Mares behaving badly: a review of methods for estrus suppression in the mare*

Abstract

Mares are seasonally polyestrus and based on the presence or absence of reproductive hormones, specifically estrogen and progesterone, their behavior can vary throughout the year. Concerns pertaining to mare behavior are often attributed to their estrous cycle, however undesirable mare behaviors need to be differentiated from other non-reproductive causes of undesirable behavior. While behaviors consistent with estrus are described as increased frequency of approaching the stallion, leaning hindquarters toward the stallion, relaxed facial muscles, slightly lowered head, ears turned toward the side, posturing, clitoral eversion, and passive urination, common client complaints such as kicking, tail swishing, or poor attitude may be related to the diestrus phase of the estrous cycle. Display of these behaviors alone may not directly relate to the issues with the estrous cycle and, in particular, if not displayed under controlled teasing conditions with a stallion. Multiple treatments have been utilized by veterinarians for estrus suppression and manipulation, however some of them are poorly effective while others may actually promote estrous behavior. Treatments can be categorized as progestogen supplementation, extension of the luteal phase, suppression of ovarian follicular activity, ovariectomy, and non-traditional or alternative therapies. This review details the individual therapies available for the potential treatment of estrous behavior and each therapy’s associated efficacy.