Phenotypic and Genetic Analysis of Lori‐Bakhtiari Lamb's Weight at Different Ages for Autosomal and Sex‐Linked Genetic Effects

The data set used in this study contained 8793 records of lamb's weight (kg) from 320 sires and 2349 dams collected during 1989 to 2014 from the Lori-Bakhtiari flock at Shooli station in Shahrekord, Iran. Non-genetic factors and genetic parameters (partitioned into autosomal, sex-linked and maternal) of lamb's weight at different ages were estimated using without and with sex-linked genetic effects models. The re-sults showed that the overall mean of lamb’s weight were 5.01, 28.93, 41.42, 51.33 and 56.52 kg at birth, weaning, 6, 9 and 12 months of age, respectively. The effect of fixed factors; year and month of birth, age of dam, sex of lamb, type of birth; dam body weight and age of lamb (days) as linear covariate were signifi-cant (P<0.01 or 0.05) on lamb's weight at different ages. The heritability estimates of lamb's weight ob-tained by most favorable model (without and with sex-linked genetic effects for pre and post-weaning weight, respectively) were low to medium and ranged from 0.08 to 0.22 for autosomal, 0.01 to 0.14 for sex-linked and 0.04 to 0.20 for maternal additive genetic effects. The estimates of autosomal, sex-linked and maternal genetic correlations of lamb's weight at different ages were medium to high. In conclusion, lamb's weight at different ages can be improved by farm management practices and improving environmental fac-tors. Genetic analysis using linear models which able to estimate breeding values in autosomal, sex-linked and maternal separately, could make a more effective genetic selection to improve growth traits in lambs.