Phenotypic and genetic characteristics of longevity in Lori-Bakhtiari sheep

Longevity records of 978 Lori-Bakhtiari ewes were collected from a research flock at the Lori-Bakhtiari sheep breeding station during 1989 to 2006. Single-trait animal model used to analyze trait, included fixed effects of year of production, ewe body weight as covariable and random effects additive genetic of animal and residual effects. Phenotypic and genetic trends were estimated as regression of average phenotypic value and breeding value by birth year of ewe. Results show that, 49.80%, 22.49% and 27.71% of breeding ewes left the flock for illness, low production and oldness respectively. The overall mean (± s.e.) of ewe's longevity was 1779.91 (22.10) days. The effect of year of production and ewe's body weight on longevity were significant (p<0.01), and longevity increased by 41.84 ± 2.80 days with 1 kg of ewe body weight. Estimation of heritability for longevity was 0.33 ± 0.07. The phenotypic and genetic trends of longevity were significant (P<0.01) and estimated as -84.65 and -19.02 days, respectively. Thus, illness is very important reasons to removed ewes from flock. Longevity could be improved by selection, but early life traits is needed to indirect selection for longevity.