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Montana State University, Bozeman 59717
Abstract
Records on 5,902 angus and 5,950 Hereford calves born in 15 member herds of the montana Beef Performance Association over a 16-year period were used to calculate additive and multiplicative correction factors for the effects of sex and age of dam on weaning weight. appropriateness of additive versus multiplicative adjustment was evaluated by comparison of the effects of the each on herd x sex, herd x age-of-dam and sex x age-of-dam interactions and on variance within sex and age-of-dam sub-classes. Although there were few clear-cut choices for age of dam, multiplicative factors were preferred for all Angus adjustments be cause of their capacity to reduce interaction effects were generally not as important in hereford analyses and were not affected as much by multiplicative adjustment. additive factors were preferred for age-of-dam Hereford adjustments, and multiplicative factors were preferred for Hereford sex adjustments because the multiplicative factor reduced the difference in subclass variation. an age-of-dam correction to a set of mature ages rather than to a single age was considered adequate and thus preferable because of the smaller number of adjustments required. the presence of interactions, and the failure of adjustment with multiplicative correction factors to make the interactions non significant, suggests that within-herd and sex adjustments should be used where possible.
1 Published with the approval of the Director of the Montana Agr. Exp. Sta., Journal Ser. No. 1097.
2 Present address: Farmers Hybrid, Box 538, Warner, OK 74469
3 The authors express appreciation to the Montana Beef Performance Association, Bozeman, for providing the data for this study
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