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Salmonella is a bacteria that can affect both humans and cattle. In cattle and other livestock, Salmonella usually manifests as either chronic or acute gut disease (diarrhoea), acute blood poisoning or as abortion. Consequently salmonella is a disease that can cause significant financial losses if an outbreak occurs. Unfortunately, we have had multiple outbreaks of Salmonella in South Waikato farms in the 2010 and 2011 seasons.

The predominant species of Salmonella isolated from cattle in New Zealand is Salmonella typhimurium.  However, many different types exist and we have isolated various serovars from affected cows in the past 2 years.

The most important sources of infection are clinically affected animals and carrier animals. Clinically infected animals will intermittently shed Salmonella organisms in their faeces. Carrier animals also play an important role in the spread of infection. These animals shed high numbers of salmonella into the environment at times of stress, but often do not appear ill, apart from perhaps having poor condition.

Contaminated water, feedstuffs and environments are other important sources of infection. Birds in calf meal bins, feed pads and in milking shed feed troughs will start new infections. Animals are primarily infected by ingestion.

Infections have previously been more common in young calves, but recently we have had multiple adult herd outbreaks.

Salmonella is a very hardy bacteria and has been shown to survive up to 2 years in the environment, however it is susceptible to sunlight and drying out.

There are a wide range of clinical signs such as:

  1. mild diarrhoea

  2. severe sudden diarrhoea with depression and marked fever. Blood, and shreds of gut lining may be in the diarrhoea. The faeces will usually be very smelly and fetid. Cows will usually be anorexic and will not drink resulting in severe dehydration. Death may occur with 48 hours.

  3. Pregnant cows infected with S. Dublin or S.Brandenburg strains may abort while showing clinical signs as above.

  4. Calves that are infected typically are 2 - 6 weeks of age. They develop fever, dullness, loss of appetite, brown pasty fluid diarrhoea which may contain sheds of mucosa. Some calves may show signs of blood poisoning, meningitis or polyarthritis with or without diarrhoea. Others may simply be found dead with no observed signs before death.

Diagnosis of Salmonella infection is usually achieved by using faecal cultures, and sampling of other tissues in recently dead or aborted animals. Any cow which has suspected (or proven) Salmonella should be isolated from the herd. These cows should be brought into the milking shed last away from other cows. Boots, hands, aprons and concrete flooring should be both washed and disinfected.

Early treatment of suspected cases is vital in survival of the animal. The use of broad spectrum antibiotics early will result in survival of the animal.  If treatment is delayed by as little as 48 hours, it can cause irreversible damage to the gut and severe dehydration resulting in death. If you have any suspected cases, please get vet attention as soon as possible.

Advanced cases may also require electrolytes orally or even intravenous fluid therapy. As these animals are running fevers, we often also given ant-inflammatories (Tolfedine).

Vaccination is a good option to reduce your chances of an outbreak. It’s also been shown that in cases where outbreaks occur that vaccination reduces severity of the disease when used in combination with other control measures. Vaccination is likely to be cost effective in an outbreak e.g. in the calf shed or amongst adults, but is less justified in sporadic cases.  Its ideal to make sure your cows are boosted every 12 months. This should be done between 8 and 3 weeks prior to calving. This will ensure adequate colostral transfer of antibodies to calf milk. Calves that are fed milk from cows vaccinated as above will not need to be vaccinated until 8 weeks of age.  Otherwise calves may be vaccinated at any age but must receive a booster 3 to 4 weeks later.

Please note that whilst the Salvexin+b vaccine we use protects your cattle against the four most common strains of Salmonella, there is no proven cross-protection against other strains. We strongly recommend vaccinating your herd against Salmonella, but keep in mind sporadic outbreaks of disease may still occur if an animal picks up a different strain.

Salmonella is a zoonotic disease. This means humans may catch Salmonella from working with affected cattle. Appropriate hygiene methods (such as wearing gloves) must be applied when handling potentially infected to stock to reduce the risk of human infection. Unpasteurised milk from an infected herd can also lead to transfer of disease to humans.

If you have any queries, please contact the clinic.

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