Salmonella

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 several common strains of 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 when adding 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 and supportive therapy will usually result in the improved outcomes for the animal. Delayed treatment can cause severe dehydration and irreversible damage to the gut, and can result in prolonged treatment periods and worse outcomes.

What causes Salmonellosis

Salmonellosis is caused primarily by ingestion of Salmonella bacteria, which can live for long periods of time in the environment (6+ months), making elimination of the organism difficult.

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, contributed to by intensification, higher stocking rates and/or higher use of supplementary feed.

Signs in animals

Different types of Salmonella lead to a variety of clinical signs. The most common signs to look for include:

• A sudden drop in milk production
• Diarrhoea - ranging from mild to severe and watery
• Loss of appetite
• Fever
• Dehydration
• Abortions can happen with some types of salmonella
• Death can occur in severe cases or if left untreated

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

In New Zealand, carrier animals are a significant source of 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. Some cows will carry the bacteria for life after an infection.

Clinical experience indicates that the risk of Salmonellosis increases when supplementation with magnesium (e.g. Mag oxide, Mag chloride), occurs at higher than recommended dose rates and with certain forms of delivery (e.g. prills).