Factors influencing Awassi lambs survivorship under fields conditions

The objective of this study was to investigate the pre-weaning survival rates of Awassi lambs and identify the causes of death in extensive and semi-extensive production systems. The study was designed to collect data under field conditions. Data were recorded on 29,290 lambs born alive during lambing seasons from 2011 to 2015. Postmortem autopsy findings were collected from 5448 lambs died during the pre-weaning period. About 63.5% of losses occurred during the first 7 days of life. The overall pre-weaning mortality rates were 19.7% and 16.9% in the extensive and semi-extensive production systems, respectively. Lamb birth weight had a strong effect (P < 0.0001) on the pre-weaning mortality rate. The mean mortality rate in lambs weighed < 2 kg at birth was 45.1%. The proportion of autopsied lambs dying by category was starvation (28.6%), respiratory infections (19.2%), gastrointestinal infections (16.2%), birth injuries (10.2%), hypothermia (8.6%), enterotoxaemia (8.2%), dystocia (4.4%) and predation (2.1%). Explanatory variables best used by Weibull model to estimate the hazard ratio (HR) of lambs falling into a certain death category were production system, lamb sex, birth type, and lamb birth weight. Lambs born in extensive production system were more (P < 0.0001) likely to die from starvation (HR = 4.6), gastrointestinal infections (HR = 3.2), and hypothermia (HR = 2.2), compared with semi extensive system. Lambs weighed < 2 kg at birth were more (P < 0.0001) likely to die from starvation (HR = 5.5), hypothermia (HR = 3.6), gastrointestinal infections (HR = 2.4) and respiratory infections (HR = 2.2), compared with lambs weighed 3-4 kg. Triplet lambs were 4.6 more (P < 0.0001) likely to die from hypothermia and 4.3 more (P < 0.0001) likely to die from starvation. Survival rates of Awassi lambs can be improved by applying appropriate management practices that target intermediate birth weights and minimize the infectious diseases, starvation and cold stress.