Determination of the best birth weight for survival to weaning in Karakul breed lambs

To study the effect of non-genetic factors on survival of Karakul lambs from birth to weaning age 6,426 records collected from year 1992 through 2009 were used. Traits under study were cumulative survival from birth to 14, 30, 60 and 90 days of age. For each trait a linear model fitted which included the factors of lamb's year and month of birth, type of birth, sex, age of dam and birth weight (as linear and quadratic covariates). The GLM procedure of SAS software was applied. All the factors except for age of dam had significant effects (P<0.001) on traits. Mortality to weaning age in total, single and twins were 8%, 5.87% and 17.79% respectively. Hazard ratio of death from birth to 30d of age had increasing trend and after that till weaning showed decreasing one. In males and twins hazard of death was higher compared to females and single lambs. Average birth weight in singles and twins were 5.32(0.67) and 4.25(0.65) kg respectively. Optimum birth weight in which survival would be maximum in 14, 30, 60 and 90 days of age in singles and twins were 5.78, 4.68; 5.88, 4.86; 5.93, 5.03 and 5, 5.93 kg respectively. Optimum birth weight in which survival would be maximum in 14, 30, 60 and 90 days of age in male and female lambs were 5.9, 5.4; 6.1, 5.6; 6.4, 5.6 and 5.9, 5 kg respectively. It can be suggested that in order to develop the survival of Karakul lambs we select lambs on the basis of the optimal birth weight instead of the higher one.