Estrus Suppression

The expression of behavioral estrus can have a profound negative effect on training and performance. Mares may be in estrus approximately 20–30% of the normal 21-day estrous cycle during the physiological breeding season. Numerous techniques to suppress or modify the estrous cycle or estrous behavior of the mare have been reported, including hormone administration, herbal supplements, non-steroidal anti-inflammatory drugs, acupuncture, intrauterine devices, and surgery. Daily oral administration of the synthetic progestin altrenogest at a dose of 0.044 mg/kg is very effective and is considered the “gold standard” for the suppression of estrus in mares. Implants used to promote weight gain and feed efficiency in cattle that contain progesterone and estradiol have been administered to horses in an attempt to suppress heat.