Weighting Sire Evaluations on Different Parities to Estimate Overall Merit

Accuracy of sire evaluations can be increased by a mixed model procedure that analyzes information from the first several parities as information from correlated traits because genetic correlations between yields from different parities are less than one. To increase usefulness of sire evaluations on individual parities, an economic model was developed to obtain factors for weighting information from the first three parities in a sire selection index. Factors in the model were genetic correlations between yields for different parities, conception rate, probabilities of cow survival, matureequivalent yield factors, probability of female calves, age at first calving, calving interval, minimum attractive rate of return, planning horizon, milk price, costs variable with milk yield, and sire evaluations on the first three parities. Genetic correlations, survival rates, minimum attractive rate of return, and planning horizon were varied. Changes of minimum attractive rate of return and planning horizon had greater effect on net present value of a sire's semen than on relative weights of the three parities in the economic index. A rate of return of .1 and a planning horizon of 10 yr resulted in weights of .38 for first-, .21 for second-, and .41 for third-lactation evaluations.