The survival analysis of some environmental factors associated with lamb mortality in Awassi sheep

Most of the economic losses in the Turkish sheep industry are due to lamb deaths between birth and weaning period. Survival analysis is an essential step in the understanding of the lamb’s survival function and the hazards that have an impact on mortality. The lamb records were accessed from 2013 to 2019, with the information of 11,523 lambs from birth to weaning at 90 days of age. The Kaplan-Meier method was used for the estimation of the survival function of the lambs. The Cox proportional hazards survival analysis was performed to evaluate the factors influencing Awassi lamb mortality in the central Anatolian region of Türkiye. A multivariable Cox regression was fitted to the data after checking the assumptions of the regression. Year of birth, lambing season, lamb sex, method of birth, and birth weight groups were used as explanatory variables. The overall survival of the lambs to weaning was 75.7%, and the Kaplan-Meier estimate of the average survival time to weaning was 62.25 days. Cox proportional hazards modeling showed that the hazard rate of death before weaning was higher in male lambs (1.205 and 95% CI, 1.119–1.300) compared to female lambs. It was also noted that the hazard rate of death (HR = 0.956 and 95% CI, 0.937–0.974) had significant years. The single-born lambs had a lower risk of death among the lambs. The summer and autumn seasons had a very highly advanced effect on the survival rate of the lambs. The hazard rate for the categorical birth weight group was 0.703 (95% CI, 0.667–0.741). This indicates that the risk of pre-weaning mortality decreased with increasing birth weight > 3.5 kg. The results of this study showed that lamb survival can be increased by paying more attention to winter born lambs, male sex, twin births, and lambs about birth weight (< 3.5 kg).