Genetic and environmental parameters of milk protein yields in Holsteins

Milk, fat and protein first lactation records of 27,137 British Columbia Dairy Herd Improvement cows were analysed for gross genetic and environmental influences. The average production was 5,663 kg of milk containing 3.59% fat and 3.23% protein. Age at freshening accounted for 3.0, .3.7, 3.7, .0.28 and 0.15% of the variance in milk, fat, protein, percent fat and percent protein respectively. Cows freshening in the winter had higher average milk, fat and protein yields than those freshening in summer; however, the percentage constituents of both fat and protein were higher for the summer cows than for the winter cows. Heritability of each characteristic and the phenotypic and genetic correlations between different characteristics were derived from paternal half-sib analyses with 100 sire groups. Heritability values were: milk 0.18; fat 0.24; protein 0.21; % fat 0.38, and % protein 0.47. Within herd-year-season phenotypic correlations between milk yield and the percentages were both negative, whereas the correlation between the constituent percentages was positive. Genetic trends in the cow population averaged 51.5 kg, 2.77 kg, 1.87 kg, 0.015% and -0.049% for milk, fat and protein yields and fat and protein percentages respectively. The dollar returns from incorporating milk, fat and protein yields and/or the constituent fractions in various selection indices were estimated for different levels of protein payment. Higher dollar returns will be expected from selection based on total yields than from selection based on either fat or protein percentage. Measuring protein for a genetic program will be feasible only when unrealistically high prices are paid for protein.Land and Food Systems, Faculty ofGraduat