Estimates of Phenotypic and Genetic Parameters for Pre-Weaning Growth Traits of Arabi Lambs

Genetic parameters and (co) variance components were estimated on 2445 lambs from 139 sires and 804 dams for Birth Weight (BW) on 2237 lambs from 127 sires and 784 dams for Weaning Weight (WW) and on 2098 lambs from 115 sires and 739 dams for Average Daily Gain (ADG). The data collected from Animal Science Research Station of Agricultural and Natural Resources Ramin (Khuzestan) University during 2001-2008. Analyses were carried out by Restricted Maximum Likelihood (REML) method. Six different animal models including or ignoring maternal genetic or permanent environmental effects were fitted for traits. The Model 3 with only maternal additive effects seemed most suitable. Influencing factors such as birth year, birth type, lamb's sex and dam's age were investigated as the fixed effects for the models. Estimates of direct heritability from model 3 were 0.194 for birth weight, 0.163 and 0.149 for weaning weight and average daily gain, respectively. Maternal heritability estimates for birth weight, weaning weights and average daily gain were 0.15, 0.11 and 0.09, respectively. For these traits, correlation estimates between direct additive and maternal genetic (r(am)) effects were high and negative ranging from -0.57 to 0.93. Bivariate analysis by Model 3 was also used to estimate genetic correlations between traits. The estimates of genetic, phenotypic and environmental correlations among traits were positive and intermediate to high in value. The results indicate that in addition to additive direct effect, additive maternal effect for all traits was important.