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Basics for breeding mares with cooled or frozen semen (Proceedings)

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Aug 01, 2010

Advanced reproductive technologies such as cooled semen, frozen semen, embryo transfer and gamete inter fallopian tube transfer (GIFT) have given horse owners choices and freedom. Mares can be bred at home with semen collected from stallions that live anywhere in North America, Europe or Australasia. Stallions can compete during the breeding season while mares are bred with their previously frozen semen. Embryos can be collected from performance mares between competitions. The genetics of valuable infertile mares can be maintained through GIFT, a procedure that involves the aspiration of eggs from follicles on the donor mare's ovaries. The eggs are then placed in a fertile recipient mare's oviduct after which she is inseminated with semen. But as with all choices, these technologies come with a price. To be successful, a higher level of veterinary expertise is needed, mares need to be examined more often, pregnancy rates are lower and costs are higher. Equine semen does not tolerate cooling, freezing and the manipulation needed for processing as well as other species. So, more money will be spent to obtain somewhat lower pregnancy rates then that seen with natural breeding or breeding with fresh semen by artificial insemination. So before you sign a breeding contract for the stallion of your dreams, read the following so that you do not naively enter into the breeding game.

The ins and outs of breeding mares with cooled semen

To breed mares successfully with cooled semen all parties involved, mare owner, stallion manager and veterinarians, need to cooperate when coordinating the semen shipments with the timing of the mare's ovulation. Before shipping semen, the owner should clarify several points with the stallion manager.

     • The cost of stallion collection
     • The cost of preparing the semen for shipment, the number of collections provided gratis (if any), the cost of shipping semen tanks by air, and when and how the semen tanks must be returned.
     • The days of the week the stallion is collected
     • Times during the breeding season when the stallion will not be available
     • The number of days notice that the stallion manager needs before the semen shipment
     • The latest time one can call to obtain semen (for example-one must call by 9am to receive semen by the next day)
     • The longevity of the semen-does it live in the tank for 12, 24 or 36 hours
     • First-cycle conception rate of the stallion
     • The method of air transport used (same-day air or overnight shipment.
     • Number of times the mare can be bred if she does not conceive (is the contract limited to 1, 2 or 3 years)
     • The breed registry requirements, and the number and timing of post-insemination clinical (pregnancy) examinations must be established.

Management of mares for breeding has changed in the last 15 years as more mares are bred on farms where there are no means for teasing the mare to determine where she is in her estrous cycle. Stabling a mare at a veterinary clinic or farm where the veterinarian visits daily, saves money on veterinary travel fees. Furthermore, many of these facilities have a stallion to tease the mare to determine when she is in heat, thereby, limiting the number of examinations. Once the mare is in heat, she will need to be examined at least every other day and bred within 24 hours of ovulation.

Pregnancy rates are highest when mares are bred within the 24 hours that precede ovulation using semen of high fertility. The quality of the semen is of paramount importance: stallions with low fertility usually have much lower first cycle pregnancy rates than those with high inherent fertility. In addition, the handling of the semen is critical; failure to prepare it correctly as well as poor subsequent handling at the mare end can make the process very disappointing. Timing of the breeding with the ovulation can be difficult especially if the stallion is collected only 3 times a week. Ovulation can be induced with drugs such as hCG or deslorelin, however the window from injection of the drug to ovulation varies. Mares may ovulate as quickly as 24 hours, as late as 48 hours after administration of hCG or they may not respond at all. The window from injection of deslorelin to ovulation is tighter than that of hCG with most mares ovulating between 42 and 48 hours, however, it costs about 2.5 times more than hCG.

There are standards that semen needs to meet to be considered of adequate quality. There is controversy on what is an adequate semen dose for shipment. The old rule of thumb was a dose of semen should contain a minimum of 500 million progressively motile sperm with at least 30% of the sperm being progressively motile. However, some stallions have acceptable pregnancy rates with doses of 250 million progressively motile sperm. Many farms are now shipping a dose of 250 million sperm/bag. The minimum dose will vary between stallions so it is prudent to contact stallion managers if one is experiencing low first cycle pregnancy rates in reproductively normal mares. Each time the mare is bred with cooled semen, it should be examined carefully after it has been warmed for a minimum of 3 minutes. If it is of poor quality the stallion manager or veterinarian for the stallion should be notified. In a study from Texas A and M, reproductive records from all mares bred with cooled semen were reviewed. The group showed that first cycle pregnancy rates were approximately 65% if the mare was bred with a minimum of 500 progressively motile sperm. However, first cycle pregnancy rates dropped to less than 30% if mares were bred with a lower number of motile sperm. We recommend that the stallion manager place at least 1 billion progressively motile sperm in the package before shipment so that 24 hours later when the mare owner receives the semen, there is at least 500 million progressively motile sperm in the dose.

After insemination, the reproductive tract of the mare should be examined daily until she ovulates. If she does not ovulate within 24 hours she should be bred a second time. Age of the mare may affect her ability to get pregnant. Mares that are more than 10 to 12 years old when they are bred for the first time may retain fluid in the uterus after breeding because their cervix does not open properly. When semen is deposited in the uterus, the mare responds with an inflammatory response because the semen is recognized as a foreign substance. Reproductively normal mares clear the fluids that are associated with the inflammation within 12 to 18 hours of mating, those that do not, accumulate fluid. The inflammatory products in the fluid are harmful to the uterine lining as they have a low pH (acid). Your veterinarian can identify if your mare has a cervical problem before she is bred or at the time of breeding. Mares that have an incompetent cervix should have their uterus lavaged with saline or lactated ringers 4 to 8 hours after breeding to remove the fluid before it causes significant damage to the uterine lining.