It is common for farms to experience outbreaks after a dry spell in the summer when the pasture freshens up in the autumn (post-weaning through to mid-pregnancy). It can also occur later in pregnancy.
Salmonella most often targets good conditioned two-tooth and mixed-age ewes and rams, and usually presents as sudden death. Disease is very rare in lambs and hoggets.
It causes an acute gastroenteritis (gut infection) leading to septicaemia (blood poisoning) and death. Sheep are often found dead near troughs or natural water sources. A watery, green (khaki) coloured diarrhoea often containing blood is also typical of the disease. It is not uncommon to lose two to three ewes per day.
Salmonellosis can be diagnosed by a post-mortem inspection +/- culture of the bacteria from the gut contents. Other diseases to consider are Clostridial disease, liver fluke, milk fever and plant poisonings.
Salvexin®+B vaccine is best used as a preventative measure but can also be used in the face of an outbreak. In either case, sheep should always be boosted with a second vaccination four weeks later to ensure long-term protection.
In future years, the flock should receive an annual booster vaccination two to three weeks prior to the risk period (which can be as early as December/January). Replacement breeding ewes (two-tooth) should receive two vaccinations four weeks apart annually prior to the risk period.
General recommendations are to remove stock from the paddocks in which deaths are occurring, and spread the flock out over the farm to reduce grazing pressure and pasture contamination. Affected farms can normally return to routine grazing practices after 10 days. A clean water source is also very important.
If you are experiencing ewe losses, please do not hesitate to contact your veterinarian for advice.