Model comparisons and genetic and environmental parameter estimates of growth and the Kleiber ratio in Horro sheep

Genetic and environmental parameters were estimated for pre- and post-weaning average daily gain (ADG1, ADG2) and Kleiber ratio (KR1, KR2) using the ASREML program. Twelve models, formed with inclusion or exclusion of the maternal genetic, permanent environmental and common (litter) environmental variance components and the covariance between the direct and maternal additive effect on the basic direct additive genetic model, were used. The same models were applied to birth weight (BWT), weaning weight (WWT) and bi-monthly weights to 12 months of age (WT2 to WT12), and weight at 18 months of age (WT18). Two-trait analyses were done among all traits. Maternal genetic and common environmental components were found to be important for ADG1, KR1 and weights up to six-months of age, while the common environmental component was found to be important for ADG2 and KR2. The maternal permanent environmental component was important for WT2 and WWT. Total heritability estimates for ADG1, ADG2, KR1 and KR2 were 0.13, 0.04, 0.13, and 0.01, respectively. Direct genetic correlations of ADG1 with BWT, WWT and WT6 were 0.01, 0.96 and 0.84 while with KR1 they were -0.40, 0.75 and 0.66, respectively. The relatively higher heritability in weight traits and the presence of positive and high correlations of weight traits with daily gain and Kleiber ratio tend to suggest that it would be more practical to select on the weight traits to improve gain and efficiency.