Salmonellosis is a bacterial disease that is characterised by outbreaks of severe diarrhoea and death.
In sheep there are two forms of the disease seen. The enteric form and the reproductive form. The enteric form is caused by Salmonella hindmarsh, Salmonella typhimurium and Salmonella bovis-morbificans. The reproductive form is caused by Salmonella Brandenburg, although on rare occasion S. Brandenburg can also cause an enteric disease in non-pregnant sheep.
Generally the enteric form is seen between December to June, probably due to the increased stress associated with mob stocking and rotational or intensive grazing.
Carrier animals are regarded as the source of any outbreak but clinical disease only occurs as a result of some stress factor, such as:
A sudden change in nutrition to poor feed.
Holding stock in yards over long periods (>24 hrs)
Transport over long distances
Holding sheep at high stocking rates
The normal clinical presentation is to suddenly find a few ewes dead every few days when mobs are shifted. The mortality rate is usually about 1% but can exceed 5% on rare occasions. Many ewes will show no signs prior to death but some will be observed with a karki coloured diarrhoea that adheres to the wool on the hocks and crutch.
Post mortem examination reveals severe inflammation of the abomasum and the intestines with enlargement of the mesenteric lymph nodes. Confirmation can be made by culture of the gut contents.
Salmonella is a zoonotic disease, therefore care must be taken when handling both the sick and dead animals in order to prevent human infections.