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International Journal of Dairy Science

Year: 2013 | Volume: 8 | Issue: 1 | Page No.: 30-35
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Authors

A.A. Amin

F.S. Alhur

Keywords

Research Article

Random Regression Animal Model for Genetic Evaluation of Milking Duration in Holstein Friesian Cows

A.A. Amin and F.S. Alhur
The main objective of this study was to apply random regression animal model for analyzing the relationships between repeated measurements of milking duration (MKDr) across different days in milk. The study analyzed data involving 103563 sample test-day records from multiparous Holstein-Friesian cows. A cubic random regression was applied to represent additive genetic variance in all studied traits across all different days in milk (112 groups). Estimates of heritability were very low during the first 60 days of lactation and did not exceed more than 0.04. During the 2nd half of lactation, the estimates ranged from 0.35-0.39. Results of genetic variations for lactation records during early production life showed that an intermediate milking rate could be achieved. Estimates of expected breeding values for milking duration increased in different rates with progressing days in milk groups. Additive genetic correlations between measures at different lactation months continuously decreased with an increase in interval between the test days. Correlations between expected breeding values ranged from 0.41-0.83 (mean = 0.69) across different lactation months. A detailed estimates of breeding values, estimates of permanent environmental and additive genetic correlations for milking duration were tabulated. Overall, application of random regression animal model proved a useful tool for genetic evaluation of milking duration in Holstein Friesian cows.
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