The proportions of ewes ovulating and ovulating multiples were recorded monthly from July-April in Poll Dorset ewes at 2 locations, and in Romney ewes at 4 locations. Flocks of 50-100 ewes were split into two groups and alternated from being isolated to being with vasectomised Dorset rams. Romney ewes differed between locations in ovarian activity even in July (83 and 56% ovulating in Levin and Ohakune). Romney ewes were anovular by September-October. By contrast, Poll Dorset ewes had a similar trend to ewes ovulating. Poll Dorset ewes at both locations returned to full ovarian activity between late December and January. In Romney ewes there were differences between locations in onset of ovarian activity, with the earliest location being Takapau, and Ohakune the latest. Onset of ovarian activity was 2-3 weeks earlier for teased than for isolated Romney ewes. The response to teasing at the end of the breeding season was small (12-15%) compared to the beginning of the season (44%). In a second experiment, 2500 mature Romney ewes were randomly allocated to two groups. One group was joined on 15 April and the other on 10 June. There were no differences in ewes lambing (96 v 97%) but multiple births declined from 44% for the early to 18% for the late joined ewes. This was partially offset by higher lamb survival in the later joined ewes (88 v 79%).
Proceedings of the New Zealand Society of Animal Production, Volume 49, , 229-232, 1989
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