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), 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 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 12 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 0.21 kg (7.22%) at birth increasing to 3.91 kg (13.95%) at 12 months of age. levels of sxd were relatively low, ranging from 1.07 for bw to 1.16 for 12mw. for all traits except 12mw, the σa², σe², σp², h², and cva were higher in male lambs than females. direct heritability estimates for bw, 3mw, 6mw, 9mw, and 12mw in male lambs were 0.28, 0.17, 0.20, 0.16, and 0.18, respectively. the corresponding estimates for female lambs were 0.27, 0.17, 0.16, 0.13, and 0.23, respectively. direct genetic correlations (rg) between the sexes ranged from 0.89 for 6mw to 1.00 for 9mw and 12mw. cross-sex maternal permanent environment correlations (rpe) were 0.71 for 6mw and 0.98 for 3mw and 9mw. these results indicated that 6mw 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.