Changes in gonadotrophins and prolactin levels in isolated (seasonally or lactationally) anovular ewes associated with ovulation caused by the introduction of rams

The response of seasonally or lactationally anovular ewes to ram stimulation (teasing) was investigated in Ile-de-France (IF) and Prealpes (PA) ewes. In the first experiment (seasonally anovular IF and PA ewes) the possible role of prolactin (PRL) in the response to teasing was investigated by selective blockage of the secretion of PRL by CB 154 for 7 days before teasing. In the second experiment (lactationally anovular PA ewes) the role of PRL in the teasing response was investigated by studying ewes suckling one or two lambs, which presented differences in LH and PRL concentrations (p<0.025). In the first experiment, before teasing, basal concentration of LH and frequency of pulses were higher in PA than in IF ewes (p<0.001). The concentration of PRL was higher in IF ewes (p<0.001). Treatment by CB 154 did not affect the secretion of LH or FSH in either breed. Following the introduction of rams a rapid increase (<60 min) in concentration of LH, but not FSH, was observed, irrespective of breed or CB 154 treatment. In suckling ewes (Exp. 2) the frequency of pulses of LH was higher in ewes rearing one lamb than in ewes rearing twins (p=0.05). Stimulation by the rams resulted in a rapid increase (<40 min) in the pulsatile release of LH, irrespective of PRL concentration before teasing. In both experiments most ewes ovulated within 3 days of the start of the ram stimulation. It is concluded that PRL concentration does not affect the sensitivity of the brain to stimuli provided by rams. Analysis of hormonal patterns indicate also that hormonal events preceding ovulation are different from those observed in cyclic females.