A flock of 224 Dorset x Romney ewes was converted from September lambing in 1977 to 96% autumn lambing (mean 16 May) in 1983 while increasing flock size by 50%. Although various techniques of oestrous induction through teasing were used, it was considered that simply introducing entire rams at least 1 cycle before successful tupping was required, eventually gave good results. Four autumn lambing the interval between joining and the first known conception of mature ewe was 35 d during the early years, and declined to 5 d in 1983 to 1987. This decline is suggested to be a genetic change. After the capacity for out-of-season breeding had been developed in all ewes (1982 to 1987), ewes lambing in spring, when subsequently mated to lamb in autumn after a 7 month lambing interval, showed only an 8% disadvantage in conception over those mated to lamb in the following spring after a 12 month lambing interval. Changes in the flock were brought about by culling of spring-lambing ewes and selection of replacements primarily from early lambers. From 1980, rams born to early lambing ewes were used and their first offspring lambed in 1982. This appears to have had a marked effect on 2-tooth lambing times.
Proceedings of the New Zealand Society of Animal Production, Volume 48, , 61-64, 1988
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