The effect of weaning weight on subsequent lamb growth rates

The effect of weaning weight on the subsequent growth rate of lambs was estimated from data collected at Winchmore Research Station. The lamb weight data were collected over a 3-year period involving dryland and irrigated farmlets with two contrasting forage systems. Lambs were weighed at 2-weekly intervals with the weights for the periods immediately pre- and post-weaning being used for the comparisons in this study. Results overall indicated that, following adjustments for pasture type, gender, birth and rearing rank, heavier lambs at weaning had faster growth rates post-weaning than lighter lambs. However, lighter lambs suffered a lower drop in growth rate (defined as growth rate before weaning minus growth rate post-weaning) than heavier lambs. This was universal across both pasture types, both genders and all combinations of birth and rearing ranks. Possible explanations are that the lighter lambs at weaning were receiving less milk from their mothers or that they were under some mob pressure and had limited access to quality pastures. In some cases, the lighter lambs even increased their growth rates post-weaning when compared to pre-weaning. It is suggested that weaning light lambs is an option for farmers, particularly when feed supply is limiting or when dry stock are required to clean up poor quality pastures and set up high quality feed for young stock. Keywords: dryland, irrigated, lamb growth, lamb weaning, pasture quality, weaning weights