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Estimation of Variance Components for Traits Measured on Station-Tested Beef Bulls¹

University of Guelph, Guelph, Ontario N1G 2W1

Abstract

Canadian test station data were used to estimate variance components and heritabilities for average daily gain on test, end-of-test height at hooks, s.c. fat thickness and scrotal circumference for Aberdeen Angus, Charolais, Hereford, Limousin, Shorthorn and Simmental bulls. Preweaning average daily gain records were obtained for tested bulls from the Federal-Provincial Herd Record of Performance program. The sire model for the estimation of variance components for traits measured at central test stations contained contemporary group as a fixed effect, regression on end-of-test age and a random sire effect. The model for preweaning average daily gain contained herd-year as a fixed effect, linear and quadratic regressions on weaning age and a random sire effect. Variance components were estimated separately for each breed using maximum likelihood procedures. Height, fat thickness and scrotal circumference were analyzed with single-trait models, whereas preweaning and test-station average daily gain were analyzed with a two-trait model. Heritabilities, averaged across breeds, were estimated as .25, .44, .85, .49 and .53 for preweaning average daily gain, test-station average daily gain, height, fat thickness and scrotal circumference, respectively. Differences were found between breeds. Average estimates of the phenotypic, genetic and environmental correlations between preweaning and test-station average daily gain were .03, .49 and –.19, respectively.

¹ The authors acknowledge the financial assistance of the Red Meat Program of the Ontario Ministry of Agric. and Food, and of the Natural Sci. and Eng. Res. Council of Canada. G. Crow and M. Donetz are acknowledged for their contribution of the Manitoba data.

² Dept. of Anim. and Poultry Sci.

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