Calculating daughter yield deviations for production traits in Holstein cattle using repeatability animal and random regression test day models

In the present study, the records of milk yield and fat and protein contents collected by the Animal Breeding Center of Iran between 2001 and 2010 were used to estimate the daughter yield deviations of Iranian Holstein bulls. The results were compared with the conventional method of the estimation of breeding values for bulls. The results obtained from a repeatability animal model and random regression test day model were compared. Correlations of bulls' daughter yield deviation with estimated breeding value were 0.65, 0.71 and 0.58 with repeatability animal model and 0.76, 0.92 and 0.91 with random regression test day model for milk yield and fat and protein contents, respectively. Correlation of bulls' daughter yield deviation with estimated breeding value in both models was dependent on the number of daughters and when this factor increased, the correlation of bulls' daughter yield deviation with estimated breeding value increased consistently. Correlation also increased along with increase in the lactation number of daughters and number of test day records for daughters in the repeatability and random regression models, respectively. Correlation between bulls' daughter yield deviation and estimated breeding value in random regression model was greater than that of the repeatability model for all studied traits.