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Artificial Insemination in HorsesBy Kentucky Equine Research Staff · January 19, 2012

Artificial insemination (AI) is an advantageous option for many breeders because it eliminates transporting a horse for breeding and also allows a stallion to impregnate a much larger number of mares than would be possible by live cover. Semen collection and insemination techniques have been refined to make AI an excellent reproductive choice.

Equine semen is collected from a stallion and then used fresh, cooled, or frozen. Fresh semen should be deposited into the mare within a very short time after collection. The semen remains viable in the mare’s reproductive tract for no more than about 48 hours, so every effort is made to ensure the mare ovulates within this period. The mare should be checked to see that she has developed a ripening follicle before insemination, and various drugs can be administered to induce ovulation.

Semen that is not destined for immediate use can be either cooled or frozen. Cooled semen is mixed with an extender before being packaged and transported in an insulated container to wherever the mare is housed. Delivery is usually scheduled for the same or following day. Anticipated ovulation is taken into account when a delivery date is selected. Another consideration is the characteristic of a particular stallion’s semen because some semen retains sperm viability and motility for a longer time than samples from other stallions. Thus, if a mare is predicted to ovulate within 24 hours of collection and the semen comes from a stallion with a poor cooled semen record, shipping should be arranged to guarantee a same-day delivery. If the mare won’t ovulate within this period and the stallion has a good record for cooled semen quality, overnight shipping is a reasonable and less expensive alternative.

Frozen semen that is properly processed and stored retains its qualities for many years. It can be thawed and put into a mare just before or after ovulation, an event that can be verified by ultrasound. As with cooled semen, frozen semen retains its qualities better for some stallions than for others. Owners thinking of using cooled or frozen semen should consider the AI breeding record for a particular stallion as they make their choices.

Insemination as close as possible to the time of ovulation is crucial if pregnancy is to result from any breeding, whether natural or artificial. A mare in heat that has produced a follicle measuring 35 mm or greater is getting close to ovulating, but “close” could mean a few hours or a few days later. Veterinarians have a choice of several drugs that are known to induce ovulation within known time periods, and using AI immediately after ovulation is the best bet for settling the mare.