Your Guide to Equine Health Care

Double Trouble: Multiple Ovulations in Mares

Researchers recently evaluated multiple ovulations and how vets can detect them and, thus, prevent twin pregnancies.

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Double Trouble: Multiple Ovulations in Mares
The authors concluded that veterinarians should not only examine mares 13 to 16 days post-ovulation to hunt embryos, but also examine the ovaries to see if more than one ovulation occurred. | Amy Katherine Dragoo
They might look cute scampering around a field together, but twins are not desirable in pregnant mares. Multiple ovulations are largely responsible for twin pregnancies, so veterinarians and breeders are often concerned about this phenomenon occurring. Recently, a group of researchers took a closer look at multiple ovulations and how practitioners can detect such ovulations and twin pregnancies early.

“Although rare in many breeds, multiple ovulations, mostly double ovulations, can occur in at least 25% of estrous cycles in Thoroughbreds and Warmbloods,” said Mina Davies Morel, PhD, a senior lecturer in animal reproduction at Aberystwyth University, in Ceredigion, U.K.

Many double ovulations are synchronous (occurring at the same time); however, asynchronous ovulation can occur in which two eggs are ovulated several days apart. Because equine sperm is known for its longevity, it can live inside the mare’s reproductive tract for several days. If a mare is bred at the time of a first ovulation but a second ovulation occurs five or six days later and that egg is also fertilized, two embryos of different ages can coexist.

“In this scenario, if a routine ultrasound examination were conducted 14 to 16 days after the first ovulation, it is possible the second embryo would be missed,” Davies Morel explained. “This is because embryos can’t usually be seen on ultrasound until 11 days after

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Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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