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LAPAROSCOPIC ARTIFICIAL INSEMINATION
A MEANS TO IMPROVE GENETICS

Martin R. Dally
Animal Science Department
University of California - Hopland Field Station

texelFor many years artificial insemination of sheep was thought to be impractical, mainly due to the difficulty of detecting estrus and controlling the ewe's estrus cycle. The inability to freeze ram semen was another factor that limited a wider use of AI. However, today with the use of progestogen and PMSG the synchronization of the ewe's estrus cycle is possible. In addition, ram semen can now readily be frozen which opens the door for interstate as well as international movement of semen. Even with these technological breakthroughs the conception rate of artificially inseminated ewes was relatively low and therefore was not practical for the commercial producer. The main reason for the low conception rate is that semen could only be placed at the opening of the cervix or slightly inside the cervix. The anatomical structure of the ewe's cervix makes the penetration of the cervix nearly impossible. Cervical AI conception rates using fresh or frozen semen are approximately 55% and 25% respectively. If semen could be deposited in the uterus as is the case with cattle, the conception rate would improve to the point where AI of sheep would be practical on a commercial basis.

IMPROVED TECHNIQUE

In 1982, Australian researchers developed a laparoscopic insemination procedure that revolutionized the sheep AI technique. Conception rates using frozen semen range from 50% to 80% when a skilled technician uses a laparoscopic insemination technique to place the semen directly into the ewe's uterus. Laparoscopic AI conducted at the University of California's Hopland Field Station, using frozen semen, has routinely resulted in a 70% or higher conception rate. Individual rams have consistently produced 85% conception rates. Conception rates can vary greatly depending on semen quality, breed of sheep, management, time of year, and the technician's skill. An additional advantage of laparoscopic insemination, also referred to as intrauterine insemination, is that lower numbers of sperm are required per insemination.

SEMEN AND SYNCHRONIZATION

The number of spermatozoa needed for laparoscopic insemination is about one-third of that required for cervical insemination using frozen/thawed semen. A suitable ejaculation is diluted and processed into 50 to 90 1/4cc French straws for laparoscopic insemination. One straw is required per ewe inseminated and contains between 40-60 million spermatozoa post thawing. If frozen pellets are used, approximately 22 pellets can be made per ejaculation, each containing enough semen to laparoscopicly inseminate 3 ewes. Straws and pellets are stored in liquid nitrogen at -196C (-385F). Prior to insemination, the straws are thawed in a waterbath at 37-38C (98.6-100.4F) for 2-3 minutes. Fresh ram semen can be used but insemination should take place within 10 hours of collection.

The laparoscopic insemination procedure is a minor surgical method by which semen is placed in the uterine horns. Prior to surgery, the ewe's estrus cycle should be synchronized by the use of hormone therapy. This normally involved inserting a pessary impregnated with progestogens into the ewe's vagina and leaving it there for 12-14 days. During that period the progestogen is slowly absorbed through the vaginal wall into the ewe's blood stream. The increased level of progesterone inhibits follicle development and prevents the ewe from coming into estrus. Once the pessary is removed, the progesterone level drops off and follicles develop. At the time of pessary removal, PMSG is given to tighten up the degree of synchronization. Normally, 400 international units of PMSG are given. If insemination is to take place at the peak of the natural breeding season and the ewes are in excellent condition the level of PMSG may be reduced to 300 IU. If too much PMSG is administered, the ovulation rate will be too high resulting in an excessive number of multiple births. Insemination should take place 56-66 hours after pessary withdrawal.

PREP AND PROCEDURE

Twenty-four hours before surgery both feed and water should be withheld from the ewes. This reduces the contents of the rumen and bladder. A full rumen and/or bladder may hinder locating the uterus and increase the chance of puncturing these organs during surgery.

The ewe is placed on her back in a laparoscopy cradle and the posterior abdominal region in the area of the pubis is surgically prepared by removing the wool and disinfecting the skin. The ewe is given an injection of local anesthetic approximately 5 inches anterior of the udder and 2 inches on either side of the midline. The cradle is then placed in it's surgical position with the posterior of the ewe lifted to an approximate 40 degree angle. Two very small incisions are made in the skin at the site where the anesthetic was injected to facilitate puncturing the abdominal wall with a trocar. The muscles of the abdominal wall are not cut - the muscle fibers are separated and once the cannula is removed at the completion of the laparoscopy, the fibers return to their normal position in relation to each other. Once the abdominal wall is punctured, the trocars are removed from the cannulas and an endoscope and a manipulating probe are placed through the cannulas into the abdominal cavity.

An endoscope is a special telescope with a fiberoptic light, which permits the technician to view the ewe's reproductive tract. A small amount of carbon dioxide is used in the abdominal cavity to help isolate the uterus from the other organs. The carbon dioxide also has a mild anesthetic effect on the ewe. A manipulating probe is used to bring the uterus into the proper position for insemination. In some cases this is not necessary, as the uterus is already in the proper position. The less the reproductive tract is manipulated, the better the conception rate. Once the uterus is in the correct position, the probe is removed and replace by the inseminating gun containing the semen.

LAI graphic

The technician then punctures the uterine horn half way between the uterine bifurcation and the utero-tubal junction as seen in the graphic. The semen is injected directly into the lumen of the uterus, and the same procedure is repeated on the other uterine horn. The inseminating needle that enters the uterine wall is extremely fine, having an outside diameter of 0.04mm. The insemination procedure takes only 2-5 minutes. Once both horns have been inseminated, the cannulas are removed and a topical antibacterial spray is applied on the two small incisions. In some cases, bleeding may occur which is due to the perforation of surface blood vessels. If excessive bleeding takes place, michel wound clips or staples may be used to close the wound. Experience shows that very little suturing is required. The ewe is removed from the cradle and allowed to walk, under her own power, to a holding pen. Ewes normally start eating within minutes of being place in the holding pen. The incidence of infection because of this minor surgery is extremely low.

ECONOMICS

The genetic gains that AI can offer sheep producers are almost unlimited. Semen from superior domestic and international rams is now available, and straws may be purchased for as little as $15 to as much as $135 depending on the breed and quality of ram. The cost of hormone therapy and insemination will vary based on the number of ewes involved.

Opening Merino FleeceIMPLICATIONS FOR THE SHEEP PRODUCER

AI is the gateway to the use of top sires, both domestic and international. It offers progressive producers the opportunity to make previously unimagined genetic gains in a very short period of time. Rapid genetic gains can be made especially in wool quality and quantity due to their high to moderately high heritability estimates. In selecting a sire one should consider the progeny's ability to adapt to the environment. The possibility of negative effects on economically important traits is particularly important when exotic breeds are being considered.

References

Chemineau P., Y. Cagie, Y. Guerin, P. Orgeur, and J.C. Vallet. 1991. Training Manual on Artificial Insemination in Sheep and Goats. FAO Animal Production and Health Paper 83. Rome.

Evans, G. and W.M.C. Maxwell. 1987. Salamon's Artificial Insemination of Sheep and Goats. Butterworths. Sydney.

*Reprinted from "Wool Production School;" Hopland Field Station Publication 103 

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