Growth rate and efficiency-related traits in Kermani lambs: estimations of (co)variance components and genetic parameters

Using Kermani sheep, the current study estimated (co)variance components and genetic parameters for average daily gain, Kleiber's ratio, growth efficiency, and relative growth rate. Data were analyzed by the average information restricted maximum likelihood (AI-REML) method using six animal models with different combinations of direct and maternal effects. The best-fitting model was determined after testing for improvement in log-likelihood values. The estimates of h(2) for average daily gain (ADG), Klieber's ratio (KR), growth efficiency (GE), and relative growth rate (RGR) in pre- and post-weaning phases were 0.13 +/- 0.6 and 0.17 +/- 0.02, 0.12 +/- 0.04, and 0.16 +/- 0.03; 0.05 +/- 0.05 and 0.07 +/- 0.03 and 0.06 +/- 0.02 and 0.07 +/- 0.01, respectively. Maternal heritabilities (m(2)) ranged from 0.03 +/- 0.01 for relative growth rate in pre-weaning phase to 0.11 +/- 0.04 for average daily gain in post-weaning period. The maternal permanent environmental component (Pe(2)) accounted for 3 to 13% to the phenotypic variance for all the studied traits. Estimated values of additive coefficient of variations (CVA) ranged from 2.79% for relative growth rate at 6 months of age to 23.74% for growth efficiency at yearling age. Genetic and phenotypic correlations among traits were ranged from -0.687 to 0.946 and -0.648 to 0.918, respectively. The result indicated that selection for growth rate and efficiency-related traits would also be less effective in achieving genetic change, because there was little additive genetic variation among Kermani lambs.