A genetic analysis of 305-day yield in second lactation in Red Danish cattle and Black Pied Danish cattle

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Abstract
SUMMARY The material for the present investigation included approximately 4000 cows in 50 progeny groups from the dual-purpose breeds Red Danish cattle and Black Pied Danish cattle. The main objective was to investigate production in 305 days of second lactation. The characteristics studied were milk yield, butterfat yield and fat content. Analyses of the influence of the four environmental factors, herd average, age at calving, calving interval and calving season, were carried out using least squares. It was shown that age at calving, calving interval and calving season had a curvilinear effect on the yield traits. Herd average yield had a strong linear effect on the yield traits. The reduction in the phenotypic variance due to regression of yield on environmental factors was about 35% for milk and butterfat, and about 18% for fat content. Heritabilities for yield traits in second lactation as well as phenotypic and genetic correlations between the yield traits in first and second lactation were presented. The coefficients of repeatability for milk and butterfat yield diminished from 0·5 to 0·3 when the data were corrected for the environmental factors.