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 as oestrus. Following treatment with LH-RH, there was in increase in the plasma LH level in a-l 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 is greater than) than that found during the luteal phase of the cycle.