The inclusion of multiple expressions of a character over an animal's lifetime into breeding objectives for sheep is considered. Genetic variances at each expression and covariances between expressions are required and the experimental demands to generate suitably precise information are tabled. Experimental evidence suggests that across-age variability exists for weight and quality of wool. Separation of fleece weight of adult ewes (2-6 years) from that of younger animals would seem justified in a breeding objective, since the genetic correlation between the two traits was 0.8 or lower. Fibre diameter, a measure of wool quality, showed evidence of interaction of age with genotype. Fibre diameter stability, or the linear regression of diameter deviation with age, was a heritable trait that accounted for at least some of this genotype X age interaction. Litter size showed no evidence of genetic variability across ages, although the estimates from published data sets could only identify gross departures from unity genetic correlations between age. The implications of expanding a breeding objective for Australian Merino sheep to include lifetime parameters for wool production traits are discussed. The opportunities for considering additional or alternative selection criteria to increase selection accuracy are highlighted.

Kevin D Atkins

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XV. Beef cattle, sheep and pig genetics and breeding, fibre, fur and meat quality., , 17–26, 1990
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