Advances in Artificial Insemination

Artificial insemination (AI) is becoming an increasingly popular method for breeding horses, and with that comes advances in the timing methods used to inseminate mares. "Breeders have embraced the use of transported cooled semen for all the benefits associated with shipping semen to mares as opposed to shipping valuable mares and foals to stallions for live cover or on-farm AI," said Paul R. Loomis, MS, CEO of Select Breeders Services in Colora, Md., at the Hagyard Bluegrass Equine Symposium held Oct. 21-23, 2004.

"One of the main benefits of using frozen semen is the fact that it can be shipped to the veterinarian or mare owner in advance, thus eliminating the anxiety and logistical headaches associated with cooled semen breeding," said Loomis. However, intense management of mares being inseminated is required in order to ensure the mare is inseminated at the crucial time during ovulation.

"Currently, Select Breeders Services recommends use of a timed insemination protocol for cost-effective management of mares bred with frozen semen," said Loomis. "This protocol involves daily ultrasonographic examinations during estrus, induction of ovulation using hCG or deslorelin (both hormonal ovulatory agents) following detection of a follicle greater than 35 millimeters, and insemination at 24 and 40 hours post-injection. Using this schedule, mares that ovulate 18 to 52 hours after administration of the ovulatory agent will have had sperm deposited in the reproductive tract within 12 hours prior to ovulation or within six hours after ovulation or both."

In a study by Harald Sieme, DVM, of Germany's State Stud of Lower Saxony, mares inseminated twice per cycle at 24 hour intervals had a 50% conception rate, while mares inseminated once averaged a 42% conception rate. Conception rates for mares inseminated once within 12 hours of ovulation were 41%, and when inseminated within 12 hours after ovulation were 50%. Additionally, mares bred once per cycle when the AI was between 12 and 24 hours prior to ovulation, had a 31% conception rate, but when a second AI was performed within 12 hours after ovulation, the conception rate increased to 62%.

"In our Select Breeders Services study of 332 cycles of AI using frozen semen, mares inseminated one time within six hours after ovulation had a 47% conception rate, while mares inseminated twice--once before and once after ovulation--had a 48% conception rate per cycle," said Loomis.

Although this protocol might not be appropriate for all breeding situations, such as with older mares that have decreased fertility, Loomis noted, "This data supports the theory that two inseminations timed to occur both before and after ovulation yield comparable conception rates to a single post-ovulation insemination. A two-dose timed insemination protocol allows a practitioner to examine mares once daily during normal hours without compromising fertility."

About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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