Estimation of genetic parameters for milk yield of Iranian Holstein dairy cows using random regression and repeatability models

In the present study، the records collected by Animal Breeding Center of Iran between 2001 and 2010 were used to estimate the genetic parameters of Iranian Holstein milk yield trait with test day and 305 day corrected records. GLM procedure was used for fitting the fixed effects in the statistical models of analysis. Analysis was performed using AIREML algorithm. In random regression model the Legendre polynomial functions of orders (5، 6) were chosen to fit the additive genetic and permanent environmental effects. Heritability and repeatability estimates were 0. 209 and 0. 392 with repeatable animal model and 0. 106 to 0. 278 and 0. 688 to 0. 810 with random regression test day model، respectively. Average heritability of milk yield in random regression model was higher than one in repeatability animal model especially late in the fourth month of lactation، therefore the selection in this period and random regression model can be more accurate.