hCG and Ovulation

Managing a mare’s estrous cycle is an integral part of breeding management, and human chorionic gonadotropin (hCG) is one hormone option for doing just that. Patrick McCue, DVM, PhD, Dipl. ACT, associate professor of equine science at Colorado State University, discussed the use of hCG to manage ovulation.

“Most of us have used hCG throughout our practice lifetimes,” he began. “It’s used to

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Managing a mare's estrous cycle is an integral part of breeding management, and human chorionic gonadotropin (hCG) is one hormone option for doing just that. Patrick McCue, DVM, PhD, Dipl. ACT, associate professor of equine science at Colorado State University, discussed the use of hCG to manage ovulation.

"Most of us have used hCG throughout our practice lifetimes," he began. "It's used to induce a timed ovulation in in-heat mares. We expect that 75-85% of mares will ovulate within 48 hours after hCG administration, and the average interval to ovulation is about 36 hours."

He also briefly discussed the history of another ovulation induction agent–Ovuplant (deslorelin acetate, an analog of gonadotropin-releasing hormone or GnRH). The difference between the two is that hCG mimics the activity of luteinizing hormone (LH), which hastens the maturation and induces ovulation of the dominant follicle in a mare.

In comparison, deslorelin stimulates the pituitary gland to secrete endogenous LH, which will in turn cause follicle maturation and ovulation. Ovuplant was an implant that was designed to be inserted under the skin. When it was first commercially available, it was noted that some mares induced to ovulate with Ovuplant had a delay in their return to estrus. Studies showed that when the implant was removed after ovulation was detected, the incidence of failure to return to estrus was reduced. However, he said that by the end of 2003 the implant was no longer available in the United States. Compounded deslorelin has been used in the equine breeding industry in the past few years, but future availability of the compounded product is uncertain

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Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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