Selection Indices for Milk and Fat Yield of Holstein-Friesian Dairy Cattle

Abstract

Estimates of heritability, phenotypic and genetic correlations for milk and fat yield and fat per cent were obtained from the single lactation records of 20,024 daughter-dam pairs of the Holstein-Friesian breed. The estimates of heritability were 0.27, 0.57 and 0.24 for milk yield, fat per cent and fat yield respectively. The phenotypic correlations were 0.89 between milk yield and fat yield, -0.20 between milk yield and fat per cent and 0.25 between fat per cent and fat yield. Corresponding genetic correlations were 0.77, -0.33 and 0.34. The above estimates of parameters were used to construct selection indices for milk and fat yield. Results indicated that a selection index for milk yield alone would be expected to be most effective in improving milk and fat yield of dairy cattle.