estimation of genetic, environmental and phenotypic trends for economic lifetime of the lori-bakhtiari ewes

in this study, the number of 1802 longevity records of ewes collected during 1989 to 2010 in breeding station of lori-bakhtiari sheep flocks were used to estimate of genetic, environmental and phenotypic trends for economic lifetime. the breeding values of a ewe’s lifetime were estimated by restricted maximum likelihood procedure under an animal model of univariate analysis. the best linear unbiased prediction of breeding values estimated and genetic trends were estimated as a regression coefficient of average breeding values on the birth year of ewes. the environmental and phenotypic trends estimated as a regression coefficient of average environmental deviation and phenotypic deviation (deviations of phenotypic values from overall mean) on the birth year of ewes. the results showed that, genetic trend of longevity was positive (0.033 days) but insignificant from zero. while the environmental and phenotypic trends were equal to -27.81 and -27.78 days, respectively, and significantly different from zero (p