Abstract
Lactation records (1,017) of Holstein cows, kept in private dairy farm in Egypt, from 2008 to 2015 were used for the study. The objectives were to estimate the effect of some factors on performance and estimate some genetic parameters. Traits studied were 305 day milk yield (305-dMY), lactation period (LP), peak milk yield (PY), number of services per conception (NSC), days open (DO) and calving interval (CI). Data were analyzed using Multi Traits Animal Model. Least squares means were 4436 kg, 215 d and 37 kg for 305-dMY, LP and PY, respectively, and 3.45, 182 d, and 452 d for NSC, DO and CI, respectively. Season and year of calving and parity had significant effects on all traits, except that of year of calving on PY and parity on NSC. Sire had significant effect only on 305- dMY and PY. Estimates of heritability for 305-dMY, LP, PY, NSC, DO and CI were 0.20, 0.07, 0.19, 0.07, 0.03 and 0.07, respectively. Phenotypic correlations among productive or reproductive traits were positive and between productive and reproductive traits were likewise positive. Genetic correlations among productive or reproductive traits ranged from 0.75 to 0.80 and 0.22 to 0.45, respectively.
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