Genetic parameter estimates of pre-weaning growth traits in Kermani sheep

Genetic and phenotypic parameters were estimated on 2332 lambs from 61 sires and 815 dams for birth weight (BW), and on 2182 lambs from 54 sires and 760 dams for average daily gain (ADG), weaning weight (WW) and Kleiber ratio (KR). The data was collected from 1993 to 2004 at Breeding Station of Kermani sheep. (Co) variance components and corresponding genetic parameters were obtained with univariate and multivariate analyses fitting animal models using restricted maximum likelihood (REML) methods. The most suitable model for each trait was determined based on log likelihood ratio tests. Lamb gender, type of birth, age of dam and year of birth were significant sources of variation on BW, ADG, WW and KR (P < 0.01). Direct estimates of heritability for BW, ADG, WW and KR were 0.04, 0.15, 0.27 and 0.08, respectively. The estimate of maternal heritability for BW was 0.24. The estimates of maternal permanent environmental variance as a proportion of phenotypic variance were 0.13 and 0.13 for ADG and WW, respectively. The estimates of the direct genetic correlation between BW-ADG, BW-WW, BW-KR, ADG-WW, ADG-KR and WW-KR were 0.71, 0.68, 0.59, 0.86, 0.76 and 0.89, respectively. The common environmental correlations estimate between ADG-WW was 0.46 and genetic correlation between maternal effects of BW with direct effects of ADG, WW and KR were low and ranged from 0.02 to 0.03. The estimates of the phenotypic and environmental correlation between traits were positive and ranged from 0.21 to 0.94 and 0.02 to 0.95, respectively.