برآورد پارامترهاي ژنتيكي صفات رشد و توليد مثل تركيبي در گوسفند نژاد زندي

Genetic Parameter Estimates for Growth and Composite Reproduction Traits in Zandi Sheep Breed

Records of 3257 lambs of Zandi sheep breed, collected from 1991 to 2003 in Khojir rearing and breeding station of Tehran province were used to estimate the genetic parameters for growth traits (birth weight, weaning weight, body weight at 6, 9, and 12 months of ages) along with composite reproduction traits (total weight of lamb weaned per ewe joined through three consecutive parities. Based on univariate analysis, the best model for birth and weaning weights was model 3 (including direct and maternal additive genetic effects). Model 1 (including direct additive genetic effect) was the most appropriate model for body weight at 6,9 and 12 months of ages. According to this model, the direct heritability estimates for growth traits (from birth weight to body weight at 12 months of age) were 0.08±0.04, 0.20±0.05, 0.29±0.06, 0.25±0.06 and 0.35±0.07, respectively. Maternal heritabilities of 0.17±0.02 and 0.06±0.03 weres obtained for birth and weaning weights, respectively. Genetic parameters for composite reproduction traits were estimated using model 1. Heritability estimates of 0.06±0.08, 0.03±0.09, and 0.08±0.11 were obtained from first to third parity, respectively. Covariance components and correlations between growth and composite reproduction traits were estimated on the basis of multivariate analysis, using the most appropriate model in univariate analysis. The highest additive genetic correlation among growth and composite reproduction traits was obtained between weaning weight and TWW2/EJ (0.99). The corresponding estimate for additive genetic correlation among growth traits was 0.99 (between weaning and body weights at 6 months of age). The results of this study indicated that selection on the basis of weaning weight can improve the post weaning and composite reproduction traits.