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Components of Variance of Milk and Fat Yields in Dairy Goats

Department of Animal Science, Cornell University, Ithaca, NY 14853

ABSTRACT

Age-season adjusted records from five breeds of dairy goats on Dairy Herd Improvement test from 1965 to 1976 were used to estimate components of variance for milk yield, fat yield, and fat percentage. The data were 6,452 Alpine, 1,730 LaMancha, 6,897 Nubian, 2,759 Saanen, and 4,007 Toggenberg lactation records. Components of variance were estimated by Henderson's Method 1 with a four-way model that included random effects of herd, year-season, sire, and doe. Herd effects accounted for 22 to 31% of the total variation in milk and fat yields and 15 to 25% of the variation in fat percentage. These effects were large enough to indicate that they must be considered in genetic evaluations of milk and fat production. Sire components of variance were 8 to 10% of the total variation in milk yield, fat yield, and fat percentage. Does accounted for 16 to 25% of total variation in milk yield, fat yield, and fat percentage. Repeatabilities of milk yield, fat yield, and fat percentage varied from .39 to .55 whereas heritabil-ities also widiin herd-year-season ranged from .48 to .62. Heritabilities larger than repeatabilities indicate that confounding may have inflated sire effects. Phenotypic and genetic correlations between milk and fat yields averaged .94 and .86. Milk yield and fat percentage were correlated negatively both phenotypically and genetically, whereas genetic correlations between fat yield and fat percentage averaged .18.

¹ Animal Improvement Programs Laboratory, USDA, BARC Beltsville, MD 20705