Last year recorded the most cases of Salmonellosis for the past 15 years of surveillance, with over 50 cases reported in the Manawatu.
The majority of these cases were caused by strains of Salmonella that are included in the Salvexin®+B vaccine. Most outbreaks occurred around calving time (August-October) and in late autumn.
What can Salmonella do?
Salmonellosis in dairy cows can cause depression, and reduced appetites up to severe and often fatal, outbreaks of acute diarrhoea, fever, and abortions to unexplained deaths and can be devastating. It significantly impacts farm production and performance.
The disease is zoonotic, meaning it can be transmitted to humans through contact with faeces, contaminated equipment or milk, and it causes severe gastroenteritis, fever, diarrhoea, abdominal cramps, nausea, vomiting, and headache, so care should be taken when handling sick animals.
How does Salmonella get on farm and circulate through a farm?
Healthy cattle can carry Salmonella within the gut and it’s estimated that 9% of the herd are carrier animals at any time. These cattle can shed and spread the bacteria into the environment for months or even years. Sick animals shed very high numbers of Salmonella into the environment, furthering the spread of disease during an outbreak.
Salmonella bacteria can survive in the environment for a long period of time (e.g. months to years in ideal conditions like wet paddocks, effluent ponds, or dry, shaded areas such as cattle yards).
Farm outbreaks usually come from purchased cattle or cattle exposed off-farm or occur through a pre-existing subclinical circulation. Birds and fomites (carrier objects) can be responsible for the occasional incursion in a completely closed herd, but most likely Salmonella is introduced with livestock movements or from on-farm carrier animals.
Also, sudden dietary changes can lead to rumen upset, reduced volatile fatty acid production and stress which allows Salmonella to thrive and trigger Salmonella to come out of latency in carrier animals.
High-risk farms and situations include:
Large intensive farms; farms with recent history of clinical cases; farms within hotspot areas; farms that mix cattle (incoming and outgoing); high stress situations (especially following transport, fasting/dietary change, yarding, calving or those with disease e.g., BVD); farms sharing boundaries; farms feeding pelletised magnesium oxide, using continuous troughs in the shed and/or feeding palm kernel extract; and farms with no or partial vaccination programmes.
Also, the practice of grazing at-risk cattle on pastures sprayed with effluent is not advised. A problematic transition period can also put herds at risk. So, basically, most dairy farms are at risk.
Strategies that help prevent salmonellosis include:
Implementing dietary strategies that preserve normal gut pH and volatile fatty acid production; avoiding sudden dietary changes; minimising stress to high-risk cattle; and preventative vaccination with Salvexin®+B which is very effective at reducing clinical cases and stock losses.
What is the impact of a Salmonella outbreak?
In a 500-milking cow herd, with 10% sick and 2% deaths, the direct costs through dead cows and loss of milk can be over $30,000 (a conservative figure) in a single season.
This is not counting the milk out of supply, risk to humans, or impact on future production and reproduction. This far outweighs the cost of preventative vaccination for the herd.
Preventative vaccination strategies using Salvexin®+B
For dairy farmers, the best time to vaccinate cows is during late lactation or around dry off (not on the day of drying off).
Avoid giving the booster within four weeks of calving. Give two doses of Salvexin®+B four to six weeks apart under the skin. Salvexin®+B can cause a temporary drop in milk yield for the first day or two after vaccination so to minimise the impact on production, Salvexin®+B is best administered around the time of drying off, when udders are starting to involute and production is already dropping. It is advised not to give Salvexin®+B at the same time as other vaccines or treatments (e.g. Lepto/7-in-1), as this can reduce efficacy or increase adverse reactions and ensure cows are not vaccinated within 48 hours of transport.
Another positive to vaccinating cows with Salvexin®+B in late lactation/near dry-off, is that it increases antibody levels in colostrum, providing better passive immunity to newborn calves. In subsequent years, animals will require an annual booster.
Salvexin®+B is one of the cheapest restricted veterinary vaccines available. It protects against the three most common Salmonella strains in NZ (Typhimurium, Brandenburg, Bovismorbificans) but not against the emerging strain Salmonella Give.
