cyanosis is present with a murmur it may indicate:

• Respiratory distress syndrome or pneumonia with functional murmur.
• A significant congenital heart lesion resulting in pulmonary overcirculation/edema.
• Complex heart defects with right–left shunting, causing systemic arterial desaturation.

Arrhythmia, including atrial fibrillation, atrial tachycardia and ventricular depolarization, is also common in newborn foals within the first 15–30 minutes of life. However, although such events could be alarming they are almost invariably due to high vagal tone and will resolve spontaneously over a short period.⁶ It may be unwise to perform an electrocardiographic examination on a very new foal because the results may be misleadingly alarming. Differentiation of the abnormal is the challenge for the clinician.

LOCOMOTION

The foal needs to rise quickly to its feet and to move with certainty. This means that the muscles and skeleton also need to adapt quickly to new forces and functions. This also involves the nervous system, which has to perform a vast range of functions that have been only ‘tested’ in utero. It would be a major disadvantage if a full-term foal were to practice and develop the full range of muscular activity in utero. There is some evidence that in utero movement of the foal becomes progressively more limited in the last months of pregnancy. Owners might therefore report that the foal’s movements have reduced or may even have apparently stopped altogether, suggesting that there may be a problem with the pregnancy. The limited movement in the later stages of pregnancy may predispose the relatively long-legged foal to abnormalities of growth and discrepancies between bony growth (over which there is almost no control) and tendon/ligament growth (which is probably coordinated by movement, posture and forces applied during their development).

ALIMENTATION

The next obvious major adaptation is the change from placental nutrition to alimentation. In order for the foal to feed effectively it must first have a perception/instinct to rise and then to seek the teat. Sight may be less important than would be expected but it obviously helps. Having once located the teat it must be in a position to suckle effectively and to swallow. Once swallowed, the milk must be delivered to the gastrointestinal tract and then digested efficiently. The gut must be fully patent to the anus and there should be no physical, neurological or other obstruction. The waste material from the digestive processes, which have also been going on during gestation (the meconium), have to be passed shortly after birth. The residues from digestion of colostrum support this by a laxative effect.

Milk is the source of nutrients for the neonatal mammal and the composition of the mammary secretion changes considerably with time.⁷ In the first hours after birth the milk is rich in immunoglobulins (colostrum). It is tempting to assume that milk provides all the nutritional requirements for the foal. However, in the longer term this is not necessarily so; foals need to supplement the milk feed with other ingesta within weeks of birth and will often be seen to take grass or hay within days of birth. Although natural mare’s milk is used to provide the formula for the preparation of artificial milk supplements, it does contain a delicately balanced variety of essential nutrients, including vitamins, minerals and enzymes, and artificial milk replacers are unlikely ever to match the gold standard of normal milk for any particular species.

The normal foal has a defined demand for food materials, but the abnormal or sick foal will inevitably have an increased demand for all the components. The demand for energy is often at least 50% above normal and can be much higher. The same applies to protein and fats as well as minerals and vitamins. Premature foals require extra food to complete organ maturation, but infection, fever, etc. place extreme demands on the foal’s ability to ingest enough raw materials. In reality, a sick foal often has a reduced appetite and so can easily fall into a downward spiral.

The specific requirements of the normal newborn foal are:

• Energy: 120–150 kcal/day.
• Protein: 5.5–6.0 g/kg/day.

Normal feeding should result in a normal growth rate (weight gain) of around 1.25–1.5 kg/day in a Thoroughbred foal.

• The normal birth weight of a Thoroughbred foal is 46–52 kg (42–48 kg for primiparae).

NEUROLOGICAL FUNCTION

The nervous system has an additional role in the adaptive period with the employment of the senses and mentation, including maternal imprinting/recognition and behavior. Survival will clearly depend on these as much as the ability to stand and breathe.

RENAL FUNCTION

Urinary excretion begins during gestation, with passage of urine into the bladder and then into the allantoic space. A smaller volume of urine will pass into the amniotic fluid via the urethra. The mean urine production in a neonatal foal is around 145–155 ml/kg bodyweight per day.⁸ This figure is far higher than in mature horses. These factors can be explained simply by the fact that the neonatal kidney is not functionally mature at birth and so renal concentration of urine is much less efficient than in adult horses. Foal urine is frequently more dilute than that of adult horses. The naturally high fluid intake and the lack of concentrating ability means that a foal’s urine has a naturally low specific gravity. The inability to concentrate urine means that it may remain relatively dilute in the face of dehydrating conditions that might otherwise be expected to cause urinary concentration. Foals also often have a relatively high urinary protein concentration⁹ and this can be significant, even in the normal foal. Furthermore the ability of the kidney to withstand toxic insult and to excrete some drugs etc. efficiently may be very immature. Therefore, drugs and chemicals that damage renal tissue might be expected to have an enhanced toxicity in foals.

The first passage of urine is an important event with respect to neonatal assessment (see p. 371). Colt foals usually pass their first urine at around 5–6 hours of age. By contrast, filly foals may delay their first micturition up to 10–11 hours. Observation of the first and subsequent micturition is an important stud procedure and the timing of the first natural urination has implications for those foals that have urinary tract defects such as patent bladder or ruptured ureters.

ENDOCRINE FUNCTION

The development of the endocrine system is very complex, but again maturation should coordinate with the change to outside life. Reliance upon the endogenous homeostatic mechanisms for almost all biochemical functions of the body is paramount. Unfortunately, we are uncertain of the specific changes that occur in the foal. Most statements related to endocrine adaptation are extrapolated from other species, particularly man. Although the relevance of these is probably minimal, in any mammal there will clearly be similarities that are justifiably assumed to operate.

THERMAL REGULATION

The neonatal foal is born wet and even in the best of circumstances will have to withstand a thermal shock at the time of birth. The ambient temperature is rarely high enough to overcome heat lost by evaporation or by direct loss into the cold undersurface. The considerable muscular effort that foals exert at the time of birth will compensate for some of this, but there is almost inevitably a fall in body temperature at birth.¹⁰ Body temperatures below 37°C are regarded as hypothermic and can precipitate a shock-like state. Significantly, hyperthermia can also have serious effects on the foal and temperatures above 40°C can cause convulsions and coma.

ASSESSMENT OF A FOAL’S RISK CATEGORY

The concept of a risk category for foals¹¹ has been used for many years and has been instrumental in saving many lives. A system involving three broad categories, in which the foal is classed as high-risk, moderate-risk or low-risk, is most widely used.¹² This is simple and serves the purpose well. A two-category classification is a simpler method that avoids the equivocal moderate category and has the advantage that more foals will be classified as high-risk and are therefore likely to be monitored more closely. The recognition that a problem might be present will enable the clinician to take pre-emptive measures to minimize any clinical consequences. On the basis that prevention is better than cure, the system has much to commend it. The concept should be used to guide the level of supervision and interference for a newborn foal. All management strategies for pregnant mares should be directed towards detection of potential or actual problems before they are so advanced that therapy may not be effective.

Why is risk categorization useful?

An assessment of the likely risk category of the foal will be of considerable benefit to its survival. A predesignated high-risk foaling provides a good chance of improving the survival rate by taking suitable planned measures in advance. Some factors can be predicted (particularly those relating to the mare and her breeding history) but others become significant as the pregnancy and parturition advance. In considering these factors the reproductive and general history of the mare and the pregnancy is paramount. Furthermore, it is important to regularly assess both mare and the unborn foal during gestation so that potential problems can be identified early.

It is virtually impossible to categorize mares without any historical information and in this case they should probably be classified as high-risk immediately. The major problem here is that those with no history are probably those that are of less importance to their owners and their classification may be less significant.

High-risk mares are therefore those in which possible complications can be expected. This means that parturition can be monitored closely and completely. In this way a higher foal survival rate can be expected. An additional benefit is that the survival rate of mares can also be improved and in most such cases their future fertility can be supported.

• Risk factors can be predicted from an accurate history of the mare and the pregnancy.
• Some of the factors that direct the classification of risk category of the foal will arise during the delivery or immediately afterwards. Therefore, while a foal could fit into the low-risk category until delivery it could be reclassified into a higher risk category as a result of events during or immediately after delivery. The clinician will need to be flexible in the classification and take appropriate steps to ensure that the foal has the best possible chance of survival.
• For example:
• If during a routine late-gestation check in a low-risk mare significant udder development is observed and there is ultrasonographic evidence of placental edema or separation, the pregnancy can immediately be classified as high-risk. Repeated examinations at sensible intervals may then allow this to be monitored up to and including delivery.
• A foal that is born to a low-risk mare could be exposed to traumatic events or infection at the time of birth; it should then immediately be reclassified as high-risk.

High-risk foals

These are cases in which there is a significant danger to the life of the foal as a result of:

• Maternal circumstances and conditions.
• Events occurring around and during parturition.
• Conditions and circumstances arising immediately after delivery of the foal.

Maternal conditions

Factors that are present at any stage before birth may have a profound effect on the prognosis for the pregnancy (see Table 11.1). In particular, any factors that influence placental nourishment of the foal or subsequent colostrum production are of major importance.

 

Possible consequences of maternal conditions on the foal

• Prolonged or shortened pregnancy.
• Discrepancy between size of foal and size of mare and her birth canal.
• History of problem foals (e.g. dysmature/premature, neonatal isoerythrolysis, neonatal maladjustment/asphyxia syndrome, congenital defects).
• History of previous uterine torsion in present or previous pregnancy.
• History of colostral leakage or premature lactation prior to delivery.
• Purulent vaginal discharge or vaginal bleeding.
• Disease/injury with or without drug administration.
• Pelvic injuries (fresh or long-standing), or space-occupying lesions that might alter the dimensions and congruity of the birth canal.
• Lameness or neurological disorders that prevent normal behavior and posture prior to and during delivery.
• Pyrexia/toxemia/septicemia/endotoxemia.
• Poor bodily condition/poor nutritional status (primary or secondary).
• Hydrops amni (very rare).
• Colic/colic surgery/other surgery (cesarean section or uterine torsion)/anesthesia.
• Primiparous delivery (especially if suspect behavior) or history of aggression.
• Twin pregnancy.
• Transport prior to delivery (last 4 weeks of gestation).

Parturition conditions

Factors affecting the process of parturition would necessarily have a profound effect on the viability of the foal (see Table 11.2). Any factor that affects the ability of the foal to adapt (e.g. loss of blood from early cord separation may cause a slow adaptive period and inability to rise) will have significance:

Table 11.2

Possible consequences of parturition conditions on the foal

• Prematurity (gestational age <320 days) (see p. 372).
• Prolonged gestation (overdue foal).
• Prolonged labor/dystocia.
• Perineal laceration/rectovaginal fistulae.
• ‘Red bag’ delivery (early placental separation).
• Premature rupture of fetal membranes.
• Induced parturition.
• Colostral leakage/early lactation.
• Early (premature) cord separation.
• Uterine bruising/tearing.
• Vaginal blood loss from mare.
• Cesarean section.

Factors involving the foal itself or becoming apparent in the foal at delivery

• Obvious congenital abnormalities (in any organ system).
• Weakness or ‘small for breed’ foals.
• Meconium staining of foal or fetal membranes.
• Trauma/predation.
• Potential infection (poor hygiene or management).
• Low or no colostral intake (either because of disability or lack of natural behavior).
• Twin foals.
• Death of dam.

Low-risk foals

A foal can be classified as low risk if:

• There are no maternal factors that might adversely affect survival of the foal.
• Gestation is of normal duration and there have been no complications with the health of the mare during pregnancy (or any previous pregnancy).

Note:

• Mean gestation length is 340 days (range 330–350 days). However, normal gestation can be well in excess of 350 days and there are many reports of pregnancies of over 365 days resulting in a normal foal).
• Delivery of the foal is normal and without complication or delays.

Note:

• Parturition should in this classification take no more than 20–30 minutes from start to finish.
• No manipulation or interference is required either to the foal or to the mare.
• The adaptive period should be normal with the foal standing within 2 hours and suckling by 3 hours.
• Colostral intake is effective and raises the foal’s IgG concentration to over 8–10 g/l.
• The placenta is normal and is passed freely.
• There are no external dangers (such as infections in other horses, inclement weather, predators, etc.).

Moderate-risk foals

A foal is classified as moderate-risk if only one of the factors that increase its risk is present. Such factors could involve either the mare or the foal itself. In this respect, it is important to remember that the placenta is derived entirely from the foal; there is no component of the placental membranes that belongs to the mare.

Note:

• In practical situations a classification of high-risk or low-risk is an effective compromise because a moderate risk may serve only to over-emphasize minor problems or under-emphasize the more major ones.

EVENTS FOLLOWING DELIVERY IN THE NORMAL FOAL (THE ADAPTIVE PERIOD)

The adaptive period is the time during which the foal must adjust from the uterine environment to the ‘independent dependence’ of extrauterine life.

It is important to recognize the normal events that take place (see Table 11.3) so that any abnormal events can be quickly recognized and appropriate corrective action taken. Unfortunately, there are wide variations in the normal pattern of delivery and neonatal adaptation, thus making the decision to interfere difficult. The extent of veterinary intervention will often depend heavily on the experience of the owner/handler or groom. More experienced grooms may not need anything like as much support and will also often recognize problems earlier than less experienced grooms. Furthermore, the value of the foal and any complications during pregnancy will often dictate the role of the veterinary surgeon. Probably the majority of foalings attended by veterinarians are recognizably abnormal in some respect.

 

Events occurring in foals during the first 72 hours of life

The recognition of abnormalities can be more difficult than would appear. Intervention needs to be limited but sensible. There is little point in leaving an obviously abnormal situation to sort itself out; conversely, interfering when there is no need to do so can do harm.

• The foal is delivered during second-stage labor. Usually the foal is within the amnion, which usually breaks spontaneously as a result of opposing movements of the forelimbs and head.
• The foal takes its first breaths with chest and abdominal movements (usually within 30 seconds of delivery of the chest). There may be a series of initial gasps with neck arching.

This is not a signal for intervention unless the cord has separated.

• The normal respiratory pattern is rapidly established. The newborn foal will show fast and deep breathing; this is accompanied by a dramatic rise in arterial blood oxygen (PaO₂) which progressively increases with increasing muscular effort. There are significant other signs for a similar increase in respiration rate (see below).
• The mare will usually undergo a period of tranquility (lasting up to 40 minutes), during which time the foal shakes its head and gains sternal recumbency with ‘righting reflex’. Throughout this the mare remains quiet (usually in sternal recumbency) and will often vocalize to the foal.

This is not a sign for intervention.

• The foal may show strong blinking reflexes as hearing and vision are established. It may whinny on its own or in response to the mare. The foal’s head bobs up and down markedly, and suckling responses with lips and mouth are present with increasing strength.
• The foal struggles and moves to the side of the mare. Usually the cord ruptures at this time, either because the foal moves or because the mare stands up. The cord usually ruptures about 6–8 minutes after delivery at a predetermined site (3–5 cm from the umbilicus). Shorter ruptures may have serious consequences, including internal hemorrhage. Severe tension on the cord at the umbilicus may also cause serious internal bleeding (although this is very rare). Premature rupture of the cord may compromise the foal (up to 25–30% of the foal blood volume can be lost).
• The mare nuzzles, licks and encourages the foal. In response, the foal makes its first attempts to stand, usually within 30 minutes of delivery.
• Normal foals will stand by around 45–90 minutes after delivery (often with apparent incoordination); they may fall several times before establishing a steady stance and the ability to move. A normal foal may take up to 2 hours before standing, but the longer it takes the greater the likelihood of a problem being present.
• The foal then seeks the mare’s udder (Fig. 11.1). This is often aimless at first but increases in accuracy. Once the teat is located a strong suckling reflex is established. The first effective suckling takes place within 60–90 minutes of delivery. In response, the mare will ‘let down her milk’ and the colostrum will be seen to stream from the teats.

FIG. 11.1 Foal seeking the teat.

• After about 30–60 minutes (especially if a feed has been successfully obtained) the foal will lie down again. The foal may make its first energetic steps on rising again, may jump up and down, and may then fall again. All foals have an inherent incoordination and may seem to be ataxic for the first 24 hours.

Note:

• The amnion must be distinguished from the chorioallantois and bladder.
• The correct time of interference needs to be recognized; minimal interference is desirable.
• Cutting the amnion is sometimes a desirable safety precaution; the foal’s nose can be uncovered and there is then less risk of asphyxia. However, it is important not to disturb the mare if at all possible while this is done.
• Cord rupture usually causes slight blood flow, most often from the placental end (venous flow at low pressure). Severe arterial blood loss from the umbilical end of a ruptured cord requires immediate attention: clamp with sterile artery forceps or umbilical clamp (plastic bag clamps are useful). The cord should not be tied with string, etc.
• Dress the navel (e.g. with teat dip or povidone iodine solution, chlorhexidine or antibiotic spray) within 30 minutes of delivery. Recent work suggests that the best results are obtained with chlorhexidine and that povidone iodine may not be as effective as was first thought.¹³Ensure thorough soaking of the navel but avoid over-handling. Aerosol sprays may give a false impression of their effectiveness because they are under mild pressure and their cover is more defined and can be seen, but the antibacterial effects are probably poor and nonpersistent. The antibiotic may not be effective against the organisms present (many significant Gram-negative bacteria, including Escherichia coli, are tetracycline-resistant).
• Full hygiene measures are imperative for anyone handling the foal. It is remarkable how few stud personnel have any concept of cleanliness when handling foals and parturient mares.
• It is advisable to wear gloves and overalls that can be changed frequently on every occasion when dealing with neonatal foals (preferably protective clothing should be changed between different foals). Washing hands and changing overalls frequently also minimizes cross-contamination between mares foaling at the same time.
• All reasonable hygiene precautions should be in effect at all times, including the provision of freshly washed or disposable aprons/gowns for each mare/foal and for each stud. It is best to advise the stud to maintain a stock of these for their own personnel and for visiting veterinarians.

EVALUATION OF THE NEWBORN FOAL

Evaluation of the newborn foal is very important as it provides the first and earliest opportunity to assess its potential viability. It also allows a veterinarian to assess whether there is anything that needs to be addressed immediately, such as provision of oxygen, artificial (positive-pressure) ventilation, blood transfusion, antibiotics, etc.

Foals are best scored at 1–3 minutes of age. Note, however, that foaling mares exhibit a natural period of tranquility following the expulsion of the foal (the foal usually still has its hind legs in the birth canal). During this stage the foal’s umbilical circulation is still very active (a pulse is still palpable in the umbilical artery) and the uterus is actively contracting. This causes a progressive arterial resistance and an active return of the foal’s venous blood into its systemic circulation. This is a very important stage of delivery and disturbances to assess the foal at this stage may be counterproductive. Early rupture of the cord resulting from early disturbance of the mare may result in significant deprivation for the foal. Up to 1 liter of circulating blood may be left in the placental circulation when rupture is rapid. Adaptation must under these circumstances be abrupt and this allows little scope for interference in the event of a problem.

The APGAR scoring system

The APGAR system is a scoring system that is used to assess Appearance, Pulse (rate), Grimace (response), Activity (muscle tone), and Respiration (rate). It is a simple method that can be used for the immediate assessment of the foal during the first 3 minutes of birth (see Table 11.4). A more complex system in which muscular activity parameters carry a higher loading can be used in specialist hospitals for older foals (up to 2 hours) (see Table 11.5).

 

APGAR scoring method for the assessment of a foal within 3 minutes of birth

Score: normal, 7–8; moderately depressed, 4–6; markedly depressed, 1–4; 0, dead.

 

Advanced APGAR score sheet for foals (at 10 minutes of age)

Interpretation and actions: 11–14, normal (continue to monitor; avoid interference); 7–10, moderate depression (administer nasal oxygen; stimulation by external rubbing; encourage sternal recumbency); 2–6, severe depression (administer doxapram, nasal oxygen; external stimulation; encourage sternal recumbency); 0–2, dead or almost dead (administer artificial respiration and full cardiopulmonary resuscitation for limited time only; do not waste time on these foals).

• Provided problems are recognized early, even some seriously depressed foals can be saved with effective intensive care. Some conditions arise before birth, so accurate history and careful clinical assessment is vital. Owners can be taught to assess the foal at birth; this does not reduce the necessity for a full examination as soon after birth as possible.
• Many high-risk foals look relatively normal at birth and up to 12–18 hours of age. Once problems develop, deterioration is usually rapid. This makes early recognition of problems an important management procedure.
• Newborn foals that are high-risk or that show any evidence of respiratory or neurological (or other) compromise, should be subjected to APGAR scoring at regular intervals over the first 30 minutes. Apparently normal foals should be scored only once and then left alone.

ROUTINE VETERINARY AND MANAGEMENT PROCEDURES FOR A NEWBORN FOAL

In performing the following procedures, the groom/veterinarian must balance the need to interfere against the possible disturbance that this creates. If a foal is delivered in a safe clean environment, little interference should be required and routine procedures can be delayed until the foal is standing and has bonded with the mare.

1. Establish a clear airway

• Gravity can be used to help; slope the foal down from the tail end. Lifting the foal by the back legs can be used, but is difficult and very disturbing to the mare.
• If necessary use aspiration (short sharp aspirations are better than prolonged suction). Suitable suction/aspiration systems are available in disposable form.
• Ventilation can be encouraged by gently blowing into the nose or by using a mask system fitted to a pressure-limited pump.

2. Umbilical care

• Ideally the navel should be immersed in a 0.5% solution of chlorhexidine (this should be repeated every 6 hours for the first 24 hours).
• The use of povidone iodine for this purpose has been called into question.¹⁵Strong solutions of iodine or tincture of iodine can cause burning and necrosis of the umbilical stump.
• Aerosolized antibiotic sprays (e.g. tetracycline) are useful in that they dry the moist stump while applying a dose of antibiotic but have very limited efficacy and short duration.

3. Administration of colostrum by nasogastric tube

• At birth, oral nutrient intake becomes the sole source of nutrition and the importance of colostral antibody transfer cannot be overstated.

Note:

• It is routine practice on many stud farms to administer 250–300 ml of good-quality colostrum to newborn foals. The merits of this are viewed as greater than the unwanted consequences of disturbance or stress.
• Many practitioners and stud owners believe that this measure is essential for the health of the newborn foal. Not only does it ensure good colostrum intake but it is also suggested to be an important measure for encouraging passage of meconium.
• Foals receiving immediate colostrum probably have a higher overall survival rate than those that are left to their own devices.
• Newborn foals can easily be intubated. A soft rubber tube (diameter <1 cm) is best and can be passed up the ventral meatus of the nose. Passage up the middle meatus is more difficult and tends to induce significant ethmoidal damage and bleeding.
• Always use as small a tube as possible that is consistent with requirements. Enteral feeding tubes are very much smaller and well tolerated, even allowing normal feeding to take place with the tube in situ.
• Usually the act of swallowing can be felt and the tube advanced gently but swiftly.

Note:

• Do not introduce any material down the tube until it is certain that the tube is in the esophagus.
• If you can blow and suck on the end of the tube, it is likely that it is in the trachea.
• If you cannot blow or suck, it is likely that the tube is kinked over itself and must be carefully withdrawn. Severe trauma can occur when this happens.
• If you can blow but cannot suck, the tube is most likely in the esophagus.
• The passage of the tube down the esophagus can usually be seen in the left jugular furrow.
• The tube can usually easily be palpated in the neck.
• There is usually some resistance to the passage of the tube in the esophagus.
• There is no resistance to the tube in the trachea and it may be ‘rattled’ within it.
• If the foal coughs it is likely that the tube is in the trachea.
• Aspiration of stomach contents means that the tube is correctly placed.

Long-term enteral nasogastric tubes can be introduced through a wider tube, which can then be removed. Enteral feeding tubes are commercially available (Nutrifoal Tubes^®). These tubes have a bag attachment for feeding up to 3 liters of liquid feed. It is essential to measure the length required before insertion; there have been occasions when extra length inserted into the stomach has caused the tube to tie itself into a knot, making removal impossible. The end of the tube should preferably be in the distal esophagus. Suture the end of the tube into the nostril or glue are tape to head collar (foal slip) to prevent rub removal. When using a long-term tube there is no need for the tube to reach the stomach; there is a slight risk of knotting if too much length is introduced. Wide tubes make for easier insertion but have a higher incidence of pharyngeal damage (including necrosis, abscessation, and inflammation); thin tubes are more inclined to blockage and can be rejected from the esophagus.

Once the tube is in position it should be briefly flushed with warm water and the end plugged. Aspiration of air can be a serious complication of long-term stomach tubes if the tube is left open.

Larger tubes can be left in situ for 24–36 hours (not longer), but enteral feeding tubes are well-tolerated for up to 4 days. Indicators for removal and replacement of the tube include:

• Pain.
• Coughing.
• Dysphagia and/or repeated swallowing.
• Nasal bleeding.

It is important to remember that a foal needs very small feeds repeated at regular intervals to try to mimic the natural state of feeding.

Nasal oxygen tubes are well tolerated by sick foals but less so as the foal gets better. The tube should be inserted so that the tip lies just within the internal nares. If the tube is advanced further it may induce repeated swallowing and less induces repeated sneezing/rejection.

4. Vaccination

Many studs routinely administer 3000–6000 IU tetanus antitoxin at, or soon after, birth regardless of the vaccination status of the mare. Tetanus vaccination (toxoid) can, in theory, be administered at birth but it is common practice to delay this for 2–3 weeks even in foals delivered to unvaccinated mares.

5. Antibiotics

A routine injection of a long-acting formulation of benzathine/procaine penicillin is commonly administered at birth or shortly afterwards. A full 3–5-day course of antibiotics is essential and best practice. Although the choice of penicillin would not seem to be the most appropriate as a prophylactic measure for neonatal septicemia (most such infections are Gram-negative against which simple penicillin has little or no effect), the occasional staphylococcal or streptococcal infection may be prevented by this.

6. Laboratory

The foal should be blood sampled (see below) at 12–16 hours for estimation of colostral transfer (IgG) and for routine hematology and biochemistry (see Table 11.6). At this stage the earliest evidence for impending problems can often be detected. If there is any suspicion of a problem, blood culture should be set up immediately. Cultures routinely take over 24 hours to yield any useful results. Although this can be a valuable prophylactic measure, it is an expensive procedure.

Table 11.6

Changes in a foal’s hematology and biochemistry parameters over the first 7 days of life

^aChanges more quickly if cord ruptures early.

^bSamples taken in lateral recumbency may be significantly higher: ±50 mmol/l.

^cSamples taken in lateral recumbency may be significantly lower: ±75 mmol/l.

Blood sampling

Venous sampling

Foals are very liable to venous/jugular thrombosis and thrombophlebitis and every care needs to be taken to ensure that:

• The minimum number of venepunctures consistent with requirements are performed.
• Full aseptic precautions are taken, especially if blood cultures are to be performed.
• As small a needle as possible is used.

Note:

• Very fine needles may result in damage to cells, etc.
• Usually a 20/21-gauge needle is adequate.
• 16/18-gauge needles are unnecessary and traumatize the vein significantly.

Suitable venepuncture sites, which can also be used for catheter placement, include:

• Jugular veins (do not damage both).
• Cephalic veins.
• Lateral thoracic veins.

The umbilical vein(s) can be used in foals less than 24 hours of age but this carries a significant risk of navel infection/septicemia.

The placental vessels provide a good source of blood without the need to interfere with the foal at all immediately after delivery (within 2 minutes). The samples will need to be taken from the ruptured placental vessels immediately the foal is delivered so that the breaking of the cord can be directly observed. Sampling from the intact umbilical vessels before cord separation is simple but may disturb the mare. Placid, experienced mares may allow this to be performed without making any attempt to rise.

Note:

• Vacuum tubes are not generally regarded as good for collection of horse blood. The erythrocyte fragility is such that significant variations, damage and errors can be induced by their use.
• It is better to use a syringe and needle, and after removing the needle introduce the blood into the opened tube.

Samples for blood culture should be placed immediately in biphasic blood culture medium in full aseptic manner. Other samples collected in conventional blood collection vials are of no value for blood culture. Swabs are even worse and should not be taken for culture purposes.

Note:

• It is important to consider the exact type of samples that might be required before they are obtained.
• Calculate the volume required for the containers to be used.
• It is not correct to put 1–2 ml into a 10-ml tube containing EDTA or other anticoagulant; smaller containers should be used when only limited volumes of blood are required. Most laboratories now need only a few milliliters of blood, serum or plasma to perform extensive ranges of hematology and biochemistry. A specific test may require specific anticoagulants, so it is worth checking what the best sample is.

For example:

A platelet count can only be reliably estimated from a citrated sample, whereas blood glucose should be performed on a fluoride–oxalate sample.

Arterial sampling

Arterial blood can be obtained from:

• The tarsal artery (best).
• The transverse facial artery behind the eye.
• Femoral or carotid arteries.

Alternative sites include the median artery, the facial artery and the umbilical artery (in foals less than 24 hours old). The umbilical artery can easily be located by close examination of the navel. It is sometimes necessary to cut across the very end of the severed cord to reveal the three major structures. The artery is obvious and can be cannulated easily; a long catheter needs to be used (at least 30 cm). The risk of infection is very high.

• Full aseptic precautions must be taken and pressure applied to the site of puncture for at least 10 minutes after sampling is completed.
• Use specially prepared syringes (with heparin) and needles (Pulsator^®, 3 ml with 0.7 mm × 25 gauge needle, single use arterial blood sampling system; Concord Laboratories, UK).
• Entry into the artery is indicated by the syringe self-filling.

CLINICAL EXAMINATION OF THE NEWBORN FOAL

It is impossible to perform a clinical examination of the foal without reference to the history relating to the dam, the pregnancy, and the foaling. The use of a proforma makes the examination simpler and the recording of the findings is important for subsequent examinations. Such a form helps ensure complete examination without serious omissions or errors. Events can change rapidly in foals and so repeated examinations are important to detect trends in physiological and pathological processes.

• The equine neonate can be difficult to examine effectively particularly when compromised or when very energetic.
• Some foals that are severely compromised by respiratory deficiencies can show considerable resistance to being handled and any attempt to forcibly restrain the foal may be counterproductive or dangerous.
• A detailed clinical examination should be performed on every foal; it is very easy to miss early signs of diseases that can progress rapidly beyond the point of recovery.

Disease is easily spread from stud to stud by fomites (fomites are substances, such as clothing, that are capable of absorbing and transmitting the contagium of disease) and contamination, so appropriate care needs to be exercised and demonstrated to lay persons. This has a beneficial effect upon the disease status of the studs in general and emphasizes the need for hygiene to the owners themselves.

PROTOCOL FOR EXAMINATION OF THE NEWBORN OR NEONATAL FOAL

The objective of a clinical examination (including the history) (see Fig. 11.2) is to establish:

FIG. 11.2 Examination of the newborn or neonatal foal.

• A diagnosis.
• A prognosis.
• A logical treatment plan to maximize the chances of a full recovery.

Symptomatic treatments for unknown conditions that have no identifiable diagnosis are commonplace and almost inevitable in practice. However, if a full history is obtained and a thorough clinical assessment performed it should be possible to establish at least a list of the problems that are present. From this list a presumptive diagnosis may be possible, although further diagnostic tests may be needed to eliminate some of the differential diagnoses. The main problem with many foal diseases is that delays in waiting for the results of tests may be harmful and could in some cases be too long to save the foal. Therefore, there are few opportunities for short cuts or presumptive tests. In every case, regardless of the possible diagnosis, the IgG concentration in the foal’s blood must be established.

History

The history of the stud farm, the mare and the foal are very important features of the investigation of disease. It is very easy to be drawn into the problems of the foal, but there may be helpful factors from a carefully derived history, including:

• Previous disease history of the property.
• Disease history of in-contact animals.
• Previous reproductive history of dam.
• Gestational age.
• Duration of parturition duration.
• Time taken to rise and to nurse.

Examination of the environment

The environment of the foal is important and the clinician needs to be aware of the implications of dirty versus clean stables, contact with other foals and/or adult horses and/or other species of animal.

• Foals born at the end of the stud season can be subjected to significantly increased challenge by infectious organisms than early foals. By contrast, the weather conditions and feeding of the mares can be more problematic in the early season.
• Many mares foaling in the early parts of the year are required to foal inside; this may add potential challenges to the foal and to the mare.

Examination of behavior

The behavior of the foal vis à vis the dam and its environment should be assessed early and certainly before any disturbances to either the dam or the foal.

Note:

• Maternal affinity and the presence or absence of any overtly abnormal behavior (e.g. convulsions, ataxia, colic or lethargy).
• The suckle enthusiasm and ability should be observed.
• Does the foal recognize the dam and is teat-seeking direct and effective?
• Does the foal appear to see normally? (Does it bump into walls, etc.?)

Note:

• Newborn foals are normally clumsy and may sometimes appear to be severely ataxic. It is often difficult to separate the normal state from pathological ones.
• Is feeding normal?
• Is there milk on the foal’s face (indicating that the foal has at least been in the right vicinity)?
• Is the mare’s udder full or empty, and is there evidence of milk loss over the lower hindlimbs?
• Is there evidence of nasal reflux of milk during or after feeding?
• The respiratory rate should be measured before handling the foal if at all possible.
• Is there any evidence of abnormal breathing pattern, rate or is there a nasal discharge?
• Observe and assess restraint (e.g. ‘flop’ reflex) (see Fig. 11.3).

FIG. 11.3 Normal and hypotonic foals.

Examination of vital signs

The vital signs should be recorded early, as they are likely to alter significantly with handling.

• Respiratory rate and character can be measured and should be assessed before restraint. After the foal has been restrained the chest should be auscultated carefully with a stethoscope.
• Heart and pulse rate/quality should be measured (it is wise to check multiple arteries if possible). An abnormally low heart rate is usually a serious indicator of compromise; a very high rate can indicate anemia, pain, infection, or toxemia.
• Mucous membrane color and capillary refill time should be measured and recorded. Normal mucous membranes are a uniform salmon-pink color, and the capillary refill time is normally less than 2 seconds. Again it is wise to use all the mucous membranes available as some may be misleading (e.g. a bruised eye). Furthermore, the mucous membrane color may not be a good indicator of the oxygenation status of blood. The mucous membranes may be pale as a result of loss of blood, or icteric if internal hemorrhage, red cell destruction or liver disease is present. The presence of petechial hemorrhage is usually significant and can indicate toxemia or serious septicemic infection.
• The rectal temperature is an important parameter for the foal. Subnormal temperatures can be serious but can be the result of errors of technique. Ideally, a digital thermometer should be used and it should be pressed gently against the rectal mucosa. Any abnormal temperatures should be repeated to test the accuracy. The extremities (feet/limbs and ears, nose, tail) should be palpated to detect altered temperature.
• Bodyweight should be obtained routinely, but this is unfortunately not commonly done. The weight of a foal can usually be obtained simply by deduction from the total of a handler and the foal on normal bathroom scales.
• The body condition score may be very difficult to assess in a newborn foal as the usual parameters are not easy to identify. However, it should be possible to establish if the foal is reasonably covered with muscle and the extent of fat can sometimes be assessed.

A logical anatomical or systems approach is essential for the clinical examination, and the examination should always be performed in the same way. This will ensure that nothing is missed out. With experience some short-cuts can be taken but even then this may be unwise. There is much to commend the ‘body systems’ type of examination technique because, although it is more time-consuming, it does ensure that every system is examined carefully and, in the process, allows every anatomical site to be examined more than once.

Note:

A proforma for clinical examination is a very useful aid to both the examination and the subsequent clinical assessment. Recording the results of the clinical examination in an understandable form is important so that:

• Progress (or otherwise) can be assessed.
• A colleague or referral center can make a true assessment of progression of signs.

DETAILED EXAMINATION OF THE BODY SYSTEMS

Cardiovascular system

• The heart rate should be 40–80 immediately after delivery, with rises up to 130–150 while attempting to stand. Over the first 7 days the rate should gradually fall to 60–70. Foals are easily excited or stressed, so handling may cause increases in the heart rate.
• Sinus arrhythmia may be present in the first few hours but should then stabilize.

Murmurs are common. The ductus arteriosus frequently remains patent for up to 48–72 hours; a characteristic ‘machinery murmur’ (often grade 3–4/5) may be heard predominantly at the level of the base of the heart (i.e. around the mid-point of the chest at the level of ribs 4–5). [The machinery murmur is a continuous, often vibratory, sound that increases and decreases with the changes in arterial blood pressure but which does not disappear at any stage in the cardiac cycle.]

• Serious heart defects may or may not have accompanying murmurs, and the associated signs may be subtle or dramatic.
• The normal pulse in a peripheral artery is usually only just palpable. Usually the facial, metatarsal and median arteries can be felt with the fingertips. It may be possible to feel the carotid pulse fairly easily deep in the lower quarter of the jugular groove.
• Normal blood pressure (measured from a tail cuff applied with the foal in lateral recumbency) is 35–45/85–90.
• The distal extremities such as the ears and feet should be warm.
• A jugular pulse is not normal. The distensibility of the jugular vein should be assessed; it should fill briskly unless the foal is hypovolemic.
• There are few palpable lymph nodes in the normal foal. Enlarged glands may be significant directly or they may be more noticeable if the foal is in poor bodily condition.
• As blood is also a part of the cardiovascular system, the color of the mucous membrane and the specific characteristics of a blood sample can be important aspects of the examination.

Respiratory system

Note:

• Because auscultation of the chest and upper airways alone is not a reliable means of assessing the respiratory function of newborn foals, all the associated features (including mucous membrane color, respiratory behavior and airflow) should be examined carefully.
• The resting respiratory rate and regularity of rhythm are best observed from a distance, without restraint or excitement. Thoracic/respiratory function should be very carefully assessed to ensure that nothing is missed.
• Immediately after birth the respiratory rate is normally >60 breaths/minute, but this falls after 1–2 hours to 20–40 breaths/minute.
• Breathing should require minimal effort, and should be smooth with passive elastic recoil during expiration. There should be equal airflow from both nostrils.
• Rapid respiration can be the result of many systemic conditions, including:

Blood loss.

Sepsis.

Fever.

Pain.

Shock.

• Significant respiratory difficulty can also arise from congenital deformity of the airway (choanal atresia, subepiglottic cyst formation, laryngeal deformity or functional disability, tracheal collapse).
• During rest and sleep, respiration can become irregular and there may be some snoring/stertor.
• Beware of paradoxical chest patterns (the chest moves in and the abdomen moves out during inspiration). Excessive chest or abdominal movement is best regarded as abnormal and should be investigated. The patency of the airway MUST be assessed in any foal showing respiratory difficulty.
• Auscultation of the chest is much easier in the foal than in the adult horse, but even in severe pathology (e.g. Rhodococcus equiabscessation) there may be few abnormal sounds. The dependent lung of a recumbent foal may be almost silent.
• Percussion of the chest is very useful and under-utilized.
• Absence of sounds is possibly more sinister than obvious adventitious noises.
• Foals seldom cough or have nasal discharges even in severe disease.
• Too few foals are subjected to blood gas studies, ultrasonography, endoscopy and radiography.

Arterial blood gas estimations provide the best index of respiratory efficiency in foals (see p. 364 for blood sampling technique).

Source-https://veteriankey.com/routine-stud-management-procedures