Artificial insemination (AI) is a relatively common practice for the equine breeding industry. Advances over the last few decades have made AI an effective technique with acceptable conception and pregnancy rates. In many cases, utilizing AI over pasture breeding or hand mating results in higher pregnancy rates especially when managing sub-fertile stallions or problem mares.
There are many advantages to utilizing AI over natural mating including eliminating travel distance, disease control and reduction of accidental injury to the stallion or mare. Semen is collected from stallions using an artificial vagina, cooled to extend the lifespan of sperm and then shipped to the location of a mare awaiting insemination. Shipping cooled semen alleviates the need of transporting mares to stallions. Instead, mares can be monitored for estrus, or heat, and semen can be ordered and scheduled to arrive before the mare ovulates an oocyte, or egg. Semen usually arrives in less that 24h by air or 48h if shipped by ground. Upon arrival, a veterinarian or trained technician can inseminate the mare prior to ovulation.
There are a handful of considerations when deciding if AI is the right choice for your program. Timing is critical for successful conception and mares must be monitored when they come into heat for follicular development. Follicles on an ovary contain a single oocyte, or egg, and typically grow 3-5 mm per day but can vary depending on horse breed. Mares should be monitored by rectal ultrasonography on a minimum of an every other day basis beginning on day 2-3 of heat to determine the presence of a single, pre-ovulatory follicle with normal characteristics accompanied by a healthy uterus and cervix. Semen must be ordered and arrive prior to the follicle reaching 35mm in diameter or before ovulation. Semen should be inseminated before ovulation as oocytes begin to lose viability around 4 hours after ovulation. Mares are often given an intravenous injection of human chorionic gonadotropin (hCG) or an intramuscular injection of deslorelin acetate once a follicle has reached 35mm in diameter to induce ovulation 36-42h later, respectively. Once a mare has been given an ovulatory agent, she is on a timed schedule and a delay in semen arrival could mean that she has already ovulated and the opportunity to breed her on that cycle has been missed. To avoid this risk, hCG or deslorelin can be administered after confirmation of semen shipment or upon arrival. Facilities to accomplish these tasks can be relatively simple but a skilled technician or veterinarian is essential for success.
Stallion owners may also benefit from collecting semen for artificial insemination. In general, a single ejaculate from a stallion contains enough sperm to successfully inseminate many mares. Semen can be collected from a stallion, aliquoted into doses and shipped to multiple locations for multiple inseminations. Increasing the number of mares that a stallion can breed from a single ejaculate allows stallion owners to maximize their foal crop and revenue. For facilities not yet equipped for AI, stallions should have approximately 20 mares booked for the breeding season to justify the start–up costs.
Stallions can be trained for semen collection with the use of a phantom or mounting dummy that can be purchased or homemade. Owners will need to invest in an artificial vagina (AV) and a number of essential supplies. Facilities should include access to hot water and a simple microscope for evaluation of sperm motility accompanied by a device for counting the concentration, or number of sperm, in the ejaculate. Shipping semen by air requires certification of the facility as well as shipping containers designed to maintain sperm at 4-5°C for a period of 24-48hr.
Collecting and evaluating semen before insemination allows one to estimate motility prior to insemination, calculate the number of progressively motile or forward swimming sperm and reduce venereal disease with antibiotics present in extender. Whether inseminating fresh or cooled semen, the number of progressively motile cells can be adjusted per insemination dose so that 500 million or 1 billion progressively motile sperm are inseminated into a mare, respectively. Inseminating a mare with an inadequate number of sufficiently motile sperm can increase the number of attempts needed to achieve successful pregnancy.
Freezing stallion semen for AI allows for indefinite preservation of sperm and valuable genetics. Frozen semen results in reduced fertility compared to using cooled or fresh sperm but conceptions rates vary depending on the stallion. Some stallions have sperm that freeze better than others for reasons that are not fully understood. Using frozen stallion semen requires more intense timing and management of the mare as well as a veterinarian or technician that is familiar with deep horn insemination. Sperm are packaged in straws and held in liquid nitrogen and stored until thawing for insemination. Every breed registration in North America allows for the registration of foals produced by AI except the Jockey Club. General costs associated with AI include stud fees, shipping, veterinary exams and hormone therapy. A decision to utilize this assisted reproductive technique should consider all facets and be discussed with a credible veterinarian or technician.
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