Data from 28 performance recorded sheep flocks were evaluated to test for effects of litter size early in a ewe's life, on subsequent litter sizes. Ewes lambing twins at 2, 3 or 4 years of age had litters with on average 0.04 to 0.08 more lambs at each subsequent lambing than ewes lambing singles. The corresponding increases for ewes lambing triplets versus singles ranged from 0.23 to 0.26, with retention of the effect through successive litters. When data were adjusted to accountfor a ewe’s lifetime genetic potential for prolificacy, evidence for an antagonistic environmental effecton litter size following a previous large litter was identified. This effect was approximately twice as high for triplets relative to singles (-0.19 to -0.32) when compared with twins relative to singles (-0.09 to -0.18), and declined in its effect on lambings more than one year later. It suggests that preferential treatment ofewes based on their previouslambing performance might improve their subsequent lambing performance. Culling two tooth ewes based on a single lambing record is unlikely to be economically viable, but there may be situations where reduced flushing of two tooth ewes prior to mating might be justified in prolific commercial flocks. The power and limitations of using data from performance recorded flocks to make recommendations relating to management decisions in commercial flocks is discussed.

PR, Amer, NB Jopson, J Cocks, and AL Scarlet

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 39-43, 2007
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