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Adjusting Weaning Weights of Simmental Beef Calves to an Age-Constant Basis¹

Cornell University², Ithaca, NY 14853

Abstract

Weaning weights on 382,188 calves collected by the American Simmental Association during 1969 to 1983 were used to evaluate the effectiveness of the standard age-of-calf adjustment method for calves weaned between 160 and 250 d of age. The model included fixed effects for contemporary group, age of dam by sex and percent Simmental of calf and linear and quadratic regressions for age of calf (within age of dam by sex and percent Simmental). Separate analyses were conducted using actual weaning weights and standard 205-d weights as observations. The latter analysis indicated that the standard adjustment procedure did not eliminate the effect of age of calf. There was a consistent negative relationship between age of calf and standard 205-d weight. This relationship was more pronounced in calves from older dams. At extreme ages (160 or 250 d), bias in standard 205-d weights ranged from less than 1 kg to more than 16 kg. A second data set consisting of 96,040 records was used to compare two alternative adjustment methods to the standard 205-d adjustment. Regression coefficients estimated in analyses of the first data set were used. The two alternative methods were to adjust 1) actual weaning weights or 2) standard 205-d weights. The latter method was consistently better when compared across all percentage Simmental categories.

¹ This research was supported by a grant from the American Simmental Assoc., Bozeman, MT.

² Dept. of Anim. Sci.

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