Estimation of genetic parameters for body weight traits in Baluchi sheep

Genetic parameters for birth weight (BW), weaning weight (WW), 6 months weight (6MW), 9 months weight (9MW) and yearling weight (YW) in Baluchi sheep were estimated using data collected during a 26-year period (1984-2010). Estimates of (co)variance components were obtained by REML procedures by fitting a linear mixed animal model. Significant random effects for each trait were explored by fitting direct additive genetic effects, maternal additive genetic effects, covariance between direct additive and maternal additive genetic effects, maternal permanent environmental effects and common litter effects in different models. The Akaike's information criterion (AIC) test was applied to determine the most appropriate model for each trait. The estimated direct heritabilities for BW, WW, 6MW, 9MW and YW were 0.34, 0.09, 0.06, 0.12 and 0.16, respectively. Corresponding maternal heritability estimates were 0.12, 0.07, 0.05, 0.03 and 0.01, respectively. The variance ratios due to maternal permanent environment (c2) decreased from 0.06 in BW to 0.02 for YW. The variance ratios due to litter component were 0.23, 0.07, 0.08 and 0.12 for BW, WW, 9MW and YW, respectively. Direct genetic correlations between body weight traits were positive and high and ranged from 0.52 for BW-YW to 0.96 for 9MW-YW.