Heritability, Genetic and Phenotypic Correlations of Certain Constituents of Cow's Milk

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Abstract
Two-day composite samples of milk were collected from 76 daughter-dam pairs of Holstein and 70 daughter-dam pairs of Jersey cattle. The samples were analyzed for per cent butterfat (BF) by the Babcock method and per cent total solids (TS) by the Mojonnier method, the difference between the two tests being the solids-not-fat (SNF) fraction. The Holstein herd averaged 3.34% BF, 8.58% SNF, and 11.93% TS. The averages for the Jersey herd were 5.45%, 9.54% and 14.99% respectively. The Holstein herd had heritabilities of 0.36% BF, 0.36% SNF and 0.37% TS, the corresponding heritabilities for the Jersey herd were 0.28, 0.34, and 0.34. The very high genetic correlations between milk production and the production of the constituents of milk, as well as between the various constituents themselves, give strong evidence that there are single genes affecting all of these characteristics.