Genetic Evaluation of Test Day Milk Records of Holstein Cows in the Northern Provinces of Iran Using Random Regression Models

This research used the test day data of the milk production of Holstein cows from Golestan, Mazandaran and Guilan provinces collected by Animal Breeding Center of Iran between the years of 1988-2011. Permanent effects of model, including cattle blend, breeding year and season, also percent of Holstein gene and age during recording, were used as a secondary variable. All data obtained in this research was 92943 test day records of milk production from 12855 Holstein heifers. DFREML was applied to estimate variance components and genetic parameters in test day models (with random regression restricted maximum likelihood method). A third-order Legendre polynomial has been used in order to considering genetic and permanent environmental variations of milk production for cows lactation period. Analyzing the environmental factors made by SAS software program. Maximum estimation of genetic, phenotypic and permanent environmental correlations of milk yield was 0.99, 0.61 and 0.98, respectively The results of this research shows that the heritability of milk production are different from each other in the different months of lactation period and was achieved in the range of 0.08- 0.19, respectively.