Effect of continuous infusion of gonadotrophin-releasing hormone in ewes at different times of the year

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Abstract
Gn-RH (gonadotropin releasing hormone, 3 .mu.g per h for 8 h) evoked a surge of luteinizing hormone in ewes during the anestrous season which was of similar peak height to that found at estrus but of shorter duration. When Gn-RH was given on 3 consecutive days, the response was considerably reduced on the 2nd and 3rd day. Follicles grew as a result of Gn-RH infusion but peripheral plasma estrogen concentration did not increase. During the anestrous season 9/18 ewes ovulated but only 1/6 did so at mid-anestrus. Mature follicles or a CL (corpus luteum) were found in 15/18 ewes that had increased peripheral plasma progesterone concentrations for 1-5 days (11 ewes) or 9-14 days (4 ewes). The concentrations of progesterone found were always lower than those observed during the normal cycle. In the breeding season 10/11 ewes ovulated but there was no evidence that the induced CL were maintained.