Variation in the athletic performance of some mares that appear related to the estrous cycle have been observed. Estrus‐related behavioral or performance problems include difficulties during riding or training, back or flank pain, aggressiveness to other horses or people, frequent urination, colic signs and undesirable estrous behavior during competition or training. Synthetic progestins, including altrenogest (Regu‐Mate), are used to modify undesirable estrus‐related behavior or poor performance in mares. Bilateral ovariectomy (BLO) is regarded by some as a treatment of last resort for mares with estrus‐related problems that fail to respond favorably to pharmacologic treatment. It is widely held that mortality accompanying surgery are reduced when mares are ovariectomized using laparoscopic techniques, and BLO is increasingly popular for treatment of estrus‐related problems in working mares. Therefore, the objective of this research, conducted at Michigan State University, was to compare the perceived improvement in mares with estrus‐related problems administered altrenogest and BLO.

Owners of mares with estrus‐related problem(s) that had undergone BLO after altrenogest treatment completed a telephone survey. They rated the behavioral or performance improvements with altrenogest and after BLO on a 1 to 5 scale (1 = no response; 5 = complete resolution). They also compared improvement with altrenogest and following BLO (1 = better response with altrenogest; 2 = comparable responses; 3 = better response with BLO). Scores for the two treatments were then compared. Twenty mares meet the inclusion criteria for the study. Mares ranged in age from 3 to 15 years with an average age of 9.4 years. Principal estrus‐related problems, identified by owners or trainers, included kicking, bucking or rearing; colic during estrus or ovulation; refusal to work during estrus; aggressiveness to other horses, people or both; stallion‐like behavior; undesirable estrus behavior during work; and flank pain during estrus. Complications related to the BLO procedure were rare. Incisional swelling that resolved without treatment was reported for one mare, and two mares experienced mild colic signs shortly after discharge from the hospital that resolved with treatment of non-steroidal anti‐inflammatory drugs.

Median scores for BLO were significantly higher than those for altrenogest. The association of the perceived response to altrenogest and BLO was positive, but relatively weak. In a substantial proportion of mares with estrus‐related problems, a salutary response to altrenogest was associated with a favorable response to BLO; however, some mares showing limited improvement with the progestagen still responded favorably to BLO. In this series, BLO was perceived by owners or trainers to be at least as effective as altrenogest administration as a means of diminishing a number of estrus‐related behavioral and performance problems. A clearer association of the responses to the two treatments, enabling clinicians to predict improvement after BLO, might be better established with a larger sample size and collection of endocrinologic data to establish the link between undesirable behaviors and hormonal status of affected mares. For more information on this study, click here.

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Estrus And Mare Performance