Milad Noorian - Department of Animal Science, Science and Research Branch, Islamic Azad University, Tehran, Iran
Sahereh Joezy-Shekalgorabi - Department of Animal Science, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran
Nasser Emam Jomea Kashan - Department of Animal Science, Science and Research Branch, Islamic Azad University, Tehran, Iran.

The objective of this study was to estimate genetic parameters for sexual dimorphism (SD) in birth weights (BW), weaning weights (WW), ۶-month weight (W۶), ۹-month weight (W۹) and ۱۲-month weight (W۱۲) of Baluchi sheep. Data were collected during ۱۹۸۱-۲۰۱۵ from Baluchi sheep flock (flock no ۱) of Abbas Abad sheep breeding station located in Mashhad, Iran. Data were included ۷۳۳۹, ۷۳۰۳, ۵۸۸۴, ۵۱۶۲ and ۴۶۹۱ records of birth weight, weaning weight, ۶-month weight, ۹-month weight and ۱۲-month weight, respectively. Six bivariate animal models were used to estimate variance components and corresponding genetic parameters in male and female lambs separately. The SD levels (ratio of Male/Female) increased from ۱.۰۶ at birth to ۱.۱۳ at yearling age. Except for W۹ in which additive genetic variance and direct heritability (h_a^۲) were greater in males, for the other studied traits, females experienced higher additive genetic variance and h_a^۲. In both sex, maternal effects contributed significantly in phenotypic variation of body weights with greater contribution to body weights measured early in life. While in females, maternal genetic effect was greater than males, in males, maternal permanent environmental effect was greater which together with higher estimates of residual variances revealed greater sensitivity of male lambs to environmental conditions. Cross-sex additive genetic correlation (ra) was ۰.۸۶ for BW and ۱.۰۰ for the other studied traits. Maternal correlations between sexes were close to ۱.۰۰ indicating lack of sexual dimorphism for maternal effects on body weights of Baluchi lambs. Based on an approximate ۹۵% confidence interval, the difference between sexes regarding direct heritability were not significant, indicating no need or opportunity for different selection strategies in two sexes. Therefore, a model including lambs of both sexes and with sex effects included in the model can be used for genetic evaluation.

body weight, heritability, sexual dimorphism, sheep