Valuing lamb sires : the effect of estimated breeding values for weight and fat in a declining lamb market.

Three hundred and twenty lambs, sired by Poll Dorset rams with a range of estimated breeding values (EBVs) for weight and fat, out of Border Leicester x Merino dams, were born in March and April and grown through to mid August, mid September or mid October. Lambs were slaughtered if they were over 48 kg live weight or had GR tissue depths over 15 mm with the balance slaughtered in October. Growth rates from weaning to September and the August live weight were related to EBVs for weight with the August weight (mean 36.8 kg) increasing by 0.242 kg/kg EBV. The regressions between EBVs for fat and fat measurements were positive, although not significantly different from zero. A carcass value was estimated based on average NSW lamb prices in August, September and October with discounts for over fatness and feed costs. This value was significantly related to EBV for fat with the highest value carcasses from the lean, fast growth sires. The value increased by $0.07 for each 1% increase in the lean growth index.