Investigation of factors which affect lori-Bakhtiari lambs mortality from birth to weaning

The aim of this study was identification of important factors and their effects on mortality of Lori-Bakhtiari lambs from birth to weaning. The data set used for statistical analysis were collected from 4991 lambs born between 1370 and 1384 in flock at Lori-Bakhtiari sheep breeding station. Data was modeled using logistic regression. Mortality variable as dependent and ewe weight at mating، ewe age، lamb birth weight، lamb sex، year of birth and decade of birth as independent variables interred to the model. Odds ratios in addition to regression coefficients were derived for continued variables and each level of non-continued variable with respect to first level of that variable. According to results، year of birth، decade of birth and birth weight had very significant effects on lamb mortality. Mortality probability of lambs born in the initial month of parturition period was lower than mortality likelihood of lambs born in the end month of parturition and spring born lambs. Male lambs’ mortality likelihood was 1. 5 times higher than mortality likelihood of female lambs. Furthermore، mortality likelihood of lambs of 5-year-old ewes was lower than mortality likelihood of lambs born in younger and older ewes. Mortality probability from birth to weaning decreased due to each unit increase in lamb birth weight but by each unit increase in ewe weight at mating، mortality rate of lambs partially increase