Mares and Hormones

Estrous cycles and certain disease processes can affect mares’ reproductive hormones.
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Estrous cycles and certain disease processes can affect mares’ reproductive hormones; fortunately, veterinarians have ways to quell resulting behaviors.

Many owners stand by the statement that there’s nothing quite like a hard-trying, intelligent mare. But if you ask for her full attention and cooperation while she’s showing signs of estrus (heat), good luck! Whether they’re causing unsavory behavior in the show arena or preventing a broodmare from coming into estrus, a mare’s hormones can present challenges for owners. With a veterinarian’s help, however, owners can either prevent their mares from cycling or make mares’ estrous cycles more predictable. Let’s first review what estrus is and then explore conditions that can affect a mare’s cycle and how to treat them.

Signs of Estrus

A mare in heat typically exhibits gait abnormalities, raises her tail, urinates repeatedly, and interacts unpredictably with people and other horses. This estrous behavior normally lasts five to seven days, becoming more intense as the ovarian follicles increase in size and produce more estrogen. As the mare ovulates, she goes out of heat and structures on her ovaries begin producing the hormone progesterone (which prepares the uterus for pregnancy). This quiescent period when the mare is not receptive to a stallion is called diestrus, and her behavior can vary from ear pinning and unwillingness to cooperate to kicking, squealing, and striking at other horses. A mare should normally be out of heat for 14 to 15 days; this is the most consistent period in the estrous cycle, so any deviation should alert an owner to have a veterinarian examine the mare.

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Written by:

Jeffrey Cook, DVM, is an ambulatory veterinarian with Rood and Riddle Equine Hospital in Lexington, Ky.

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