Techniques for Artificial Insemination of Goats

CHAPTER 68 Techniques for Artificial Insemination of Goats

Artificial insemination (AI) involves placement of semen from a male into the reproductive tract of a female by mechanical means rather than by natural mating. A thorough understanding of the various components of an AI program is very important to goat breeders if the herd is to be handled effectively and efficiently. This chapter is designed to provide readers with a foundation to build a sound AI program.

ADVANTAGES OF ARTIFICIAL INSEMINATION

The contribution of AI to the genetic makeup of highly productive strains and breeds of cattle during the past 40 years has made AI a desirable tool for genetic improvement in other species. AI offers goat breeders the potential for use of genetically superior sires. It enables the small herd owner to obtain breeding services at a reasonable cost. By means of AI, breeders are able to identify superior animals that possess desirable traits. The mating of outstanding sires and dams, even miles apart, may be effectively performed by AI using frozen semen. Such matings have the potential to create desirable new lines, reduce inbreeding, and reduce spread of disease by minimizing animal movement. When used correctly, AI has a number of benefits, including maximal use of outstanding sires, increased herd uniformity, elimination of bucks on the farm, relatively inexpensive semen costs, decreased potential for venereally transmitted diseases, and improved herd management.

DISADVANTAGES OF ARTIFICIAL INSEMINATION

The disadvantages of using AI should also be understood and carefully examined before the herd manager decides on this program for a herd. These include initial costs for AI equipment and nitrogen refrigerator, increased labor for heat detection and insemination, lack of standardized procedures for packaging and quality control for goat semen, lack of suitable sire proofs for production traits, requirement for specialized training because of anatomic constraints associated with the size of the goat, and potential for spread of less desirable traits.

SIGNS AND DURATION OF ESTRUS

The signs of estrus are primarily changes in behavior, one or more of which may be exhibited by most does. It is important to become familiar with and to record these signs for individual does, including time of onset, duration, and intensity. These signs are valuable pieces of information that can be used to determine optimal time for natural mating or AI. Signs include increased frequency of bleating, frequent urination, obvious restlessness or an increase in doe interaction, tail flagging, increased curiosity and attentiveness to the herd handler, noticeable change in milk volume in lactating animals, exhibition of male behavior by does (mounting, snorting), receptivity to mounting (standing heat), and anatomic changes including swelling of the vulva, discharge of vaginal mucus, and hyperemia of the vulva.

ESTRUS DETECTION AND ARTIFICIAL INSEMINATION

One of the most important, if not the most important, aspects of goat breeding when hand mating or AI is used is proper detection of estrus. Because the noticeable signs of estrus are primarily changes in behavior, familiarity with the normal behavior of individual does is required. These behavioral changes along with anatomic changes are the best tools to use to time mating either by natural service or by AI.

When bucks are available, does actively seek males when they are in estrus. The odor of bucks 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 48 hours. Successful AI requires that human judgment be substituted for a buck’s instinct and libido. If a person is less diligent or conscientious in the task of detecting heat than the buck, then some does in estrus will be missed and not mated.

Herd management conditions determine the exact procedures to be followed in observing for signs of heat. Does should be observed at least twice a day when the animals are free from distractions. Lactating animals can be observed shortly after each milking. Open, nonlactating does in loose housing or at pasture must be observed carefully. These animals may have to be confined twice daily. Choosing the right time of day (early morning and late night when it is cool) and location (shade, water source, near buck pens) will help tremendously.

Nothing helps detection of does in heat as much as accurate animal identification such as tags with large numbers or clear brands, and a record-keeping system that indicates when particular animals require observation. Individual doe cards and large calendars are often used to keep simple “heat due” dates.

IMPORTANCE OF TIMING IN ARTIFICIAL INSEMINATION

It must be understood that a doe is fertile only when an ovum is present that can be fertilized. Likewise, it must be understood that ova are viable for only a short time after being ovulated unless they are fertilized. Does do not ovulate until late estrus or shortly after the end of standing estrus. Therefore, for optimal results does should be inseminated during the latter half of standing heat or shortly after the end of standing heat.

The accuracy of recognizing the signs of standing heat is at best fair and is generally reflected in the success of AI. Quite often, goat breeders follow the AM:PM rule used in breeding cattle; animals first noticed in heat in the morning are bred in the afternoon and animals first noticed in heat in the afternoon are bred the following morning. Although this system works moderately well, it is no substitute for exact information regarding individual estrous behavior and length. The author’s personal preference is to inseminate at least 12 hours after the first observation of heat, with preference for late rather than early insemination, provided that animals are checked regularly at least twice a day at 12-hour intervals. This preference is based on information available regarding the time of ovulation, duration of sperm transport in the female reproductive tract, and time of survival of male and female gametes.

AIDS FOR SUCCESSFUL HEAT DETECTION

A number of aids have been developed to assist with the task of detecting does in estrus. These include the use of a “buck rag,” which is a cloth that has been wiped over the scent glands of a male in rut, stored in a closed jar, and warmed before opening in the presence of the does; a sturdy and secure buck pen with a breeding window in an area where does are brought in for heat detection; the use of sexually altered (by penile deviation or vasectomy) males fitted with a marking harness; use of wethers or intact females treated with testosterone; and the use of intersex goats or hermaphrodites.

HANDLING OF SEMEN

The procedures used for handling semen, beginning from the time it is shipped from the supplier until it has been deposited in the doe, have a tremendous influence on fertility. Low temperature enables semen to be stored for extended periods of time once it has been frozen, but the fact that semen remains frozen does not ensure that fertility has been maintained. Damage can be expected any time the temperature of frozen semen rises above −130° C, and the rate at which semen deteriorates increases as the temperature rises. Although liquid nitrogen has a temperature of −196° C, the potential for damage due to elevated temperatures is present when semen is transferred between tanks and when semen is elevated into the neck of a tank so that some can be removed for thawing. A current inventory of the location of semen within a storage tank and use of procedures to minimize both the extent of warming and length of time semen is exposed to elevated temperatures during routine handling are essential to maintenance of high fertility. Thawing techniques differ between ampules and straws, and among various types of straws. Research on thawing semen in ampules or straws has concluded that semen in ampules should be thawed in ice water while semen in straws should be thawed in water at about 35° C.

Although most researchers now recommend that semen in straws be thawed in water at about 35° C, controversy exists as to whether the semen should remain in the thaw bath until its temperature has reached the temperature of the water or whether thawing should be timed so that the semen temperature does not rise above 5° C. Recent work on cattle semen in a large trial concluded that thawing need not be timed to prevent semen temperature from rising above 5° C, and that fertility may actually be improved by allowing semen temperature to rise to 35° C.

Another controversial issue, with respect to semen in straws, is the importance of using the semen immediately upon thawing. Although most cattle AI organizations recommend that thawed semen be used as soon as possible, they have expressed little concern at allowing semen to remain in the thawing bath for several minutes. In goats, however, it is recommended that semen be thawed for 30 to 60 seconds at 35° C because of the likelihood that the semen will spend several minutes in the doe’s tract while the inseminator tries to penetrate the cervix.

NUMBER OF SPERM PER INSEMINATE

The number of sperm per inseminate is an important factor influencing the fertility of frozen semen. The optimal number of sperm per inseminate depends on the fertility of the sire, inseminator competence, and the timing of insemination relative to ovulation. Goat semen processors are best qualified to determine the optimal numbers of sperm cells based on client feedback. Few field trials titrating sperm numbers against conception rates have been conducted for goats. As a result, most goat semen processors package goat semen in concentrations that yield 50 to 100 million progressively motile sperm cells after freezing and thawing. With suitable processing and careful handling and thawing, at least 50% of the cells survive and are progressively motile. Thus, initial prefreeze concentrations should be between 200 and 400 million per milliliter of extended semen. Semen from certain sires survives freezing, storage, and thawing better than semen from others, for unknown reasons. Thus, knowledge of individual freezing ability of semen is essential for deciding how many sperm are necessary for each breeding unit.

Another important consideration with respect to sperm numbers has to do with the site of semen deposition. Laparoscopic insemination directly into the uterine horns requires fewer sperm than does transcervical insemination into the uterine body. Greater numbers of sperm are required for either cervical or vaginal insemination. Whatever the site of insemination, the number of motile spermatozoa in the inseminate affects fertility. Generally, less fresh extended semen will be needed than frozen-thawed semen. A recommended safe limit for the number of motile spermatozoa is shown in Table 68-1.

Table 68-1 Minimum Safe Numbers^* of Motile Spermatozoa for Insemination at Different Sites

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Sep 3, 2016 | Posted by admin in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off

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