Preliminary Evaluation of Treatment With Long-Acting Estradiol Cypionate and Sulpiride for Advancing First Ovulation of Year in Postpartum Acyclic Mares

• Early foaling nonlighted mares are at risk for entering anestrus after parturition.
• Dopamine antagonists have been shown to hasten onset of cyclicity in nonlactating anestrus mares.
• This trial investigated use of dopamine antagonists plus estrogen in postpartum anestrus mares.

Two preliminary trials were performed to evaluate the efficacy of long-acting estradiol cypionate plus sulpiride treatment for hastening the first ovulation in postpartum acyclic mares. In 2010 (year 1) and 2012 (year 2), mares that had foaled in January or February and that were ≥7 ± 1 day postpartum were teased to a stallion to detect estrus and examined by transrectal ultrasonography 3 times weekly. Mares identified as acyclic were alternately assigned to treatments as follows: year 1—group ECP-SUL (n = 5)—same day intramuscular (IM) injection of 50-mg long-acting estradiol cypionate (ECP) plus 1.5-g long-acting sulpiride (SUL), or CON (n = 5)—control; year 2—ECP-SULX2 (n = 4)—IM injection of 100-mg ECP, followed 2 and 7 days later with IM injection of 1.5-g SUL, or CON (n = 5). When a follicle ≥35 mm in diameter, prominent uterine edema and a relaxed cervix were detected, an ovulation-inducing agent was administered. Examinations continued at 2- to 3-day intervals until ovulation was detected. Median (range) interval to ovulation did not differ in year 1 between SUL-ECP (76 days; 31–90 days) and CON mares (74 days; 35–98 days; P = 1.00), or in year 2 between ECP-SULX2 (48 days; 36–66 days) and CON mares (39 days; 39–71 days; P = .91). The injection of the dopamine antagonist sulpiride in a sustained release form in conjunction with the estrogen ECP failed to shorten the interval to the first ovulation of the year in these two groups of postpartum acyclic mares.