Data from the New Zealand sheep recording scheme (Sheeplan) were analysed to derive estimates of factors affecting weaning weights of lambs from l-year-old dams, and to compare these with estimates from lambs reared by older dams. The linear regression of weaning weight on age at weaning was higher for progeny of yearling ewes than those of older ewes. This probably resulted from later lambing and younger weaning of lambs from yearling ewes. Birth/rearing rank and sex effects were similar for progeny of yearling and older ewes. There was considerable variation between flocks in the size of the effect ascribed to yearling dams. This probably reflects differences in management between yearling dams and older dams in the flocks analysed.
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