Evaluation of models for estimation of genetic parameters and maternal effects for early growth traits of Iranian Baluchi sheep

Genetic and non-genetic parameters were estimated for early growth traits of Iranian Baluchi lambs using univariate and multivariate models. The investigated traits were: birth weight (BWT), weaning weight (WWT), 6-month weight (6MW) and pre-weaning average daily gain (ADG). Data and pedigree information used in this research were collected at the Abbasabad Sheep Breeding Station during a period between 1973 and 2003 on 15,568 lambs descended from 326 sires and 4737 dams. Twelve models including different combination of direct and maternal effects (additive genetic, permanent environmental and common environmental) as well as additive genetic relationship between direct and maternal effects were used to analyze data. For each trait, the most appropriate model was chosen based on likelihood ratio tests. In addition, multivariate analysis was performed using the most appropriate models obtained in univariate analysis. Based on the most appropriate fitted models, estimates of direct heritabilities were 0.12 +/- 0.02, 0.10 +/- 0.02, 0.06 +/- 0.01 and 0.09 +/- 0.02 for BWT, WWT, 6MW and ADG, respectively. Estimates of maternal additive genetic and maternal permanent environmental variances, as a proportion of phenotypic variance (m(2) and pe(2), respectively) were 0.08 +/- 0.02 and 0.08 +/- 0.01 for BWT, 0.04 +/- 0.01 and 0.09 +/- 0.01 for WWT, 0.03 +/- 0.01 and 0.03 +/- 0.01 for 6MW, and, 0.01 +/- 0.01 and 0.08 +/- 0.01 for ADG, respectively. Maternal common environmental component was significant only on BWT and was estimated to be 0.19 +/- 0.02. The estimate of maternal common environmental variances as a proportion of phenotypic variance (c(2)) was significant only for BWT (0.19 +/- 0.02). Direct genetic correlations among studied traits were positive and ranged from 0.37 (BWT-6MW) to 0.98 (WWT-ADG). Maternal genetic correlation estimates between studied traits were positive varying from 0.11 (BWT-ADG) to 0.64 (ADG-6MW). The estimates of phenotypic and environmental correlations were positive and generally lower than those of genetic correlations. Results indicated that besides direct genetic effects, maternal effects should be included in the statistical model to obtain accurate estimates of genetic parameters for early growth traits. (C) 2011 Elsevier B.V. All rights reserved.