Climatic influences on the mortality of sheep during long-distance sea transport.
Research on the causes of sheep death in sea voyages from Australia to the Middle East is limited, in particular little is known about the influence of climatic factors. Mortality data from 417 shipments of sheep exported over an 11-year period (November 2004 to June 2015) were modelled retrospectively to determine associated climatic factors. The statistical analysis were performed for both the full data set with 417 voyages based on actual and estimated departure and arrival dates and a restricted data set with 71 voyages based on actual dates. The results of the full data set demonstrated a seasonal mortality pattern, with more deaths occurring on sea voyages leaving Australia in the southern hemisphere winter or spring than those departing in Australian summer or autumn. Heat stress and inadequate fat mobilisation for energy supply when sheep are inappetant on shipments may explain this seasonality. Based on these two models, the voyage and weather factors associated with sheep mortalities included departure year, autumn departure in the southern hemisphere, voyage duration, single or multiple loading port(s), weekly mean dry bulb temperature and wind speed at departure ports, and humidity at destination ports. Significant correlations were observed between weather variables at the departure ports in the Australian winter and a high sheep mortality rate during voyages. This, together with the anticipated increased heat stress risk as a result of climate change, suggests that there could be review of the trade from Australia in the southern hemisphere winter. The influence of weather at the departure ports should be considered in sheep mortality prediction models, especially Australia's heat stress risk assessment model.