FSH and LH concentrations preceding post-partum ovulation in the mare

Abstract

Equine follicle stimulating hormone (FSH) and luteinizing hormone (LH) were measured in the serum obtained from pregnant mares, bled daily, from up to 17 days before parturition until the first ovulation after parturition. LH was at baseline levels until 2 days before ovulation when it started, and continued, to rise until after ovulation. FSH surges occurred at approximately 24 and 14 days before this post-partum ovulation (12 and 2 days before parturition), thus showing a similar pattern to the cyclic mare, consistent with the hypothesis that 2 surges at these times prepare and prime follicles for subsequent ovulation. The high plasma oestradiol levels that occurred during and immediately before these FSH surges did not show a negative feedback, or the inverse relationship between FSH and oestradiol which occurs in the cyclic mare, and in other species.