Estimation of (co) variance components and genetic parameters for body weight traits in Zandi sheep using a Bayesian approach

In this study, (co) variance components, genetic and phenotyping parameters for body weight traits at different ages of Zandi sheep breed were estimated. Birth weight, weaning weight, 6-month weight, 9-month weight and yearling weight were studied. The data were collected during 1991-2011 by Nakhjir breeding station in Tehran. (Co) variance components were estimated by Bayesian statistical method based on Gibbs sampling technique. Environmental factors of birth year, sex of lamb, birth type and mother's age were significant on all traits. Appropriate fitted models (based on lowest residual variance) for birth weight, weaning weight, 6-month weight, 9-month weight and yearling weight were found to be models 5, 5, 2, 1 and 1, respectively. Direct heritability was found to be 0.15±0.01, 0.26±0.003, 0.21±0.002, 0.25±0.003 and 0.26±0.001 for the traits, respectively. Maternal heritability of birth weight and weaning weight were 0.11±0.01 and 0.06 ±0.001, respectively. The results revealed that growth traits are more influenced by mother’s genetic factors in the early of age. With increasing the age of lamb and decreasing dependency to the mother, the significance of maternal effect reduced. Low to moderate heritability of the traits indicate that selection for these traits will result in a low to moderate genetic improvement.