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United Suffolk Sheep Association |
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Glen Erickson Shepherd at Utah State University, AI Technician AI in the Sheep Industry Today INTRODUCTION Over the past few decades, advances in genetic improvement from the use of artificial insemination in many species of livestock including, cattle and hogs has benefited in significant economic gain. The increase in the gene pool alone will have a long lasting and major influence on these two industries. The sheep industry however has not experienced the same influx of superior genetic improvement. For many years artificial insemination of sheep was thought to be impractical due to the lack of a simple and effective method of artificial insemination. Today however, artificial insemination (AI) is gaining acceptance in the sheep industry. To understand the drawbacks that limit the use of AI in sheep we must look at the anatomical structure of the ewe’s cervix, which is small and difficult to navigate. Unlike the cervix of a cow or that of a hog that can be penetrated effectively with a little practice, the cervix of the ewe has many annular folds and misaligned rings rendering it very difficult to manipulate and penetrate. Some recent advancement in this area of cervical penetration has shown great promise, but has proven to be yielding unacceptable conception rates. There are several other factors contributing to low conception rates and the limited use of AI in sheep including heat detection, and the use of frozen semen. With the use of hormones such as progesterone and PMSG (pregnant mare serum gonadotropin) synchronization of the ewe’s estrus (heat cycle) can be successfully controlled. For acceptable conception rates, a minimum number of sperm cells (normally exceeding 200-400 million live sperm) must be used when sperm is deposited in the cervix. During the freezing and thawing process nearly 50% of the total sperm cells die. Even with recent advancements in semen cyropreservation (freezing), and improved methods of heat detection, AI in sheep has gained only limited acceptance among purebred sheep breeders and is practically nonexistent in the commercial sheep industry. Over the years, many different methods of artificial insemination have been tried in sheep with some degree of success. Three methods have proven useful and are currently being used through the world with varied success:
METHODS OF ARTIFICIAL INSEMINATION Three methods are most commonly used in sheep. 1. Vaginal insemination. Sometimes called a “shot in the dark” (SID) method. With this method fresh or fresh chilled semen is s imply deposited in the anterior vagina. Results can be as good as (40% to 60%) conception when adequate numbers of sperm are used up to 12-16 hours following collection. Frozen semen is not often an option here, as it does not produce acceptable pregnancy rates when deposited vaginally. The SID method can be used successfully in a management program to extent your ram power by breeding a large number of ewes the same day. Semen is collected, extended and deposited in a large number of ewes, (10-100) resulting in far more ewes bred than the ram could serve naturally in a single day. Lambing can be concentrated to a few days saving labor and time in the barn. 2. Transcervical insemination is a method where the cervix is manipulated to allow a small instrument or pipette to pass through the cervix. Semen is then deposited in the uterine body. In recent years, practice and technological advances have allowed the cervix to be penetrated with great success. Conception rates however, have been disappointing for the most part. Reports of vaginal and cervical injury are a serious concern in some cases. This method has not gained wide acceptance due to the variability in conception rates and the cost of equipment. 3. Laparoscopic insemination, the most commonly utilized method today is a minor surgical method where a small amount of semen is placed directly into the uterine horns. In the early 1980s, Australian researches developed a method known as laparoscopic insemination. Now conception rates using frozen semen of 50% to 80% are routine. The number of spermatozoa needed for laparoscopic AI is about one fourth of that required for cervical insemination using frozen/thawed semen. Prior to surgery, the ewe’s estrus cycle is synchronized by the use of hormone therapy. This can be accomplished by the introduction of some type of progestogen product into the ewe, either by use of a vaginal sponge or implant. Over a 12-14 day period, the hormone is slowly released into the ewes body and absorbed by the blood stream. This increased level of progesterone inhibits follicle growth and prevents the ewe from coming into heat. Removal of this implant allows progesterone levels in the blood to fall and follicle development to occur. When the sponge or implant is removed, an injection of follicle stimulating hormone (PMSG or PG600) is given to aid in timely ovulation. Insemination is then performed 52-62 hours (depending on the type of implant used) after the removal of the hormone implant. The insemination procedure takes only a few minutes and the ewe can resume her normal activities shortly after the procedure is finished. The incidence of infection or complications of this minor surgery are extremely low. Successful artificial insemination programs involve many areas of management, including the ewe’s health, successful synchronization, semen handling and quality, the AI technician, STRESS management after AI, and others. All of these areas are linked together like a chain, and the failure of any ONE link will result in lower conception rates. Great success can be realized without a great deal of extra work if attention to detail and good management practices are followed. Economically, AI can greatly benefit a breeding program. Used correctly this management tool can open a completely new avenue for the use of genetic gains not currently available to most breeders. For example, rams, which are no longer alive, or not physically able to breed, can be utilized. Semen from rams can be frozen and stored for use at a future date. Semen from superior domestic and international rams is now available to help improve particular traits. Semen prices range from as little as $15 to as much as $200 depending on the breed and the genetic superiority of the animal. The use of fresh semen is making a come back in today’s AI programs. A ram that is not available for purchase can still be used or a ram in partnership can be utilized by all parties at the same time. Next day delivery and airline travel have made the use of fresh semen not only feasible but an attractive option in increasing conception rates as much as 25% when inseminated laparoscopicly. The use of Artificial Insemination has not found a place in the commercial sheep industry in this country mainly because the economic returns are not realized. Purebred and club lamb breeders however, can benefit from the economic important gains that a successful AI program can add in their program. More research is needed and is currently being conducted on a limited basis to improve the technique and administration of these and other reproductive tools. Results and advancements in this area will benefit all sheep producers in their quest to produce those important economic qualities. Inquiries about this article or any questions pertaining to artificial insemination and semen collection are welcome. For more information, contact Glen Erickson e-mail case570@netscape.net (435) 245-3762
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