Influence of the Presence of Rams on the Luteinizing Hormone Surge After Oestradiol Benzoate Injection in Ovariectomized Ewes

I.N.R.A., Station de Physiologie de la Reproduction, 37380 Nouzilly, France (Received 13 September 1974) The continuous presence of rams reduces the duration of the sexual receptivity both in intact ewes during spontaneous oestrus (Parsons & Hunter, 1967) and in ovariectomized ewes after progesterone-oestrogen treatment (Fletcher & Lindsay, 1971). Moreover, the exposure of intact ewes to rams accelerates the surge of luteinizing hormone (LH) resulting in earlier ovulation (Lindsay, Cognié, Pelletier & Signoret, 1975). Oestrogens appear to provide the primary stimulus for the LH surge in the ovariectomized ewe (Pelletier & Signoret, 1970; Scaramuzzi, Tillson, Thorneycroft & Caldwell, 1971). This present experiment was designed to investigate a possible 'male effect' on the timing of the pituitary release of LH after progesterone-oestrogen treatment of the ovariectomized ewe. Thirty-seven mature Ile-de-France ewes, ovariectomized at least 1 month before the hormone injections, were used in the experiment. They were primed by five