Genetic Parameter Estimates for Lamb Weight at Post-Weaning in Zandi Sheep, Using Single-Trait Animal Models

The aim of the present study was to estimate variance components and genetic parameters for post-weaning growth traits of 2634 Zandi lambs from 202 sires and 1093 dams for 6 Month Weight (6MW) of 1893 lambs from 188 sires and 816 dams for 9 Month Weight (9MW) and of 1115 lambs from 156 sires and 514 dams for Yearling Weight (YW). Data and pedigree information used in this study were collected from Khojir Research Station (Tehran-Iran) during 1993-2008. Genetic parameters were carried out by Restricted Maximum Likelihood (REML) method, under six different single-trait animal models. Log likelihood ratio test indicated the most appropriate model for 6MW should included direct additive genetic effects as well as maternal permanent environmental effects whilst the most appropriate model for 9MW and YW had only the directed additive genetic effects. The effects of lamb's sex, dam's age and birth year were highly significant on all three traits (p<0.01) but birth type was only significant effect on 6 MW (p<0.05) and was no significant effect on 9MW and YW (p>0.05). Average weights were 27.55 +/- 0.09, 32.67 +/- 0.11 and 34.92 +/- 0.16 kg for 6MW, 9MW and YW, respectively. Estimates of direct heritability (h(2)) were 0.132, 0.134 and 0.133 for 6MW, 9MW and YW, respectively. The estimate of maternal permanent environmental variance as a proportion of phenotypic variance (c(2)) was 0.056 for 6MW.