GENETIC-PARAMETERS FOR LIVEWEIGHT AND ULTRASONIC FAT DEPTH IN AUSTRALIAN MEAT AND DUAL-PURPOSE SHEEP BREEDS

The genetic and phenotypic variances and covariances for liveweight at 5 to 19 months of age and ultrasonic subcutaneous fat depth were estimated using REML procedures for the Border Leicester, Suffolk, Corriedale, Coopworth and Gromark breeds. The data comprised 12923 progeny from 46 flocks, representing 590 sires, and were collected by the New South Wales Meatsheep Testing Service between 1981 and 1990. Fixed effects included in the model were management group, birth type, rearing type, age of dam and age of lamb. Each breed was analysed separately, and the larger breed data sets (Border Leicester and Suffolk) were split on age at measurement. The estimates of heritability for the various data sets ranged from 0.09 +/- 0.09 to 0.40 +/- 0.10 for liveweight and 0.07 +/- 0.08 to 0.40 +/- 0.07 for fat depth. There was a moderate positive genetic correlation (0.14 to 0.77) between liveweight and fat depth. Adjustment of fat depth for liveweight reduced this genetic correlation (-0.34 to 0.24) and had little effect on the heritability of fat depth, which then ranged from 0.06 +/- 0.08 to 0.44 +/- 0.07. Variation in estimates between the breeds is discussed. The results will be used to provide breed-specific parameters to improve the accuracy of Estimated Breeding Values produced by LAMBPLAN, Australia's national performance testing scheme for meatsheep. The mean age of sires at the birth of progeny varied from 3.2 to 3.5 years amongst the breeds, with 14% to 30% of animals sired by rams 5 years of age or older. Sire-use patterns in some breeds indicated high levels of inbreeding.