Induction of ovulation in anestrus ewes using a dopamine receptor antagonist

Estradiol decreases the pulse frequency of LH during the nonbreeding season through dopaminergic neurons that results in anestrus in the ewe. Long-term administration of sulpiride, a dopamine antagonist, induced ovulation in seasonally anestrus mares. Accordingly, we tested whether sulpiride would induce ovulatory estrus in seasonally anestrus Malpura ewes. A total of 12 Malpura ewes were divided into sulpiride (at 0.6 mg/kg b.i.d.) or control groups. Anestrus was defined on the basis of the absence of heat signs for 2 months through twice-a-day heat detection during the nonbreeding season (October–November) and progesterone level of less than 1 ng/mL. Rates of estrus induction, ovulation, multiple ovulations, and lambing in the sulpiride-treated ewes were 83.3%, 100%, 16.6%, and 66.7%, respectively. The mean interval from treatment to estrus was 5.25 ± 1.49 days. Progesterone levels were elevated after ovulation significantly on Days 5 and 7 after estrus as compared to Day 0 after sulpiride treatment (P < 0.05). In contrast, none of the control group ewes showed either estrus or ovulation. There was a significant association between sulpiride treatment and estrus induction rate as well as ovulation rate (P < 0.05). It is concluded that the result provides proof of concept that the dopamine antagonist can induce ovulation in seasonally anestrus ewes.