Estimation of genetic parameters for reproductive traits in Mehraban sheep

Abstract

Genetic parameters for basic and composite reproductive traits in Mehraban sheep were estimated. Data included 10 257 records on reproductive performances of 5813 lambs from 69 sires and 603 dams which were collected from 1994 to 2011 in the Mehraban breeding station in Hamedan province, western Iran. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Test of significance to include fixed effects in the statistical model was performed using the GLM procedure of SAS. Genetic parameters were estimated with univariate and bivariate repeatability animal models using WOMBAT program. Direct heritability estimates were 0.16, 0.14, 0.03, 0.16, 0.06, and 0.18 for LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.02, 0.01, 0.73, 0.41, 0.27, and 0.03. The estimate for animal-dependent permanent environmental variance ranged from 0.01 ± 0.04 for LMWLW to 0.23 ± 0.04 for LSB. Genetic correlation estimates between traits ranged from −0.98 for LSB-LMWLW to 0.99 for LSB-TLWB. Phenotypic and environmental correlations were generally lower than genetic correlations. Phenotypic correlations ranged from −0.50 for LSB-LMWLB to 0.85 for LMWLW-TLWW. Environmental correlations ranged from −0.45 for LSB-LMWLB to 0.87 for LMWLW-TLWW. The results suggested that indirect selection based on TLWW could improve the reproductive performance in Mehraban ewes more effectively than if based on the other traits.

Genetic analysis of reproductive characteristics in Iran-Black sheep

“…The potential of ewes to produce lambs' birth weight regardless of the number of lambs born can be indicated by TLWB. In the present study, estimated direct heritability of TLWB (0.7) was in agreement with those reported by Rashidi et al (2011) in Moghani sheep. Direct heritability estimates for TLWB were reported in the literature and varied from 0.05 to 0.40 (Ekiz et al, 2005).…”

“…Direct heritability estimates for TLWB were reported in the literature and varied from 0.05 to 0.40 (Ekiz et al, 2005). The combined effects of reproductive and mothering ability of ewes, pre-weaning growth and survival of lambs are indicated by TLWW (Rashidi et al, 2011). Direct heritability estimate of TLWW in the current study (0.07) was consistent with those of Van Wyk et al (2003) and Ekiz et al (2005).…”

“…For Iran-Black sheep, the estimate of direct heritability of LSB (0.11) was similar with that reported by Rashidi et al (2011) in Moghani sheep. This value for LSW (0.05) was lower than LSB.…”

“…The highest value of direct heritability was obtained for LMWLB (0.33) including the possibility of genetic change in the trait to improve lambs' birth weight. Lower estimates were reported by Rashidi et al (2011) in Moghani sheep and Mokhtari et al (2010) in Kermani sheep. Also, direct heritability of LMWLW (0.11) was in agreement with the estimate of Vatankhah and Talebi (2008) in Lori-Bakhtiari sheep (0.10) but lower than estimates reported by Mokhtari et al (2010).…”

“…Therefore, using least squares analysis, the adjustment factors were determined for the effect of sex on birth and weaning weight of lambs. Estimates of variance components and consequently genetic parameters were achieved by the Restricted Maximum Likelihood (REML) method applying a univariate repeatability linear model (Rashidi, Mokhtari, Esmailizadeh, & Fozi, 2011;Vatankhah & Talebi, 2008) using DMU 4.7 package (Madsen& Jensen, 2007), fitting the following univariate models for each trait as:…”