Using Gibbs sampling to estimate genetic parameters of growth traits in Najdi cattle

The aim of this study was to estimate (co)variance components and genetic parameters for body weights at different ages of Najdi cow using Gibbs sampling of Bayesian approach. For estimating (co)variance components and genetic parameters, the records collected over 21 years (1990-2010) in Najdi cattle breeding station (Shushtar city) was used. The traits were body weights in different age (birth weight, weaning weight, weight at age six months (W6), yearling weight and weight at age 18 months (W18). Environmental factors such as birth year, birth season, sex and age of mother had significant effects on birth and weaning weights (P<0.05). W6, yearling, W18 were significantly influenced by birth year, birth season and sex (P<0.05). The best model obtained for birth weight, weaning weight, and W6 was model 2 in which direct additive genetic effect of animal and maternal permanent environmental effects were taken into account. The best model for yearling and W18 was model 1 in which only direct additive genetic effect of animal was included. Direct heritability for birth weight, weaning weight, W6, yearling weight W18 were 0.45, 0.17, 0.10, 0.18 and 0.13, respectively. Low heritability detected in this study (except the birth weight) is due to high environmental variance. Therefore, the possibility of improving these traits through phenotypic selection is low by and the genetic progress achieved will not be high. In conclusion, good management beside improved environment quality can change the performance of the traits.