Growth and carcass composition of second-cross lambs. 2. Relationship between estimated breeding values of sires and their progeny performance under fast and slow growth regimes

Abstract

Growth and carcass performance of 2316 ewe and cryptorchid second-cross lambs over 2 years was related to the LAMBPLAN estimated breeding values (EBVs) of their sires. The lambs (56–156 per sire) were sired by 20 Poll Dorset rams from one stud, which were selected to represent a range of EBVs for growth rate and leanness. Half of each lamb sex group was grown at a fast rate from weaning to slaughter at 40 kg liveweight for ewes or 48 kg for cryptorchids. The other half was grown at a slower rate to the same slaughter weights, 10–13 weeks later. Lamb measurements included liveweight approximately every 21 days to slaughter, and fat and muscle depth on live lambs using ultrasound and carcass fat depth. The regressions of lamb weight on sire EBV for weight increased as the lambs aged and were 0.243 ± 0.124 for fasted weight pre-slaughter and 0.158 ± 0.064 for carcass weight. Live lamb C fat depth (45 mm from the mid-line over the 12th rib), carcass C fat depth, and carcass GR (total tissue depth 110 mm from the mid-line of the carcass over the 12th rib) were all related to sire EBV for fat. The regression values for ultrasound C fat depth and carcass GR of 0.156 ± 0.049 and 0.366 ± 0.159 on the sire EBV for fat (mm/mm EBV) were higher than the expected values. The results demonstrate that over a range of sires, 2 years, 2 sexes, and different nutrition regimes there are significant advantages in progeny weight and leanness if sires are selected for high EBVs for weight and leanness.