Estimating Genetic Parameters of Body Weight Traits in Kourdi Sheep

For estimating genetic parameters for body weight traits in Kourdi sheep data were collected from 1996 to 2013 in Kourdi Breeding Station in Northern Khorasan province of Iran. Studied traits were birth weight (BW), weaning weight (WW), six-month weight (6MW), nine-month weight (9MW) and yearling weight (YW). The fixed effects in the model were lambing year, sex, type of birth and age of dam. (Co)variance components and corresponding genetic parameters were obtained with the univariate and multivariate analyses fitting animal models using the restricted maximum likelihood (REML) methods. The most appropriate model for each trait was determined based on log likelihood values. Model including maternal genetic effects as well as direct genetic effects, without considering covariance between them, was chosen as the most appropriate model for BW and WW. Model which included only direct genetic effects was the best model for other traits (6MW, 9MW and YW). Year of birth, lamb sex and type of birth were significant sources of variation on body weight traits (P<0.01). Direct heritability estimates of 0.10, 0.28, 0.32, 0.22 and 0.20 were obtained for BW, WW, 6MW, 9MW and YW, respectively. The estimate of maternal heritabilities for BW and WW were 0.27 and 0.13, respectively. Direct genetic correlation estimates between body weight traits were positive ‎and varied from 0.56 for BW-YW to 0.97 for 6MW-9MW. Estimates of maternal genetic correlations between body ‎weight traits were positive and ranged from 0.84 to 0.99. The estimates of correlations between body weight traits suggest that selection for any of these traits could result in genetic progress for the other traits.‎