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What causes Salmonellosis Signs in animals How is it spread? Management of Salmonella

Salmonellosis is a common disease causing acute diarrhoea in adult dairy cows and can also affect humans. It's mainly caused by ingestion of Salmonella bacteria from affected cows, contaminated environments, and infected water or feed. This disease is increasing in New Zealand, mainly due to higher stocking rates and supplementary feeding. Typical symptoms in cows include sudden drop in milk production, loss of appetite, diarrhoea, and fever. In severe cases, it can cause death. Spreading occurs through direct contact, dirty objects, contaminated feed or water, and untreated effluent on pastures. Prevention methods include vaccination, good biosecurity, appropriate effluent management, and strict hygiene practices.

Salmonellosis is the most common disease associated with acute diarrhoea in adult dairy cows. Salmonella bacteria from cattle can also be transferred to humans, causing illness and disease.

What causes Salmonellosis

Salmonellosis is caused primarily by ingestion of Salmonella bacteria, which can live for long periods of time in the environment (~28 weeks).

There are a variety of types or serovars of Salmonella bacteria that can affect dairy cattle. Salmonella typhimurium and Salmonella bovismorbificans are the most common in New Zealand.

The occurrence of Salmonella is increasing in New Zealand, in parallel with a world-wide trend, largely as a result of intensification, higher stocking rates and/or higher use of supplementary feed.

The most common sources of Salmonella include:

  • Other clinically affected cows or carrier animals
  • Contaminated environments
  • Water or feed that has been contaminated with faeces

Signs in animals

Different types of Salmonella lead to a variety of clinical signs.

The most common signs to look for include:

  • Sudden drop in milk production
  • Loss of appetite
  • Diarrheoa and/or dysentery
  • Animals presenting as anorexic, with a fever
  • Dehydration
  • Abortions can happen with some types of salmonella
  • Death can occur in severe cases or if left untreated

If your animals are experiencing any of the signs listed above, seek immediate advice from your vet.

How is it spread?

Salmonella can be spread by several different means, including:

  • Direct animal-animal contact within the herd
  • Other animals or birds
  • Dirty clothing/objects
  • Contamination of feed or water supply
  • Airborne bacteria
  • Application of untreated effluent to pastures

The long period over which Salmonella can persist in the environment (up to 28 weeks) makes elimination of the organism difficult.

In New Zealand, carrier animals are the leading means of spreading infection, especially as re-shedding of infection can be brought on by stressors such as calving, transportation, bad weather or deprivation of food or water.

Salmonella can be spread between species, and is also a zoonotic disease, meaning that it can transfer between cows and humans.

Clinical experience indicates that the risk of Salmonellosis increases when supplementation with magnesium e.g. Mag oxide, Mag chloride, occurs at above recommended dose rates.

Management, prevention and control of Salmonella

Prevention should focus on reducing the risk of infection, minimising the spread of infection, and enhancing the immunity of animals within the herd.

Such measures include:

  • Vaccinating against Salmonella – vaccination programmes are an effective way of protecting the herd against Salmonellosis, and can be helpful in reducing the number of sick cows even once an outbreak of Salmonellosis occurs in a previously unvaccinated herd
  • Good biosecurity procedures for any new animals to the herd
  • Appropriate storage and application of effluent, with a minimum stand-down period between application and grazing
  • Effective rodent and bird control, particularly around feed bunkers and grain silos
  • Good hygiene practices at milking time, and procedures on-farm to help protect staff
  • Wearing gloves while working with cattle, particularly around calving
  • Cleaning and drying gear regularly to reduce the risk of contamination

If cases do occur, it is important to seek veterinary advice promptly. Early treatment of cases with broad spectrum antibiotics will usually result in the survival of the animal. Delayed treatment (~48 hours) will result in severe dehydration and irreversible damage to the gut. Treating these cases will require supportive therapy, which may improve the chances of recovery, however this is likely to be a lengthy process.

Last updated: Sep 2023
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