Heritability estimates and correlations between production and reproductive traits in Lori-Bakhtiari sheep in Iran

Heritablities and correlations were estimated between lamb body weight at different ages and reproductive traits in the Lori-Bakhtiari sheep breed. Data and pedigree information for Lori-Bakhtiari sheep used in this study were 5826 records of body weight of lambs from 240 sires and 1627 dams, and 5741 records of reproductive traits from 1797 ewes collected from 1989 to 2006 from a Lori-Bakhtiari flock at the Shooli station in Shahrekord. The lamb traits investigated were weights at birth (BWT), weaning (WWT) and at six months of age (WT6). The reproductive traits were conception rate (CR), litter size at birth per ewe lambing (LSB/EL), litter size at weaning per ewe lambing (LSW/EL), litter size at birth per ewe exposed to a ram (LSB/EE), litter size at weaning per ewe exposed (LSW/EE), total litter weight at birth per ewe lambing (TLWB/EL), total litter weight at weaning per ewe lambing (TLWW/EL), total litter weight at birth per ewe exposed (TLWB/EE) and total litter weight at weaning per ewe exposed (TLWW/EE). (Co)Variance components and genetic parameters were estimated using the restricted maximum likelihood procedure applying three multi-trait animal models. The estimates of direct heritability for lamb body weights were 0.31 ± 0.02 at birth, 0.10 ± 0.02 at weaning and 0.19 ± 0.02 at six months of age, and estimates of maternal heritability were 0.22 ± 0.02, 0.16 ± 0.02 and 0.04 ± 0.02, respectively. The estimates of heritability for reproductive traits varied from 0.02 ± 0.01 for CR to 0.23 ± 0.01 for TLWB/EL, and repeatability estimates for reproductive traits ranged from 0.11 for CR to 0.28 for LSB. Genetic correlations among lamb body weight and various reproductive traits were positive and varied from 0.06 to 0.98. Phenotypic correlations were lower than genetic correlations (0.01 to 0.20). The estimates of genetic correlations between lamb body weight with CR and litter size at birth and at weaning were low to moderate, while those between lamb body weight with TLBW and TLWW per ewe lambing and per ewe exposed were positive and very high. Thus, lamb body weight at weaning or at six months of age could be considered as selection criteria to indirectly improve reproductive traits in Lori-Bakhtiari sheep because the heritability of lamb body weight was more than that of reproductive traits and can be measured at an early stage in the life of the animal. Keywords: Genetic correlations, early growth traits, reproductive traits South African Journal of Animal Science Vol. 38 (2) 2008: pp. 110-11