Genetic analysis of sexual size dimorphism in growth traits of Kermani sheep

Genetic differences in expression of traits between sexes can be applied for developing efficient genetic evaluation of animals. The aim of the present study was to investigate the existence of sexual dimorphism (SD) in birth weight (BW), weaning weight (WW) and six months weight (6MW) and also correspondingly the genetic analysis of SD in male and female Kermani lambs applying pedigree information and records, collected from 1993 to 2013 in Breeding Station of Kermani sheep,. The SD values, defined as mean body weight of male lambs to mean body weight of female lambs were 1.04, 1.09 and 1.13 for BW, WW and 6MW, respectively. Six bivariate animal models, contained different combinations of direct additive genetic, maternal additive genetic and maternal permanent environmental effects, were used for genetic analysis of SD. Each body weight traits were considered as distinct traits in male and females. The considered bivariate animal models was evaluated via Bayesian Information Criterion (BIC). Direct heritability estimates for BW, WW and 6MW in male lambs were 0.11, 0.35 and 0.32, respectively. The corresponding estimates in female lambs were 0.10, 0.36 and 0.23, respectively. Cross-sex genetic correlations for BW, WW and 6MW were 0.92, 0.93, and 1.00, respectively. High and positive genetic correlations indicated that the studied traits in male and female lambs are control by common genes. Due to high and positive cross-sex genetic correlations for the studied body weight traits it may be concluded that selection in male lambs would result in a positive correlated response in females.