Progestin Treatment of Preovulatory Mares Fails to Delay Ovulation and May Impair Fertility

Controlling ovulation to occur when popular stallions or transported semen is available is desirable to effectively manage broodmares. Some strategies successfully hasten ovulation (e.g., human chorionic gonadotropin and deslorelin), but there is no effective method to delay ovulation in mares. Our hypothesis was that progestins administered during the preovulatory period would delay ovulation without interfering with fertility. The objectives of this study were to determine if: i) CIDR-B or altrenogest can delay ovulation; ii) spontaneous ovulation follows cessation of treatment; iv) treatment affects fertility; v) treatment affects endometrial edema; vi) follicular growth and estrus is suppressed. Fourteen cyclic reproductively sound mares were examined by per rectal palpation and ultrasonography, every one to three d, according to ovarian and uterine findings. [...]