Mortalities in sheep transported by sea

Deposited with permission of the author. © 1995 Dr. Andrew Philip KellyMajor animal welfare concerns existed about mortalities which occurred among the two million sheep transported by sea from Victoria, Australia to the Middle East each year during the 1980s. Research was undertaken to better define the extent of the mortalities, to establish the causes of death, and to prioritise and methodically unravel the underlying causes and risk factors involved. An analysis of five years of existing industry data on 100 sheep shipments from Victoria (1984/85-1988/89) showed that mortality rates ranged mostly between 1% and 4%, with an average of around 2 ½%. These analyses also showed that sporadic episodes of sudden, high mortality occurred in association with hot and humid conditions in Middle Eastern waters. Heat stress was the presumptive diagnosis. While the occurrences were rare, they accounted for 9% of all deaths. Observational studies undertaken on 8 research voyages with sheep to the Middle East showed that two other causes of death – an inanition syndrome and salmonellosis – accounted for the majority of all mortalities. Together, these two conditions caused around three quarters of all deaths. The following risk factors associated with these two major diseases were identified: poor feeding behaviour in the assembly feedlot; physiologic stress at the point of arrival of sheep at the feedlot; and the physical location of sheep on board ships, whereby sheep in the upper tier of pens on every deck of a ship suffered substantially higher mortality rates than those in the lower tier. Specific studies on the inanition syndrome showed that affected sheep were persistent poor consumers of the pelleted shipboard ration. A problem of severe weight loss was detected in an additional 5% of sheep, which appeared to be associated with inanition. Sheep with the syndrome still had an appetite for familiar food such as hay. An hypothesis was developed that the syndrome may be caused by the failure of affected sheep to recognise or accept the pelleted ration as food. The epidemiology of salmonellosis outbreaks in the live sheep trade was elucidated. The outbreaks occurred as rise and fall epidemics starting with a large increase in faecal salmonella excretion from sheep immediately after their arrival in the assembly feedlot near the port of embarkation. Epidemics of mortalities from salmonellosis peaked one to two weeks later, then declined before the voyage was completed. Evidence was obtained that salmonella infections persisted in the feedlot environment between consecutive batches of sheep initiating new epidemics in subsequent consignments. The differences in shipboard mortality rates between upper and lower tier pens (the “tier’ effect) was investigated with observational studies and a major field trial. An hypothesis that the effect was caused by higher light intensity in upper tier pens was tested and rejected. A remaining hypothesis is that the sheep’s fear of elevation in upper tier pens may be the cause. Overall, the research has advanced knowledge substantially on animal health in the live sheep trade. The findings will influence the debate on animal welfare in the trade, they will be of practical use to the industry, and they have focussed research direction for the future