Timing Is Everything
When using frozen-thawed semen for horse breeding, everything has to be synchronized.
By Dr. Dawna Voelkl for AQHA Corporate Partner Zoetis | January 1, 0001
The subject of breeding of mares with frozen-thawed semen often elicits weary-eyed glances from veterinarians, farm managers and mare owners alike. For mare owners, concerns include subjection of mares to frequent transrectal examinations and the associated veterinary expense, while for managers and veterinarians, the principal challenge is managing logistics of repeated examinations. In response to these concerns and challenges, a variety of protocols, yielding similar pregnancy rates, are available. The specific protocol optimizing your mare's probability of becoming pregnant depends upon a variety of factors, including number of doses of semen available, semen quality, whether estrus monitoring and breeding are to occur on-farm or in the clinic, and your individual mare's reproductive history.
The collection, evaluation and freezing of sperm exert tremendous stress upon individual spermatozoa. Thus, sperm longevity following thawing is very short relative to that of freshly ejaculated sperm, six to 12 hours versus 24 to 72 hours, respectively. The fact that the mare's oocyte lives a maximum of 12 hours after ovulation necessitates that the sperm and egg rendezvous is precisely coordinated to optimize the probability for pregnancy. Two basic protocols for breeding of mares with frozen-thawed semen are available to ensure that live sperm are available to fertilize the oocyte when it is available. Both protocols begin with induction of ovulation using either deslorelin or hCG when a follicle of approximately 35 mm and endometrial edema are visualized on ultrasonographic evaluation.
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When only one dose of semen is available, the mare is examined via transrectal ultrasonography beginning 24 hours later and then subsequently every six hours. Upon detection of ovulation, insemination is performed. This protocol is beneficial for mares susceptible to post-breeding inflammation/infection and/or poor uterine clearance. When two or more doses of semen are available, “timed” inseminations may be performed 24 and 40 hours after the administration of the ovulation induction agent. This protocol allows for on-farm breeding and is less intensive and, therefore, less expensive, in terms of veterinary management. Modifications of this second protocol are often applied, including ultrasonographic examinations to ensure that ovulation has occurred prior to the second insemination. When multiple doses of semen are available for breeding of a reproductively healthy mare, the choice of program is based upon a cost-benefit analysis that weighs cost of a second dose of semen against increased veterinary expense for additional examinations if only one dose is used. Dr. Voelkl is an assistant teaching professor of theriogenology (reproduction) at the University of Missouri College of Veterinary Medicine.
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