Abstract

The purposes of this study were to estimate genetic parameters for growth traits and to develop a suitable model for the data set used.  Data were collected in the Zandi sheep breed from 1992 to 2007 from the Khojir Sheep Breeding Station, Tehran, Iran. Number of observation were 5711 for birth weight (BW), 4619 for weaning weight (WW) , 2801 for  body weight at 6-months of age (W6), 2124 for body weight at 9 months of age (W9) and 2113 for yearling weight (W12). (Co) variance components and corresponding genetic parameters were obtained with univariate and multivariate analyses fitting animal models using restricted maximum likelihood (REML) methods that accounted for fixed effects of sex, birth type, age of dam, year of birth and month of birth. Three different animal models were fitted. Based on the most appropriate model fitted, direct heritability, maternal heritability and maternal permanent environmental effect were estimated to range from 0.155 at BW to 0.357 at WW, 0.069 at WW to 0.157 at BW and 0.161 at W9 to 0.171 at W6, respectively. Phenotypic and genetic correlations between all traits were positive, demonstrating the effectiveness of the implemented breeding programs.

Key words: Sheep, body weight, genetic parameters, maternal effects.