Genetic analysis of Lori Bakhtiari lamb survival rate up to yearling age for autosomal and sex linked
Abstract The data set used in this study contained 8793 records of lamb survival rate from 320 sires and 2349 dams collected during 1989 2014, from the Lori Bakhtiari flock at Shooli station in Shahrekord province, Iran. The data were analyzed using a linear mixed model including fixed factors such as year and month of birth, sex of lamb, birth rank, age of dam, lambs birth weight as quadratic covariate and dam body weight as linear covariate and direct additive genetic (partitioned into autosomal and sex linked) maternal additive genetic and residual random effects. Genetic parameters and breeding values of cumulative lamb survival rate from birth up to yearling age (at 1, 2, 3, 6, 9 and 12 months) were estimated using restricted maximum likelihood procedure. The results showed that the overall mean of the cumulative survival rate of lamb up to yearling (12 months of age) was 80.85% The effect of fixed factors; year and month of birth, sex of lamb and lamb birth weight as quadratic were significant p p 0.05) on survival rate. The heritability estimates of survival rate were low and ranged from 0.04 to 0.08 for autosomal, 0.01 to 0.02 for sex linked and 0.01 to 0.02 for maternal additive genetic effects. The estimates of autosomal, sex linked and maternal genetic correlations of survival rate in different ages were high. The overall mean of autosomal and sex linked breeding values of survival rate were greater than zero and increased by age of lamb. The Pearson and Spearman correlation coefficients between autosomal breeding values and sex linked breeding values in survival rate at different ages were 0.20 0.54 and 0.18 0.53 respectively. Thus, lamb survival rate up to yearling can be improved by farm management practices and improving environmental factors. Based on the genetic parameters estimated, the response to genetic selection would be slow, but would also be cumulative. However, genetic analysis using linear models which able to estimate genetic variation and breeding values in autosomal, sex linked and maternal separately, could be more effective to improve survival rate in lambs.