Inhibin as a Possible Indicator of Follicular Development during Perinatal Period in Mares

Plasma concentrations of immunoreactive (ir-) inhibin, FSH, LH, estradiol and progesterone were measured by RIA between -6 and 12 days after parturition in 6 mares. Follicular development was also monitored in the same animals after parturition by ultrasound scanner. Plasma concentrations of ir-inhibin were relatively low before parturition, then rose significantly after parturition, in accordance with the development of 10-30 mm follicles in diameter during the early period of postpartum estrus. In contrast, concentrations of both estradiol and progesterone remained high before parturition, then dropped significantly 1 day after parturition. The present study demonstrated that inhibin is more likely to be secreted from maternal ovaries into maternal circulation than the feto-placental unit during the prenatal period. This suggests that inhibin could be used as a potential indicator of follicular development around parturition in mares.