Genetic Analysis of Raw and Energy-Corrected Test Day Milk Traits in Iranian First lactation Holstein Cows

This research was conducted with the aim of genetically analyzing of raw (RM) and energy-corrected (EC) test day milk in Iranian first lactation Holstein cows. A total of 774,013 test day records belonging to 88,456 first-parity Holsteins (three times milking a day) calving during 1997-2009 in 165 herds (six provinces) was used. Genetic analysis was carried out by a fixed regression test day model in which the effects of herd, calving year, production month, production age, cow genotype (grade or pure Holstein), sperm type, Ali and Schaeffer’s polynomial function, as well as additive genetic and permanent environmental random effects of the cows were included. DMU software was utilized for fitting the model. For the RM trait heritability (0.18) and repeatability (0.535) was higher than that of obtained for the EC trait (0.127 and 0.421, respectively). The results revealed that there was a significant difference (P