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Abstract : |
The objective of this study was to evaluate the relationship between reproductive performance and milk yield in some Iranian Holstein cattle that calved from 2000-2004. Results for current days open for the first lactation indicated a curvilinear relationship with milk yield. These results agree with the accepted management recommendation of a 60 days dry period. Most estimates of heritability of various measures of reproductive efficiency are less than 0.05. The reproductive trait with the highest heritability, 0.096, was previous days dry in the third lactation. Genetic correlations between milk production and reproduction traits were generally positive. Phenotypic correlations were larger than genetic correlations. Genetic correlations among cow fertility in second and third lactations were inclined to be lower than in first lactation, whereas the phenotypic correlations tended to be of the same magnitude and direction in all three lactations. , |
