The application of body weight data to performance testing of beef cattle

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Abstract
A least squares method particularly suited to automatic computation, for calculating adjustments to remove extraneous variation in performance test data, is described. Multiplicative adjustments can be calculated for discontinuous variables, e.g. sex, or for continuous variables, e.g. age at weaning. By calculation of all desired adjustments simultaneously each adjustment factor is as free as possible from the effects of the other variables. Results are given of the application of the technique to weaning weights of stud Hereford and Aberdeen Angus cattle reared on one property. With the use of several different models of analysis, the effects of age of dam, sex, year of birth, age at weaning, sire, and birth weight were investigated and comparisons drawn between the two breeds used, and between this study and other published work. The effect of some of these variables on birth weight is discussed, and the relative effects of some of the variables on weaning weight and birth weight compared. The use of a combination of traits to form a selection index is also discussed.