Many mare owners seek to eliminate estrus behavior when they do not want to breed their mare or when there is a perceived negative effect of estrus behavior on the mare’s performance. The "Estrus Suppression in the Mare" table topic session at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn., began with a discussion of reasons for estrus suppression and approaches practitioners use to guide their clients through selecting a method of estrus suppression. The veterinarians in attendance listed available methods for estrus suppression and discussed preference, efficacy, and problems associated with the treatment.

Many practitioners administer exogenous progesterone/progestin with reported good results. Altrenogest is the most commonly used drug. Practitioners most frequently use the oral formulation, although some have used a compounded slow-release intramuscular formulation. Other progestins owners and veterinarians often discuss are not always efficacious. Progesterone/progestin treatment is usually started just after ovulation. This treatment stops estrus behavior signs but does not eliminate follicular development.

For several years veterinarians have used intrauterine marbles to suppress estrus, but this method is slowly falling out favor because of poor efficacy and increasing reported incidence of complications such pain, uterine infection, and uterine irritation if the marbles break. In addition, removal of the marbles is often difficult.

Another approach practitioners are using increasingly is injecting oxytocin (60 IU) daily from Day 7 to Day 14 after an ovulation to prolong