Breeding season of Romney and Poll Dorset ewes at different
locations and the reproductive penalties of a June joining
T.W. Knight, S.G. Kannegieter, G.J. Hamilton
Batchelar Agricultural Centre, PO Box 1654, Palmerston North
Proceedings of the New Zealand Society of Animal Production.
1989, 49: 265-270
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%).
Keywords: NZSAPAB;
Romney; Poll Dorset; ovulations; breeding season; lambing;
teaser ram effect
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Last Updated 18-03-1997
