Techniques of  Artificial Insemination (AI)  in Goats for Higher Production

Techniques of  Artificial Insemination (AI)  in Goats for Higher Production

Artificial insemination is a technique whereby semen collected from the buck is deposited by an AI service provider in the right place in the reproductive tract of the doe at the appropriate time. Usually the semen used is processed. After collection and evaluation, the semen that meets the required standards is extended to increase its volume so that it can give many breeding doses. Semen extension involves use of semen diluents or extenders that will nourish the spermatozoa and provide a good environment for their survival. The volume of extender added to the semen is worked out in such a manner that the resulting doses obtained from each ejaculate will contain a sufficient number (i.e. at least 20 million spermatozoa in each straw at the time of freezing, with at least 8 million being alive post-thaw) to cause fertilization. After extension the semen is packed, commonly in straws, and can be used fresh within a few hours, chilled for use within a few days, or frozen in liquid nitrogen for use even after many years. The standard procedure for inseminating does involves raising the rear quarters of the doe, with the forequarters on the ground, and with the help of a speculum and light source, locating the right position and depositing semen into the female reproductive tract.

Artificial Insemination (AI), defined as the process of introducing sperm from superior male animal into the female reproductive tract for the purpose of impregnating the female using artificial means (AI gun). AI can undoubtedly be regarded as the oldest and most widely used Assisted Reproductive Technology (ART) and has made the most significant contribution to genetic improvement worldwide . The effectiveness of AI is counterbalanced by constraints arising from the reduced number of males, decrease in genetic variability, possible dissemination of genetic defects and an increase in the inbreeding coefficient affecting the maternal traits. The preservation techniques using chilled or cryo preserved semen of genetically top-quality male animals make the application of AI in breeding programmes more efficient and flexible . However, studies have revealed that preservation techniques induce sub-lethal damage that affects the functional capacity of spermatozoa, as a result of which they behave differently from fresh spermatozoa even if they are fertile. Irrespective of the type of extender/diluent or the technique of storage used, a significant number of spermatozoa show reduced motility and viability (longevity) and decreased fertility with increased length of liquid and frozen storage. Artificial Insemination (AI) has an important role in goat breeding, especially in intensive systems of production, to control reproduction and, in conjunction with accurate progeny testing, to improve the production of milk, hair and meat . Artificial Insemination of goats is generally very similar to that of sheep. However, it is much easier to achieve an intrauterine insemination via the cervix in goats than in sheep, since, the caprine cervix is relatively easier to traverse than the ovine cervix .

The advantages of using AI for breeding include:

• It increases the rate of genetic improvement through maximal use of genetically superior bucks.
• • It increases the number of does to which a buck could be bred, as a single ejaculate can be extended into several breeding doses.
• • It enables introduction of new genetics whose availability may be limited by geographical location. Processed semen is light and can be transported across a long distance.
• • It reduces the risk of sexually transmitted diseases by eliminating natural mating.
• • It eliminates the cost of keeping a buck and the nuisance of having a buck in a herd •
• It is possible to accurately time when kiddings will occur since the breeding dates are known. This enables planning for presence of assistance during delivery if it will be needed.
• • If accompanied by good record keeping, it allows for more accurate pedigree recording in a herd.

Disadvantages of AI:

• The AI equipment are expensive and liquid nitrogen is not available everywhere
• • There will be increased labor costs for heat detection and insemination.
• • There is potential for rapid spread of undesirable traits, if bucks from which semen is sourced are not carefully evaluated. Since a semen from a superior buck can be used to breed many does and even across borders. If the buck had a genetic defect this will be widely spread in the population.,
• • If not well executed (i.e correctly timed, semen quality ascertained and qualified technician used), there is possibility of low pregnancy rates compared to natural mating.

The success of any AI program is largely dependent on three primary factors:

1. Use of viable semen.

This is achieved by sourcing semen from reputable sources and proper handling and use of semen and the liquid nitrogen tank.

2. Appropriate timing of insemination relative to oestrus. If the doe is inseminated too early (before ovulation) or too late (after ovulation), the result will be low conception rates. It is important to try and establish at what stage of oestrus the doe is in prior to inseminating her. This can be done by establishing when the doe was first seen on heat by critically interviewing the farmer/herdsman, and also by examining the mucus in the anterior vagina using a speculum and light source. Clear, thin, mucus is indicative of a doe that is early in oestrus. Cloudy mucus indicates a doe towards the end of oestrus. White or pale yellow thick/cheesy mucus indicates a doe coming out of oestrus. 3. Proper deposition of semen in the doe’s reproductive tract. During natural mating, semen is deposited inside the vagina next to or around the opening of the cervix.

However, during AI, semen is deposited within the cervix or uterine body. Processed semen is diluted and a smaller volume is used. One of the reasons for low conception rates in goat AI is deposition of semen in the anterior vagina of the doe. Therefore, for good conception rates, the AI gun should be passed through the cervical opening (os cervix) for the semen to be deposited in the cervix or uterine body. Not every doe presented for AI must be inseminated. Only does that are in good health (body condition score of 2.5 to 3 on a scale of 1 to 5), are on a rising plane of nutrition, free from diseases, and good mothers should be bred using AI. Does that do not have regular cycles or those which are difficult to determine when or if they are in oestrus should not be bred by AI, but rather by natural mating.

Techniques of Caprine Artificial Insemination

 

Various techniques of inseminations can be successfully used in goats which includes intravaginal, trans cervical and laparoscopic with comparable fertility results by using fresh, chilled and frozen semen .

1. Vaginal AI (Peri-cervical insemination) ———–The technique involves the semen deposition in the cranial vagina (deepest point/fundus of the vagina) without attempting to locate the cervix (no visual source is used). The ideal timing of AI is before ovulation, i.e. 12-18h after onset of estrus. The volume of semen and the minimum number of progressively motile spermatozoa that are recommended to be used are 0.2ml and 400×106, respectively. Intravaginal AI is effective in the doe while using fresh semen, but gives poor results with extended (chilled) or frozen semen . Intravaginal AI is best suited to use after estrus detection during the natural breeding season.
2. Trans – cervical AI (Intra-cervical insemination)

Intra-cervical AI is the preferred option in small r u m i n a n t s , w h e n t h e e x t e r n a l o s i s located/visualised using illumination. This method can be used with fresh and chilled/frozen semen. The ideal time for AI is 15-17h after the onset of detected estrus . Frozen semen can be used with cervical AI, but with reduced conception results which might be associated with the reduced viability of frozen spermatozoa that resulted in low numbers of viable or undamaged spermatozoa reaching the fertilization site. The inseminate volume and the minimum number of motile spermatozoa required are 0.2ml and 200×106, respectively.

3. Trans-cervical Intra – uterine AI

Trans-cervical intrauterine AI techniques also known as Guelph system of trans cervical AI. The technique requires special positioning of the animal, cervical retraction and the use of specially designed instruments for the stabilization and passage of the insemination pipette through the cervix. The inseminate volume (0.2-0.5ml) and minimum safe number of motile spermatozoa (60×106 per insemination dose) can be injected between 49-65h after the removal of progesterone inserts. Semen should be deposited in the body of the uterus, although cranial cervical deposition has also yielded satisfactory results . Certain drawbacks are associated with this technique which includes; cervical injury, abscesses, infections and poor pregnancy rates all of these varies with operator expertise, semen dose and physiological condition of doe.

4. Laparoscopic Intrauterine AI Recent advancements with regards to usage of AI in small ruminants is the development of laparoscopic intrauterine insemination. In this technique, the semen is directly deposited into the lumen of the uterine horns at a point closer to the site of fertilization . So, by using this technique it is possible to bypass the cervical barrier and decrease the amount of semen used for AI. The minimum safe number of motile spermatozoa is 20×106 per insemination dose, and the ideal timing of AI is between 48-65h after the removal of progesterone inserts . Conception rates (60- 75%) achieved with frozen semen using this method are higher than intracervical insemination. The major disadvantages with this technique includes, need for expensive laparoscopic equipment, invasive surgery and the technical expertise needed to perform the procedure. Since, laparoscopic intrauterine AI is banned in most of the North European countries and hence special attention has been paid to cervical AI with frozen semen .

 

Estrus, Estrus Signs and their Detection

Sexual receptivity in the female is expressed in a short period of time known as estrus. Females undergo behavioral changes during the estrus period indicating sexual excitement and receptivity to the male. The signs of estrus are primarily changes in behavior, one or more of which may be exhibited by most does which includes, increased frequency of bleating, frequent urination, obvious restlessness or an increase in doe interaction, tail flagging, increased curiosity and attentiveness to the flock handler, exhibition of mounting behavior by does, receptivity to mounting (standing heat), and anatomic changes including swelling of the vulva, discharge of vaginal mucus and hyperemia of the vulva etc. . Behavioral manifestations along with anatomic changes are the best tools to schedule the time of mating either by natural service or by AI. When bucks are available, does actively seek males when they are in estrus. Bucks odour seems to have a stimulatory effect on does. The most dependable sign of estrus is the doe’s response to a buck . A doe will remain immobile for breeding only during this period of standing heat, which lasts from 12 to 48h (Average 36h) . Successful AI requires that human judgment be substituted for a buck’s instinct and libido. Does should be observed at least twice a day (early morning and late night; cool hrs) when the animals are free from distractions. Different practical methods of estrus detection are used, including use of entire males, vasectomized males or androgenized females fitted with an apron harness and marking crayons. These ‘teasers’ may be run with the flock and marked does removed once or twice per day, or they may be taken to the females at regular intervals and their behavior observed directly. Pregnancy rates in goats following AI after cervical or trans cervical insemination with frozen semen vary from 7–79 percent in different breeds of goats . Chilled and frozen-thawed semen is used for insemination in natural, synchronized or induced estrus in which several factors can influence the fertility. In majority of the studies, season, breed, age of goats, estrus synchronization protocol, time and number of AI, body condition score and the breeding technology per se have been the reported for variable fertility results.

Factors Influencing Fertility

1.Type of Estrus (Natural / Synchronized / Induced estrus) Successful AI depends on an efficient management of estrus detection. Sexual receptivity of the female is evidenced by the postural immobilization of the female in response to mounting by the male. In order to control the time of onset of estrus in the normal breeding season, simple technique of male segregation and reintroduction have been employed to synchronise oestrus and ovulation called as “buck effect”.In large commercial herds, economic considerations necessitate the synchronization of estrus in females which are cycling naturally, or its induction during the nonbreeding season, with insemination performed at a fixed time either in relation to the beginning of estrus or the end of a hormonal (PMSG) treatment . The hormonal treatment generally used to induce estrus and ovulation is based on combinations of progesterone or a progestogen treatment followed by ECG and may include treatment with commercial melatonin and prostaglandin analogues .Nonhormonal techniques of estrus synchronization may also be employed which includes, flushing up, buck effect and photo period management. Due to the ease of use and availability, the Controlled Internal Drug Releasing Device (CIDR) has become the gold standard for progesterone delivery in sheep and goats . Estrus in animals treated with CIDRs typically occurs within 48h after withdrawal of the device . Administration of eCG can induce ovulation in ewes and does during anestrous .

 

2. Characteristics of Individual Animal

Irrespective of the process used for freezing, differences have been observed between males regarding the freezability and fertility of semen. This variability is relatively independent of prior semen quality and the semen of certain individuals consistently freezes with less cryo injury than that of others. Spermatozoa acquire cold shock sensitivity as they traverse the epididymal tubules and this variability is believed to be related to changes in membrane lipids during the epididymal transit. Sperm mixing in the epididymis may provide a potential mechanism for variability in response to subsequent temperature fluctuation, in their response to freeze-thawing.

 

3. Season of Semen Production

Reports on the freezability and fertility of semen collected in the breeding and non-breeding season are contradictory. Some investigators found that freezability and fertility of frozen-thawed spermatozoa was better when collected in the breeding than in the non-breeding season and recommended its long-term storage during the normal breeding season . Contrarily, other workers  observed no seasonal difference on fertility. Temperature has been suggested as major factor affecting the seminal quality parameters in both Gaddi and Chegu breed of goat during breeding season.

4. Physiological Condition of Females

The physiological condition of the doe varies with parity, season, level of production and age. Therefore, all these factors have been influencing the success of hormonal treatments to induce estrus synchronisation and ovulation for the subsequent AI . Fertility after estrus synchronisation and AI is low during postpartum and lactational anestrous. The time between kidding and re-breeding affects the fertility of goats.

5. Age and Parity

After hormonal induction of estrus, nulliparous goats were less fertile than primiparous or m u l t i p a r o u s g o a t s w h e n i n s e m i n a t e d intracervically. Maiden goats should be inseminated via laparoscopic method rather than cervical method because of the difficulty in opening the vagina with a speculum.

6. Volume of Inseminate and Number of Spermatozoa

The total number of spermatozoa inseminated per female is one of the main factors affecting fertility, and it is necessary to know the threshold at which the required fertility is obtained for a given breed with females synchronised by particular methods for various conditions of semen storage. The optimal number of sperm per inseminate depends on the fertility of the sire, inseminator competence, and the timing of insemination relative to ovulation. Laparoscopic insemination directly into the uterine horns requires fewer sperm than trans-cervical insemination into the uterine body. Greater number of sperms are required for either cervical or vaginal insemination . As a result, most goat semen processors package goat semen in concentrations that yields 50 to 100 million progressively motile sperm cells after freezing and thawing (3, 5)or in other words initial pre-freeze concentrations should be between 200 and 400 million per milliliter of extended semen.

 

7. Site of Semen Deposition

Another important consideration with respect to sperm numbers has to do with the site of semen deposition. It is likely that many failures in goat AI are the result of misplaced semen. Semen should be deposited in the body of the uterus, although cranial cervical deposition has yielded satisfactory results. Gauging the depth of AI gun penetration by marking the gun as well as developing the proper “feel” when applying pressure to pass the AI gun through the cervical rings should improve AI success rates . Comparisons between laparoscopic and cervical inseminations in dairy goats have shown significant differences in fertility rates (62.6% vs 49.3%), regardless of the low numbers of total spermatozoa deposited.

8. Importance of Timing in Artificial Insemination

Does do not ovulate until late estrus or shortly after the end of standing estrus. Generally, the timing of AI varies according to the AI method used, the nature of estrus (spontaneous or induced), the type of semen (fresh diluted/ undiluted or frozen), the age and breed of the animal, and whether single or double AI is to be performed. For optimal result does should be inseminated during the latter half of standing heat or shortly after the end of standing heat . Quite often, goat breeders follow the am:pm rule as used in breeding cattle. Also, best practice is to inseminate at least 12h after the first observation of heat, with preference for late rather than early insemination .

9. Inseminator Competence and Training

An inseminator competence in handling and placement of semen within the reproductive tract of does play a crucial role. It should be clear that frozen semen may be of excellent quality when it leaves a buck stud or AI facility, fertility will be poor if semen is improperly handled or deposited in the wrong place at the wrong time . Care must be taken to prevent loss of sperm in straws or AI gun. It has been observed that rapid expulsion (2–3s or less) of semen from AI gun resulted in 27 per cent semen residue remaining in the rod, which translates to loss. He suggested that slow and steady expulsion of semen over a period of 5–7s while insemination can minimize the loss associated with rapid expulsion.

In conclusion, timing between semen deposition and ovulation is an important factor in obtaining good conception results. Deeper the semen is deposited in the genital tract, a higher rate of pregnancy is obtained, greater still when the catheter reaches the uterus. This is more justified when frozen-thawed semen is used in comparison with chilled semen and no effect was observed with fresh semen. Preference of insemination technique depends upon type of semen (fresh/chilled/frozen), volume and dose of inseminate to be used for breed conservation and genetic propagation. Fresh buck semen using, vaginal (peri-cervical deposition of semen) and cervical (intra-cervical deposition of semen) AI techniques result in acceptable pregnancy rates if the appropriate volume of inseminate dose and number of spermatozoa are used. However, Laparoscopic intrauterine insemination or Trans-cervical intrauterine AI resulted in acceptable pregnancy rates when using frozen semen.

Oestrus synchronization

Oestrus synchronization is the manipulation of the estrous cycle of does so that many can come on heat at the same predicted time, or a doe so that she comes on heat at a predictable time.

 

Advantages of oestrus synchronization include:

• It improves the accuracy of prediction of oestrus as heat is expected to occur within a specified time period.

• It makes heat detection easier as observation for heat signs can be concentrated at the specific period within which it is expected to occur, and not every day. This will cut down on the time and labor costs of frequent heat observation.

• It improves the efficiency and cost of AI as many synchronized does can be inseminated at the same time by the same inseminator. When an AI technician serves many does in the same area around the same time this will cut down on the cost of each insemination due to economics of scale. The AI will also be more efficient as determination of the stage of oestrus in inseminated does can be more easily established than in those that come on heat naturally. • It can enable fixed-time AI.

Oestrus synchronization, especially under intensive goat production systems, can utilize protocols that enable AI to be done at a specific predetermined time following a synchronization treatment irrespective of whether the does are seen on heat or not. This saves on time and cost of heat observation.

• It can allow for clustered kiddings thus enable more efficient herd management and market access:

• Several young kids born around the same time can be more intensively taken care of for limited periods, as opposed to all year round when kiddings are not controlled.

• Kidding can be synchronized to occur at specific times to coincide with market needs for example when there is feed availability for the dam and young for milk production and growth, or market demand for goats. Different methods are available to synchronize oestrus in does.

These include:

• Use of exogenous hormones

• The male/buck effect.

 

Hormones for estrous synchronization

Two hormones, progesterone and prostaglandin F2α (PGF2α) are the primary hormones used for oestrus synchronization. However, other hormones such GnRH have been incorporated in various protocols.

Progesterone

It mimics the function of the corpus luteum by preventing hormonal activity that controls the estrous cycle. Progesterone blocks the secretion of FSH and LH from the pituitary gland and therefore follicles do not develop and grow on the ovary, consequently blocking the estrous cycle. It is administered for a number of days and then discontinued. Once discontinued, the block it had on FSH and LH secretion is removed. The decreased progesterone concentration results in the release of FSH and LH, follicular development and maturation in the ovary, and oestrus can be expected in 24 to 36 hours of removal.

It can be administered as:

• Vaginal sponge. It is put in the anterior vagina of the doe.

• A Controlled Intravaginal Drug Release (CIDR) device.

A CIDR is a plastic device that contains progesterone. These devices are usually used in conjunction with GnRH and PGF2α. The CIDR is inserted in the doe’s vagina for 8 to 17 days following the injection of PGF2α. As long as the CIDR is in place it releases progesterone into the bloodstream of the doe. When the CIDR is removed, there is rapid fall in progesterone level, much as progesterone falls in the normal cycle, and the does come on heat within 72 hours.

Implant.

It is put below the skin in the ear or tail.

Prostaglandin F2α for oestrus synchronization

It causes regression of the CL, resulting in removal of the negative block progesterone has on FSH and LH release. When this progesterone block is removed, follicles develop, mature and the does come on heat within 36 to 72 hours of administration. It is given as an injection. It is cheaper than using progesterone. However, it only works when there is a responsive CL on the ovary, and this limits its use as there are periods within the estrous cycle when it will not be effective. Two doses of PGF2α 11 days apart will synchronize a group of does. Prostaglandin has to be used with care as it can cause abortion in pregnant does.

The male/buck effect for oestrus synchronization

The buck can be used to stimulate oestrus activity in does that have been previously isolated from bucks. After a period of separation, the buck is suddenly introduced into a group of sexually mature does. Many does may come into heat within 3 days of buck introduction.

DR RAJKISHORE PRASAD, MAGADH AI SERVICES, NALANDA