MANAGING GOOD BREEDING PRACTICES IN  SOW FOR OPTIMUM  PRODUCTIVITY

MANAGING GOOD BREEDING PRACTICES IN  SOW FOR OPTIMUM  PRODUCTIVITY

DR G. BHARGAV, NAINITAL, VO

Breeding or mating systems are the approach taken to pairing a boar and a gilt or sow for breeding in order to incorporate or maintain desired traits. Because the genetics of a pig plays an important role in its performance and meat quality, all pig producers should be familiar with breeding systems for pigs. This factsheet provides an introduction to pig breeding systems and heterosis. Practical swine breeding systems for small and beginning pig farmers are also discussed.

A sow is a female pig that has already had a litter and a gilt is a female pig that has not had a litter. Therefore, a gilt can be a pregnant animal (up until its first litter). Pigs are prolific and a sow can have many litters over the course of her lifetime.

As a rule of thumb in commercial industries, sows are often culled after their seventh litter because statistics show that sow productivity drops at that time to a point where higher production is attainable by replacing her with a gilt. Certainly some sows can be productive beyond the seventh litter and some gilts may not be as productive, but in large operations with many sows this culling ideal proves to make economic sense. When a sow is culled from the herd the young female that will take her place is often referred to as a replacement gilt.

Pig Mating Systems

A breed is defined as a group of animals sharing a common ancestry that have distinguishable, fixed characteristics who when mated with a member of the same breed will produce offspring with the same characteristics (Damron, 2013). Breeding or mating systems are the approach taken to pairing individuals for breeding in order to incorporate or maintain desired traits. There are two main type of mating strategies— positive assortive mating and negative assortive mating.  In positive assortive mating we breed like to like in order to narrow the genetic pool so that the desired traits express themselves more frequently.  In negative assortive mating we breed unlike to unlike in order to correct a deficiency or improve expression of a specific trait. Through these mating strategies five basic breeding systems arise (NSIF 2003):

• Inbreeding—breeding individuals who are very closely related within the breed.
• Linebreeding—a form of inbreeding which attempts to concentrate the inheritance of one ancestor or line of ancestors within a herd.
• Outcrossing—breeding individuals that are less closely related within the breed.
• Random mating within a breed—mating individuals within a breed without considering their pedigree.
• Crossbreeding—a planned approach to mating pigs of very different genetic backgrounds which typically results in heterosis. Heterosis is the improved performance of offspring compared to the average of their parents (NSIF, 2003).
• There are a number of breeding systems that can be adopted depending on the, requirements under the prevailing situations. However, the following procedures should be adopted for breed improvement.
• Selection and out-crossing: This can be adopted in all pig-breeding farms and by  farmers who produce breeding stock. This is a common method of breeding and multiplying purebred swine. The best procedure is intensive selection and out-crossing (mating of unrelated individuals of the same breed). Generally the results are quite good as some vigour will be obtained in the offspring with some gain in litter size, livability and growth rate. Out crossing is also done frequently to introduce a trait, which is lacking in a herd.
• Grading Up: The non-descript indigenous pig forms the bulk of the pig population in the country. It would be advantageous to grade up this population by the successive use of boars of either Yorkshire or Landrace breed, depending on the suitability of the breed to be used in the area. This would bring about an improvement in the productive traits of indigenous  pigs in graded stages. This method is also suited to many areas when management and feeding conditions do not justify the introduction of high-quality purebred stock.
• Cross breeding: In a number of areas, particularly in the neighbourhood of bacon factories, pig production with purebred stock of Yorkshire or Landrace breed has been introduced. It would be advantageous in these areas to introduce crossbreeding, e.g. crossing Yorkshire sows with a Landrace boar and vice versa. While there are several systems of crossbreeding, under the prevailing conditions either single crossing or criss-crossing would be suitable and can be practiced in intensive areas.
• Single crossing is the mating of a boar and a sow of two different breeds. The resulting crossbred pigs are all marketed and the cross is repeated for the next crop of pigs. This system has one disadvantage in that the sows as well as boars have to be purchased and brought into the herd, which can be a means of spreading  diseases.
• Criss-crossing is the alternating use of boars of two breeds on the female stock produced in a herd. For instance, Yorkshire gilts are bred to a Landrace boar. The resulting crossbred gilts are mated to a Yorkshire boar. The next cross is bred back to a Landrace boar, and so on. The gilts and sows, which are sired by a boar of one breed, are always mated to the boar of the second breed. This system of crossbreeding works well and is widely used.
• Crossbreeding can increase litter size (crossbred sows farrow and wean larger litters.), livability (greater resistance to environmental stress) and rate of growth. .

Inbreeding and linebreeding encourage uniformity within the genetic pool and can be used to develop new breeds of pigs. However, as uniformity within the genetic pool increases, the potential for expressing undesirable genes also increases. This in turn can lead to a decline in performance commonly known as inbreeding depression (Buchanan, 2006). Outcrossing and random mating within a breed is used to maintain genetic diversity within a breed of pigs. While breeding like to like can support uniform transmission of superior traits to all offspring, usually some level of inbreeding depression occurs whenever breeds or lines within breeds are kept pure. Thus, crossbreeding is by far the most common form of mating strategy used in the U.S. swine industry because of the advantages of heterosis.

 

Heterosis

 

Heterosis or hybrid vigor is the improved performance of offspring compared to the average of their parents (NSIF, 2003). Heterosis occurs when unrelated lines or breeds of pigs are bred to each other and can be thought of as the recovery of performance depressed by inbreeding in the parent populations. This advantage typically occurs via expanded genetic diversity. Table 1 and 2 summarize heritability and heterosis estimates for important swine production parameters. Heterosis tends to be largest for traits with low heritability such as prewean mortality and 21-day litter weight. For traits with high heritability—for example average daily gain—heterosis tends to be less.

For most farms not raising animals primarily for breeding or show stock, a crossbreeding system is used because it provides significant improvements in traits relating to reproductive performance and mothering ability. Table two presents estimates of heterosis advantage for selected production traits under different breeding scenarios. The values presented in the table are percentages. For example, if a purebred sow was bred to a boar of the same breed and she gave birth to 10 live pigs, that same sow would be expected to give birth to 0.5% more pigs for a litter size of 10.05 pigs if she was bred to a boar of a different breed. Alternatively, if a crossbred sow was mated to a boar of a completely different breed we would expect an 8% advantage over the purebred scenario or 10.8 live born pigs.

Crossbreeding Strategies

Because of hybrid vigor, crossbreeding systems are used on almost all U.S. pig farms. There are several different approaches to crossbreeding that producers may use, each with different advantages and challenges.

Terminal System

One of the most common crossbreeding strategies in the U.S. swine industry is the terminal system.  In this system crossbred females are bred to a terminal sire (either purebred or crossbred) and all the offspring are sold.  This is a simple system to manage, will create genetically uniform groups of pigs from year to year, and captures 100% of available hybrid vigor in the females and all offspring.  The drawback to this system for small and beginning farmers is that you will have to purchase all replacement gilts and boars. Regularly purchasing replacement gilts may be cost prohibitive and increases the potential for introducing novel pathogens into your swine herd.

Rotational Systems

Many small pig farms use a rotational system. In this system boars of selected breeds are rotated into the herd with each generation of replacement gilts. Replacement, cross-bred gilts are raised on-farm which helps support herd biosecurity. Table three summarizes various crossbreeding strategies in terms of complexity and percent heterosis maintained in the offspring. As the number of breeds included in the rotation increases, the amount of heterosis maintained also increases. A rotational system does not allow maximization of hybrid vigor but is a common system due to the potential for lower cost when compared with purchasing replacement animals. If natural service is used a large number of boars (at least one of each breed used in the crosses) may need to be kept on the farm in order to maintain the planned genetic program. Table four provides an example of a three-breed rotation. Historically the cost of purchasing and maintaining multiple boars and the level of record keeping necessary to track each generation of offspring led to most farms settling on a three breed rotation (Ahlschwede, 1988). Using artificial insemination allows a wider variety of boars to be accessed without having to maintain those individuals on site. Today with the availability of purchased semen and personal computing technology some of the barriers to more complex breed rotations have been reduced.

Combination System

There is also the option of utilizing a combination of the two systems. A small subset of the herd is kept in a rotational system that is used primarily to produce replacement gilts for the entire farm. Some of the replacement gilts are kept within the rotational system, but most are bred to a terminal sire with 100% of the offspring being marketed. This combination allows you to raise your own replacement gilts and maximize hybrid vigor in most of the pigs raised for market. For producers managing a small group of sows and gilts, this system can become cumbersome and difficult to manage well. Detailed recordkeeping and management are needed to insure the success of this system.

 

SYSTEMS OF CROSS BREEDING

Two – Breed Rotational Cross

• This system is often called the back cross or crisscross method. Boars of two different breeds are used in alternate generations.
• Crossbred gilts are retained and mated to boars from one of the two-parent breeds.
• The two breeds should complement to each other eg. litter size, growth, carcass characteristic etc.

Three – Breed Rotational Cross

• The three – breed rotational cross is most widely used system. It increases the hybrid vigour by use of three breeds instead of two.
• A third breed can strengthen certain performance characteristic is the crossbred offspring.

SYSTEMS OF FARROWING

• Two litter a year system
  • Advantages: Both fall and spring pigs are raised from the same sow. The pigs can thus be marketed at two different times of the year. The capital investment in building and equipment is made used to the maximum. There is also better distribution of labour and farm income.
  • Disadvantages: The cost of maintaining tried sows throughout the year is high. By the time their useful life is over and their market value may be too low. The pig losses in two litter in a year is more.
• One litter in a year
  • Advantages: In this system gilts are used and pigs are farrowed in spring. As soon as first litters are weaned the gilts are finished to market. Thus the return value of female is more in this system. Other advantages are
    • The management problem is less
    • Less capital is tied up in buildings and equipment and less grain storage is needed
    • The weather is more favourable at the farrowing time and as such pig losses are less
    • The labour requirement is less
  • Disadvantages: The maximum use of available buildings and equipment is not made. The improvement is not as rapid as in the two – litter system since the females are after each farrowing. Moreover the distribution of labour and farm income is not uniform throughout the year.
• Multiple farrowing system
  • This programme can increase the size of the enterprise. The sow herd is split into 2 or 3 groups with each group farrowing twice or thrice in a year. With these groups the farrowing schedule may be as follows.
    • First group: January, July
    • Second group: March, September
    • Third group: May, November
  • In this system there is regular flow of pigs to market, a better use of existing facilities and distribution of labour evenly throughout the year. Two main disadvantages of the system are possibility of frequent disease outbreak and necessity to a competent help for prolonged farrowing.

MANAGEMENT FOR OPTIMAL PRODUCTION

• The fertility of sow and litter size farrowed and weaned are very important factors in determining the viability of swine projects. The cost of raising 6 pigs or 10 pigs from birth to weaning is more or less similar since the maintenance requirement of the sows is the same to both cases. Breeding and selection alone are not very certain methods of improving the production of swine. Time spent on improving the management of the sow and litter, on increasing the efficiency of feed utilization and the control of diseases are parasites may contribute more to the income of the enterprise than an equal time spent to increase herd productivity by following complex method of breeding and selection.
• To ensure that the maximum number of bred gilts and sows farrow large litter of living pigs the following measures are suggested.
  • Gilt may be bred to farrow at 12-14 months of age. Gilts should weigh at least 100 kg before breeding.
  • Gilts come into heat during first few days after weaning. When weaned after 3 weeks breed on the first heat.
  • In hand breeding sows are bred twice during the heat period. Once when they come into heat and again after 24 hours. In pen mating sow may be put with a boar till the heat lasts.
  • The commercial pig may be bred to several boars in the same heat period. 2 boars are run together with the same female in heat or 1 boar for 1 day and second for next. With this procedure the chance of conception will increase.
  • Though the heritability of litter size is low. Selecting for this trait should be continued. In order to increase the litter size by 1 pig we may have to select pigs for this trait for 20 generations.
  • The female selected for breeding must have at least 12 functional and well spaced teats and a good body length.

Breeding gilt to farrow at 12-14 month, two mating within 24 hours of estrus, minimum 12 functional and well spaced teats

• • While selecting the breed for a swine enterprise the litter size must be kept in mind. Yorkshire pigs are on the top in this regard with 10-11 pigs per litter. In most breeds litter size is 9-10 but in few breeds it may be as low as 6-8.
  • If old boars are to be used for breeding, one with a good conception rate with large litters may be used.
  • Both the gilts and sows must be thrifty and in medium condition before breeding, of too fat, the condition may be reduced and if too thin, the condition may be improved.
  • During hot summer months one must keep the breeding and gestating sows cool by water sprinkling or by the use of wallow.
  • Intense inbreeding may be avoided as for each 10% inbreeding there is one-third less pig per litter farrowed and one-half pig less at weaning.
  • Before breeding check the females for brucellosis and leptospirosis. One must avoid breeding sows suffering from flu. During early gestation high body temperature at breeding time may cause abortion.
  • Gilts and sows may be kept in the farrowing stall or pen 5-7 days before due to farrow.
  • A well trained attendant is needed for farrowing. As soon as newborn pigs are dried after removing membranes, it is made sure they breath. Overlying should be prevented. Greatest losses occur with in 3 days after farrowing, so a close watch on the sows and pigs must be maintained during that period. The death may be due to starvation (26%), digestive problem (2%) and unknown cause (13.%).
  • The sow is at her best in milk production at about 3 weeks lactation after which milk quantity is reduced. So a creep feed may be used from 3 weeks till weaning to supplement milk. The ideal weaning weight at 8 weeks age is 15 kg.

Select boar from large litter, avoid inbreeding, checking females for brucellosis and leptospirosis, use of trained attendant to minimize piglet mortality, early introduction of creep feed, aim to achieve 15 kg at weaning

• The farrowing and nursing facilities between groups of females farrowed must be cleaned and kept vacant for at least a week.
• The sow and pigs must be put on ‘clean pasture’. More than 6 sow and litter per lot may not be put on the pasture.

·         EXOTIC / IMPROVED BREEDS OF PIGS

 

Classification of swine breeds based on utility
Lard type	Bacon type
Duroc	Tamworth
Poland china	Yorkshire
Chester white
Berkshire
Hampshire
Spotted Poland china

 

Exotic breeds experienced in India

Large White Yorkshire Middle white Yorkshire Saddle back Tamworth Berkshire

 

Classification based on colour
White breed	Yorkshire , Landrace, Chester White
Black with some white	Hampshire, Berkshire, Poland china
Black and white	Spot
Red breed	Duroc and Tamworth
Red with some white	Hereford

 

The Importance of Reproductive Performance

Livestock farmers generally appreciate the time and input costs required to grow animals from birth to market weight. What is sometimes overlooked is the substantial expense involved with maintaining the mature breeding animals that are necessary to produce any stock for subsequent growing and finishing. Profitability in any commercial livestock-breeding unit is related closely to reproductive efficiency. Unfortunately, some producers and even many of their “expert” advisers pay insufficient attention to this aspect.

No presently available procedure allows prediction of current or future fertility. Thus, accurate monitoring of immediate past performance is essential to identify problems quickly and to initiate solutions before consequences become too severe. Some considerations for the assessment of performance and suggestions for problem solving are presented later in this section.

Boar Selection

• The boars have more impact than the females. Select wisely and carefully.
• Concentrate on performance trait(s) of economic importance and select from source that test or record as many boars as possible (high selection intensity)
• Make certain only healthy replacements selected. This is especially critical if boars are purchased.
• Select for physical soundness: strong feet and legs, watch them walk, no buckling of front legs or stiffness in hind. Boar must have good general conformation and willingness to breed (good libido).

Boar Management

• Feed to keep fit, not fat, usually receive sow gestating diet;
• If purchased, isolate for 3-6 weeks, allow 3-4 weeks to settle in;
• Can use to breed at 6-7 months of age – occasional service;
• Ensure that first mating is successful. Use a small, quiet sow or gilt in good estrus.
• Mating in boar’s pen may be the best location since the male is not distracted by new surroundings.
• Wait until 7-8 months of age before regular use, 2-4 times per week until one year of age.
• Mature boars can perform 6-10 services per week.

Boar to Sow-Gilt Ratios

Natural service – 1 boar for every 20 females

AI + natural – 1 boar for every 20-30 females

All AI – 1 boar for every 40-50 females. Larger herds require fewer boar’s

Gilt Management

• Select from dams with good prolificacy and mothering ability.
• Important traits are sound feet & legs, good growth rate & back fat, 14 or more well spaced teats with none inverted and sexually mature by 220 days of age.
• Within herd selection makes genetic evaluation easier and provides fewer health concerns but must watch out for inbreeding.
• Purchase from other breeder or hybrid producing company simplifies within herd breeding program but should make certain of genetic quality and health status
• Isolate all additions for 3-4 weeks.

Factors Influencing Puberty

Genetics
– Yorkshire and Landrace usually mature slightly earlier than Hampshire or Duroc.
– crossbreeding advances puberty.

Nutrition
– restricted feed intake can delay puberty slightly.
recommend to allow only 0.5 kg gain per day after market weight.
– obesity interferes with normal ovarian function.

Distress
– moving or mixing gilts – fight
– tends to cause puberty 4-7 days later
– contact with boars may advance puberty
– related to pheromones
– direct exposure most effective
– exposure should not be too early (after 155 days of age)
– older boars more effective.

Light
– some evidence for advantage of increase light
– may decrease age at puberty
– may increase litter size

When to mate

• litter size related to number of heats more than age or weight
• fewest ova at first estrus (heat) = smallest potential litter
• increase by about 1 ovum each for 2nd, 3rd heat so potential litter size increases
• normally breed in 2nd or 3rd heat so gilts farrow by 10-11 months of age.

Mating gilts on the third observed estrus resulted in larger litters but also required feeding the dams for an additional six weeks. Depending on costs for feed and housing, the extra piglets may or may not compensate for the additional expenses.

Pregnancy rates were 69.6% for animals bred at first estrus and 77.4% when mated at the third estrus in the study conducted by Young and King. Although this difference was not statistically significant in this trial, subsequent experience also indicated a somewhat lower fertility at the first cycle. An even lower pregnancy rate is usually obtained in the University of Guelph research herd when sexual maturity is induced with hormone injections (about 55% for six month old gilts inseminated on the induced estrus vs. 80% in sows).

Perhaps the best practical advice for producers is to wait for the second or later heat whenever this is convenient. However, if replacement animals are needed to fill groups and no older females are available, gilts can be mated on their first estrus. If gilts are mated at the first cycle, use herd boars rather than expensive semen purchased from an outside supplier.

Estrous signs

• Swelling, reddening of vulva – not positive
• Ears erect (especially in Yorkshire breed)
• Standing reflex – response to pressure on back (see Back Pressure Test described below). Boar presence may be necessary, especially for gilts
• Allows mounting and copulation
• Characteristic grunt (or song)

Good Practices for Detecting Estrus

• Use a sexually motivated boar in an adjacent pen or introduce the boar directly into the pen containing the females to be tested.
• Boars used for estrus testing should be 9 months of age or older.
• Be certain that the boar is familiar with and comfortable working in the testing environment.
• Allow sufficient time to do a thorough job in all pens.
• Change boars regularly.
• Allow no more than 15 – 20 seconds of vigorous courtship.
• Supervise the testing procedure at all times.
• Keep accurate records of weaning, suspicious and actual mating dates.

Back Pressure Test

• Whenever possible, allow boar and females to have head-to-head access through pen partition or gate.
• If in or very near estrus, a female should show definite interest in the boar almost immediately.
• Rub the interested female’s flanks and scratch her back.
• Gently put firm pressure on loin region or sit on her rump. Animals in estrus will allow this but others will not. A positive response is when any female stands still and allows the tester to place full weight on her back, Gilts may only respond if a boar is near. Most sows will show a positive response anytime that they are in estrus.
• Retest any animals showing suspicious signs in a few hours.

Mating Practices

• Group recently weaned sows and replacement gilts near boars.
• Design all pens for easy access to facilitate entry and exit of both people and animals during estrus detection and mating.
• A proper mating area requires ample space for all courtship and mating activities.
• Provide nonslip footing with roughened concrete and sand or grit spread as needed.
• Remove any objects or projections, such as feeders or nipple drinkers, that might cause injury during courtship-mating.
• Try to mate animals of approximately equal sizes.
• It is perhaps best to move the female into the boar’s pen for mating since she may be easier to get out after the mating.
• Supervise all matings to insure that the boar’s penis penetrates into the vagina, not into the anus.
• A proper mating-ejaculation sequence should last at least three minutes. If shorter, repeat the service.
• Remove the female quickly after the boar dismounts unless the copulation was interrupted before three minutes.
• Always be gentle when handling animals.
• Record all events accurately and quickly.

Timing & number of services

• Ovulation occurs about 36-40 hours after the beginning of standing heat
• Optimum insemination is 6-12 hours prior to ovulation
• Therefore, mate 24 hours after initiation of standing heat and rebreed 8-16 hours later if female will still accept the boar or is still showing a positive (standing) response to the Back Pressure Test.
• A different boar might be used at each service if breeding only for market pigs.

Feeding Replacement Gilts

• If gilts are placed on a restricted level after selection, increase feed intake by 50% 10-14 days before breeding. This process, called flushing, might increase ovulation rate.
• If flushed, reduce feed intake after breeding
• Some believe that heavy feeding during early gestation increases embryonic loss but most evidence indicates that this is not true!

Housing for Breeding Females

• Group housing is preferred.
• Tethering or over-crowded confinement hampers breeding ability through difficulties in detecting estrus

Pregnancy Diagnosis

Sows and replacement gilts require considerable attention in the mating area but only casual observation once they are pregnant. Thus, producers usually place pregnant females in a gestating area but need some reliable method to check that conception occurred before animals are moved from the mating unit. All attendants should be aware that domesticated animals rarely exhibit any signs of sexual behavior one cycle interval after a fertile mating. Thus, for animals mated on known dates, demonstration of sexual receptivity when the next estrus period is due indicates no conception from the previous service. In contrast, the absence of sexual behavior is strong evidence for pregnancy. Sows and replacement gilts should remain in the mating area, with daily boar contact to check for estrus, for around 25 days after service. Once they pass three weeks without estrus signs they can be presumed pregnant and moved to the gestating area.

Other methods for pregnancy testing are also available.

Livestock producers must recognize that there is one inherent problem that will continue to be associated with even the most reliable pregnancy test. No matter how accurate the procedure, the results are only valid for the time when the sample was collected or the physical examination conducted. There can be no guarantee that the embryonic or fetal piglets present at the time of testing will continue to develop normally throughout the remainder of gestation.

Early Embryonic Mortality

Unless fertility depressing abnormalities or mistimed matings occur, fertilization rates in pigs approach 100% so almost all ovulated oocytes have a chance of developing into viable piglets. Unfortunately, a substantial proportion of these early zygotes do not successfully complete gestation and this is a major cause of reduced litter size. Most of the losses occur during the first 3 to 4 weeks and are designated as early embryonic mortality. When death occurs at this very early stage of pregnancy, the conceptus is resorbed completely in the uterus so losses remain undetected. Some embryonic mortality undoubtedly results from chromosomal abnormalities present in one or possibly both fertilizing gametes. Abnormal karyotypes have been detected in a high proportion of aborted human fetuses but not in those from domesticated mammals. This might infer that chromosomal defects are relatively unimportant in livestock. However, the livestock conceptus may be lost at very early stages before karyotyping is possible, or the damage could be at a submicroscopic level. Some degree of embryonic mortality must be considered unavoidable and represents a natural mechanism for elimination of unfit genotypes but the extent of this in livestock is uncertain.

Preparation for Farrowing

• Follow an All-In All-Out system.
• Treat females with anthelmintic about 3-4 weeks before they are due.
• Feed a laxative diet for the week before moving into the farrowing crate or pen.
• Thoroughly clean and disinfect all farrowing crates between occupants
• Wash the sow thoroughly to remove dirt and parasite eggs and place in the farrowing location about one week before her expected date of parturition.

Seasonal Influences on Pig Reproduction

Wild pigs are seasonal breeders, usually mating in the late fall and giving birth to piglets in early spring. Although selection over many generations has almost totally eliminated any seasonality of reproduction in domesticated pigs, some traces still remain. Close observation of large groups in several countries indicated slightly longer intervals from weaning to estrus, more animals not returning at all within a reasonable interval, and lower prolificacy in animals weaned during late summer and early fall. This infertility has been attributed to higher temperatures in some regions and undoubtedly this may be a factor in tropical climates. Producers wishing to insure they have sufficient pregnant animals to keep farrowing units operating at full efficiency should always cull a few less sows and keep a few more replacement gilts during the summer and early fall.