تجزیه و تحلیل ژنتیکی صفات شیر روز آزمون خام و تصحیح شده برای انرژی در گاوهای شکم اول هلشتاین ایران

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<0.0001) between mean breeding value obtained for the RM (0.3159 kg) and EM (0.1818 kg). Different ranking was found for the elite cows evaluated based upon RM and EM. According to the positive and significant genetic annual trend (0.076 kg per year) for the ECM, it is suggested the energy corrected milk should be used t in genetic evaluation of dairy cattle.