Levels of LH, prolactin and oestrogens in the serum of post-partum mares.

The levels of LH, prolactin and oestrogen were measured by radioimmunoassay in serum obtained from six mares during the post-partum period, and LH was also assayed in blood samples collected at 6-hr intervals from four normal cyclic mares during oestrus and at daily intervals during dioestrus. The concentrations of oestrogen and LH suggested that the mares were having ovulatory cycles during the post-partum period irrespective of behavioural oestrus, and the levels of prolactin seemed to rise in association with probable ovulatory LH peaks. In these mares levels of LH had increased significantly (P less than 0-05) by Day 4 of oestrus and reached a peak (140 +/- 48 ng/ml) about 1 day before the end of oestrus. They then declined rapidly and remained at basal levels (10 to 20 ng/ml) during dioestrus.