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Performance of Daughters of High and Average Predicted Difference Sires^1,2,

Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

ABSTRACT

Data on 162 Holstein heifers born over 6 yr and sired by bulls with either high or average Predicted Differences for milk yield were subjected to least squares analysis. Three sets of data (all lactations 419 records, first lactations 162 records, and lifetime records 162 individual cows) involving 16 production traits were analyzed. Breeding to bulls with high Predicted Differences increased milk yield by 670 kg, fat yield by 29 kg, solids-not-fat yield by 58 kg, and protein yield by 23 kg. Genetic trend of sires could not be estimated easily because of a quadratic effect in the regression of production traits on order of sires. The estimate of linear genetic trend for milk yield was positive. The linear regression of lifetime production traits on total days in the herd was positive, and adjustment of lifetime traits to constant number of days in the herd reduced differences between high and average sires.

¹ Journal Paper No. 8487, Purdue University Agricultural Experiment Station, Department of Animal Science.

² Data were derived from the Purdue contributing project to the NC-2 regional project, "Improving Dairy Cattle Through Breeding with Special Emphasis on Selection."