Genetic Parameters for Somatic Cells, Protein, and Fat in Milk of Holsteins

Lactation records of milk, fat, and protein yields; fat and protein percentages; and two measures of somatic cells were examined and estimates of variance components were obtained. Heritabilities from multiple-trait REML for 1st parity were .16, .16, .13, .38, .48, .05, and .10, respectively, for milk, fat yield, protein yield, fat percentage, protein percentage, SCC, and somatic cell score. In each parity, heritability was lower for protein yield than for fat yield but higher for protein percentage than for fat percentage. Genetically, somatic cells and yields had positive correlations in 1st parity but smaller or negative correlations in 2nd and 3rd and later parities. Phenotypic correlations of somatic cells and yield were negative. For each parity, genetic and phenotypic correlations with somatic cells were higher for protein percentage than for fat percentage.