Phenotypic and genetic parameters were estimated for five persistency criteria of milk yield. The criteria included the maximum production of all test-day records per lactation divided by the related mean, standard deviation of all test-day records of complete lactation, the percentage of daily milk retained from the peak to the end of lactation, the ratio of latest testday yield record divided by the mean of all test-day yield records and a criterion that was proposed by Wood (1967), which derived from estimated lactation curve factors in incomplete gamma function. Data set comprised 36487 first lactation yields of Holstein dairy cattle of Iran with at least eight recorded test-days per lactation. Heritabilities based on the univariate models were 0.32 for 305-days milk yield and were between 0.0819 to 0.0469 for persistency criteria. Heritabilities based on the multivariate models were changed a little in comparison to univariate models. Genetic correlation between persistency criteria and 305-day milk yield were between 0.6617 to -0.6124. Genetic correlation between persistency criteria were between 0.9988 to -0.9265. Phenotypic correlation had similar trend to genetic correlation. The result showed that genetic correlation between milk yield and some persistency criteria were favorable for selection and breeding programs
کلید واژگان :Persistency; Milk yield; Dairy cattle; Lactation curve
ارزش ریالی : 600000 ریال
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