Comparison of Holsteins selected for high and average milk production. 2. Health and reproductive response to selection for milk.

The objective of the experiment was to evaluate direct and correlated responses of secondary (fitness) traits to selection for milk yield. Data consisted of 2768 lactation records from 1078 Holstein cows by 140 sires. Bulls with high PD for milk were mated to daughters of sires with high PD for milk, and bulls with average PD for milk were mated to cows of average genetic merit, creating two genetic lines of cattle. Production, health, and reproductive data were collected. Major health categories were mammary, reproductive, respiratory, digestive, and skin and skeletal disorders. Analyses were per lactation and per lifetime. High PD line cattle averaged 940 kg more milk per lactation than the average line and differed by 500 kg for PTA milk during January 1990. By lactations, the high line cattle averaged 3.8% higher total health costs and 11.2% higher mammary costs than their average herd mates. For most health categories, high line cattle tended to incur higher cost than did average cattle. Selection of sires for high PD milk resulted in daughters that had slightly higher health costs, but total net return was still higher for daughters of high PD bulls.