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A genetic study on sexual dimorphism of bodyweight in sheep

Ghafouri-Kesbi, Farhad, Mianji, Ghodratollah Rahimi, Pirsaraei, Zarbakht Ansari, Hafezian, Seyed Hasan, Baneh, Hasan, Soleimani, Bijan
Animal production science 2015 v.55 no.1 pp. 101-106
animal models, birth weight, chromosomes, females, genetic correlation, heritability, lambs, males, maternal effect, pedigree, sexual dimorphism, sexual selection, sires, variance, weaning
The aim of the present study was to investigate the genetic basis of sexual dimorphism of bodyweight in Zandi sheep. To do this, a pedigree including 1450 dams and 170 sires was used. Six bivariate animal models were applied for investigating direct and maternal effects for three age-specific bodyweights (bodyweight at birth, 3 and 6 months of age) in male and female Zandi lambs. The variance components were estimated via REML procedure. Males were, respectively, 6%, 7% and 9% heavier than females at birth, weaning and 6 months of age. Estimates of sexual dimorphism levels (expressed as M/F) were 1.11 at birth, 1.07 at weaning and 1.09 at 6 months of age, which indicated relatively low levels of sexual size dimorphism in the traits studied. Except for birthweight, for which estimates of additive genetic, residual and phenotypic variances as well as direct heritability and additive coefficient of variation were higher in females, for other traits studied, estimates were higher in males. However, regarding direct and maternal effects, none of the differences between the sexes was significant, indicating no need for sexual selection. Cross-sex genetic correlations were 0.862 at birth, 0.918 at weaning and 0.922 at 6 months of age, which highlighted birthweight as the most dimorphic trait. It was concluded that, owing to possible contribution of sexual chromosomes to variation of growth-related traits, bodyweight in male and female lambs may not be under the exactly same genetic control.