The ovarian and hormonal response of the ewe to stimulation by the ram early in the breeding season

The introduction of Dorset rams to Romney ewes at the beginning of the breeding season (February 14 to March 1) stimulated 39% to 70% of the non-cycling ewes to ovulate. Most of the ewes that ovulated did so within 65 to 72 hours of ram introduction. The ovulations were preceded by LH peaks, the mean onset of which was 35.0±4.8 (SE) hours after ram introduction. The mean oestradiol-17β concentration per ewe ranged from 0.3 to 14.9 pg/ml plasma and there were large fluctuations among the samples collected every 3 hours. All ewes, irrespective of treatment, had similar mean concentrations of oestradiol-17β and ovarian follicular activity, and there were no changes in oestradiol-17β concentration that could be attributed to the presence of the rams.