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Genetic Interrelationships of Holstein Milk Composition and Yield¹

Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst

C. J. Wilcox

Department of Dairy Science, University of Florida, Gainesville

B. R. Farthing

Department of Experimental Statistics, Louisiana State University, Baton Rouge

N. R. Thompson

Department of Dairy Science, Virginia Polytechnic Institute, Blacksburg

ABSTRACT

An interregional study of milk composition to determine estimates of genetic parameters was made on 7,943 Holstein records submitted by 19 states. Adjustment for age at freshening was made by cubic regression factors. The reduction in variation due to regression for age for yields ranged to 28% for milk, but was not so marked for percentages except for fat.

Heritability estimates were obtained from variance component analyses of herdmate deviations and lactation records and the regression of daughter lactation records on dam records. Generally, the estimates were in agreement. Heritabilities based on deviations ranged for yields from 0.13 to 0.21 and for percentages from 0.36 to 0.56. Repeatabilities were estimated from deviation and lactation records.

Genetic correlations for deviation and lactation records were in agreement and highly positive among yields and among percentages. Although correlations of milk and percentages were all negative for deviations, they were positive with solids-not-fat and protein percentages for lactations. Selection for milk would be nearly as effective in increasing solids-not-fat, total solids, and protein yields as direct selection. Analyses of lactations suggest selection for solids-not-fat percentage would increase milk production 12% but analyses of deviations indicated this selection would reduce milk production 27%.

¹ Contribution of the Interregional Research Committee on Milk Composition. Research conducted under Southern Regional Project S-49, Genetic Methods of Improving Dairy Cattle for the South, and Northeast Regional Project NE-46, The Genetic and Environmental Factors Affecting the Composition of Milk Produced by Dairy Cattle.