Study of sexual dimorphism in growth traits of Sangsari lambs: between-sex heritability and correlations

This research examined the genetic aspects of sexual dimorphism (SXD) regarding body weights at birth (BW), weaning (WW), ۶ months (۶MW), ۹ months (۹MW), and ۱۲ months (۱۲MW) in Sangsari sheep. The records were retrieved from a dataset collected between ۱۹۸۶ and ۲۰۱۶ at the Sangsari sheep breeding station. The PROC GLM was applied to evaluate the environmental factors. The SXD levels were calculated as the average of male/female ratios at birth, weaning, six, nine and ۱۲ months of age. Genetic analysis was accomplished using the AI-REML method of the WOMBAT software. Six univariate and bivariate animal models were employed for the genetic assessment of traits in combined sexes, as well as for male and female lambs separately. Male lambs weighed more than female lambs, with a weight difference of ۰.۲۱ kg (۷.۲۲%) at birth increasing to ۳.۹۱ kg (۱۳.۹۵%) at ۱۲ months of age. Levels of SXD were relatively low, ranging from ۱.۰۷ for BW to ۱.۱۶ for ۱۲MW. For all traits except ۱۲MW, the  σ_a^۲, σ_e^۲, σ_P^۲, h^۲, and CV_a were higher in male lambs than females. Direct heritability estimates for BW, ۳MW, ۶MW, ۹MW, and ۱۲MW in male lambs were ۰.۲۸, ۰.۱۷, ۰.۲۰, ۰.۱۶, and ۰.۱۸, respectively. The corresponding estimates for female lambs were ۰.۲۷, ۰.۱۷, ۰.۱۶, ۰.۱۳, and ۰.۲۳, respectively. Direct genetic correlations (rg) between the sexes ranged from ۰.۸۹ for ۶MW to ۱.۰۰ for ۹MW and ۱۲MW. Cross-sex maternal permanent environment correlations (rpe) were ۰.۷۱ for ۶MW and ۰.۹۸ for ۳MW and ۹MW. These results indicated that ۶MW was the most dimorphic trait in the Sangsari lambs. High and positive genetic correlations between the sexes suggested that selection for body weight in males would result in a correlated response in females and vice versa, thereby preventing phenotypic divergence.

کلیدواژه ها:

body weight ، cross-sex correlation ، heritability ، maternal effect ، sheep