Estimation of heritabilities and correlations associated with milk color traits.

The objective of this study was to estimate the genetic parameters associated with milk color traits of dairy cattle. The data consisted of test day records of 9516 first lactation dairy cows and the records of 6358 of these cows that went on to produce a second lactation. Friesians, Jerseys, and crossbred cows were included in the data. Test day records included measures of milk, fat, and protein as well as milk color measured as absorbance at 450 nm. From these measurements, fat color and beta-carotene yield were calculated. Analyses were performed both within and across breeds. Jerseys produced more beta-carotene than did Friesians, and milk and fat from Jerseys had more intense color. Lactation model estimates for the heritabilities of milk color traits ranged from 0.33 to 0.44 (across breed), 0.40 to 0.49 (Friesians), and 0.17 to 0.31 (Jerseys). In all analyses, the heritability estimates associated with beta-carotene yield were lower than the estimates associated with the color of milk or fat. Genetic correlations between beta-carotene yield and the production traits were positive, but genetic correlations between fat color and production traits were generally negative. Genetic correlations between milk color and milk and protein yields were negative, and the correlations with fat yield were close to zero.