Progesterone levels following treatment of seasonally anoestrous ewes with synthetic LH releasing hormone

Abstract

Plasma progesterone determinations were carried out on blood samples collected daily from Clun Forest ewes during the normal oestrous cycle and also after administration of LH releasing hormone (LH RH) during seasonal anoestrus. Levels of plasma progesterone at oestrus ranged from 0.1 to 0.5 ng/ml and luteal phase levels from 3 to 6 ng/ml. Levels found during seasonal anoestrus were within the range of those observed at oestrus. Following treatment with LH RH, there was an increase in the plasma LH level in all cases and ovulation occurred in twenty three out of twenty seven treated ewes. In the animals which ovulated, the plasma progesterone concentration either remained basal (eighteen animals) or rose to a lower level (<2 ng/ml) than that found during the luteal phase of the cycle.