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Breeding Programs with Cooled and Frozen - Thawed Stallion Semen

By: Dr. Sylvia Bedford-Guaus

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Insemination Dose

  • The minimum recommended dose to achieve reasonable success for insemination with fresh and cooled equine semen is 500 x 106 (million) progressively motile spermatozoa. But remember: even though it only takes one, the more sperm used to inseminate a mare the better the chances for impregnation.

  • The adequate breeding dose for frozen-thawed semen has not been worked out. Most specialists in the field, however, recommend a minimum of also 500 x 106 progressively motile spermatozoa based on post-thaw motility. This is a controversial topic, and pregnancy rates with frozen-thawed semen are not predictable even when using optimal numbers of progressively motile sperm.

    Insemination Volume

    Some veterinarians and breeders claim that large insemination volumes will cause uterine infections in mares, and may insist on shipping no more than 50-ml of extended semen. Unfortunately, this may compromise the number of viable sperm available to inseminate the mare and thus pregnancy rates may be reduced. There is no research that supports this and, in the case of cooled semen, you should always send as much available extended semen as you can possibly fit in the shipping container.

    For example, a research study in pony mares compared pregnancy rates using 30 and 120-ml of extended semen, when both volumes contained an sufficient number of progressively motile sperm. Pregnancy rates were not statistically different, and where slightly higher in the group inseminated with the 120-ml treatment. One mare developed a significant post-insemination uterine infection, and that was after using 30 ml of extended semen!

    Mares that are susceptible to postbreeding infections may get infected regardless of insemination volume. A typical example is when breeding with frozen-thawed semen. Even though insemination volumes are as small as 0.5 to 5 ml, some mares may still develop significant post-breeding infections due to an inflammatory reaction against the sperm itself.

    Insemination Timing

    Good breeding management of the mare to be bred with cooled or frozen-thawed semen is as important as good management of semen at the stallion's end. The key to good breeding management is timing of insemination in relation to ovulation.

    Any mare in a breeding program should be closely monitored for signs of heat, by teasing, and then her reproductive tract closely followed by palpation and ultrasonography per rectum to ascertain the optimal timing for ordering semen (in the case of cooled semen) and/or insemination.

    The use of reproductive hormones such as Prostaglandin F2a, to "short cycle" or bring the mare into heat, and human chorionic gonadotropin or deslorelin (Ovuplant) to induce ovulation, will facilitate management of mares for breeding with transported or frozen-thawed semen.

    In general terms, cooled semen should be inseminated within 48 hours of ovulation. The closer to ovulation the better, but 24 to 48 hr will do.

    In the case of frozen-thawed semen, optimal pregnancy results are obtained when breeding within 6 hours of ovulation. If the semen quality is excellent, one can stretch it up to 12 hours, but I do not recommend it. Insemination with frozen-thawed equine semen beyond 12 hours before or after ovulation will yield extremely poor pregnancy rates.

    Research has also shown that it is always better to breed before rather than after ovulation.

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