Developing breeding objectives for australian beef cattle production

Abstract

ABSTRACTA sequential procedure for the development of breeding objectives for beef cattle improvement is presented. The procedure is general, and could be used for other types of domestic livestock. The development proceeds in four phases: (1) specification of the breeding, production and marketing system; (2) identification of sources of income and expenses; (3) determination of biological traits influencing income and expense; (4) derivation of the economic value of each trait, based on discounted gene flow methods. As an example, a breeding objective is developed for a pure breeding herd from which male calves are marketed at 9 months of age and surplus heifers are sold at 15 months of age. Situations examined included: (1) the effect of discounting on the breeding objective (income and expense per year v. discounting at 0, 5 and 10%); (2) the effect of ignoring the economic value for food intake in the objective; (3) the effect of inclusion of yearling weight or the deletion of calving date from the selection index. In general, correlations between objectives for discounting and income and expense per year were greater than 0·95, whereas correlations between indices were greater than 0·85. Setting food costs equal to zero shifted emphasis from reproduction to growth traits, with a consequent increase in food intake. The addition of yearling weight to the index caused a small increase in the accuracy of the index, whereas the deletion of calving date had a large effect, halving the accuracy of the index. The practical implications of the results are discussed.