Breeding

Chemical Ejaculation in Horse Breeding

Learn what to do when standard semen collection techniques fail.

A 20-year-old American Quarter Horse stallion was brought into the clinic with a history of penile dysfunction secondary to an acute case of severe colic and profuse hemorrhagic diarrhea. The owner wanted to determine if the horse could still be used as a breeding stallion. The stallion was presented to a mare in estrus, and he displayed excellent libido. However, it was immediately apparent that he had lost erectile function of his penis, as well as sensitivity to both the glans and shaft of the penis. As a consequence, it was determined that semen could not be collected by traditional means using an artificial vagina. The owners elected to pursue chemical ejaculation as a means of obtaining semen from the horse.

Chemical ejaculation (or ex copula ejaculation) is a technique that has been used to obtain semen from stallions when traditional semen collection methods either fail or are not applicable. The technique may be used in a variety of clinical situations, including stallions that cannot physically mount a mare or breeding phantom due to a physical injury, stallions with penile injuries or stallions who have ejaculatory dysfunction.

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A protocol has been developed in which a combination of two medications is used to stimulate emission of semen from stallions. The first medication is imipramine, which has been reported to lower the ejaculation threshold in stallions; the second medication is xylazine, which has been demonstrated to induce passive emission of semen in stallions. The stallion was given an oral dose of imipramine, and one hour later was administered an intravenous dose of xylazine. The stallion ejaculated a small volume of semen, 10 milliliters, at one minute and 30 seconds after xylazine administration. Low volume, high concentration semen samples are common with chemical ejaculation, presumably as a result of the effect of imipramine in reducing accessory sex gland contraction and enhancing ampulla contraction. The next two attempts at chemical ejaculation on this stallion were unsuccessful, so the time between imipramine and xylazine administration was extended to one hour 30 minutes, and the xylazine dose was adjusted slightly. We were again successful again at obtaining semen. A total of 2 billion sperm were obtained, with sperm motility at 60 percent total, 40 percent progressive.

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The owner of the stallion had a mare in estrus the day semen was collected, and the mare was inseminated with a dose of extended semen. A pregnancy examination 14 days later revealed that the mare was pregnant. Subsequently, a total of five ejaculates were collected from 15 attempts for a 33 percent success rate, over a period of 39 days. Sperm from each ejaculate was frozen for use the following breeding season. Six additional mares were bred using frozen-thawed semen, and three became pregnant. In summary, chemical ejaculation is a specialized technique for semen collection that may be applicable to individual stallions with physical, medical or behavioral issues. Check with your American Association of Equine Practitioners-member veterinarian to see if the procedure may help your stallion.