Estimation of heritabilities and correlations associated with milk color traits

The objective of this study was to estimate the genetic parameters associat ed with milk color traits of dairy cattle. The data consisted of test day r ecords 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 cr ossbred 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 4 50 nm. From these measurements, fat color and beta-carotene yield were calc ulated. Analyses were performed both within and across breeds. Jerseys produced more beta-carotene than did Friesians, and milk and fat fr om Jerseys had more intense color. Lactation model estimates for the herita bilities 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 heri tability estimates associated with beta-carotene yield were lower than the estimates associated with the color of milk or fat. Genetic correlations be tween beta-carotene yield and the production traits were positive, but gene tic correlations between fat color and production traits were generally neg ative. Genetic correlations between milk color and milk and protein yields were negative, and the correlations with fat yield were close to zero.