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

Abstract

This research investigated the genetic and phenotypic characteristics of sexual dimorphism (SD) for body weights at birth (BW), weaning (WW), 6 months (6MW), 9 months (9MW), and 12 months (12MW) in Sangsari sheep. The records were retrieved from a dataset collected between 1986 and 2016 at the Sangsari sheep breeding station. The GLM method in the SAS program was applied to evaluate the environmental factors. The genetic analyses were accomplished using the AI-REML method of the WOMBAT software. Six bivariate animal models without or with maternal effects were used for genetic assessment traits in male and female lambs. Male lambs weighed more than female lambs and a weight difference of 0.21 kg (7.22%) at birth increased to 3.91 kg (13.95%) at yearling age. Levels of sexual dimorphism were relatively low and varied from 1.07 for BW to 1.16 for 12MW. For all traits except 12MW, \({{\sigma }}_{\text{a}}^{2}\), \({{\sigma }}_{\text{e}}^{2}\), \({{\sigma }}_{\text{P}}^{2}\), \({\text{h}}^{2}\), and \({\text{C}\text{V}}_{\text{a}}\) were higher in male lambs. Heritabilities for BW, 3MW, 6MW, and 9MW in male lambs were 3.18%, 4.53%, 24.05%, and 18.97% more than female lambs. For 12MW, the heritability of females was 23.83% more than males. Direct genetic correlations (rg) between the sexes ranged from 0.89 for 6MW to 1.00 for 9MW and 12MW, indicating that selection for body weight in males would result in a correlated response in females and consequently, would prevent phenotypic divergence. Cross-sex maternal permanent environment correlations (rpe) were 0.71 for 6MW and 0.98 for 3MW and 9MW. The values of rg and rpe for 6MW differed from 1.00, implying the presence of sexual dimorphism for additive genetic effects and maternal effects on 6MW.