Abstract :
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 (m2 and pe2, 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 (c2) 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.
