The investigation of non-genetic factors affecting survival of Karakul lambs from birth to one year of age using linear and nonlinear models

The data used in this study were 6426 records of Karakul lambs' length of life and survival rate from 228 sires and 1894 dams collected from year 1992 to 2009. Linear and hazard ratio models with Weibull function were used in the analyses. Factors included in the models were non-genetic factors of year and month of birth, sex of lamb, type of birth and age of dam and lambs' birth weight fitted as linear and quadratic covariate. Results showed that the overall mean of lamb's life length and cumulative survival rate up to yearling were 274.32 days and 85.43%, respectively. The effect of year, month and type of birth, sex of lamb and lamb's birth weight as linear and quadratic covariates were significant (P < 0.01). However, the effect of age of dam on length of lamb's life and survival rate was not significant (P > 0.05). The survival rate and hazard ratio of lambs born in the first and second lambing month were higher and lower than the third month, respectively. The male lambs had lower survival rate and higher hazard ratio compared with females. Lambs with average birth weight had higher survival rate and lower hazard ratio than lambs with low and high birth weight. Although, lambs born from younger and older dams tended to have lower survival rate and higher hazard ratio, but they had not any significant differences with lambs born from middle age dams. Twin lambs had lower survival rate and higher hazard ratio than single lambs. According to the results obtained in this study, analyzing the effect of non-genetic factors on length of life and survival rate of lambs with linear and survival models produced the same result and these models can be used interchangeably. (C) 2013 Elsevier B.V. All rights reserved.