Genetic and environmental influences on milk and milk component production [Breeding Holstein cows for milk protein content]

Estimates of genetic parameters and environmental correlations were from deviations from modified contemporary average of standardized records of first lactations of Holsteins in Pennsylvania. Records were extended to 305 days and adjusted for month of calving prior to calculation of deviations. Heritabilities from intrasire correlations among paternal sisters were .23, .26, .22, .71, and .64 for yields of milk, fat, and protein, and percentages of fat and protein. Genetic correlations were positive and generally high between yields and between percentages. Correlations of milk yield with percentages were strongly negative. Environmental correlations among paternal sisters in the same herd were .08, .11, .10, -.04, and -.03 for yields of milk, fat, and protein, and percentages of fat and protein. These statistics will be useful to plan optimum selection programs and to improve sire evaluation procedures, particularly for protein content and yield.