The Salmonella bacteria is a serious cause of disease in calves and cows. It most often presents as diarrhoea – in an individual animal or as an outbreak, with many animals falling sick.
There are thousands of different strains of Salmonella: typhimurium, bovismorbificans, zanzibar, anatum, dublin and newport are the most common strains we’ve cultured from cows and calves here in Southwest Victoria.
What are the signs of Salmonella?
Clinically affected animals generally present with diarrhoea, depression, dehydration, and fever. The diarrhoea can be watery or mucoid and may contain gut lining and/or blood. It usually smells terrible. The diarrhoea is also filled with Salmonella bacteria, and is a source of contamination of the animal’s surroundings.
As well as affecting the intestines, Salmonella is very good at travelling through the blood stream to other parts of the body. Cows can shed the bacteria in their milk and, if pregnant, may abort due to infection of the placenta.
Calves affected by Salmonella dublin (particularly those 6–12 weeks of age) may show respiratory disease, joint infections, jaundice, blood poisoning or may just die suddenly. These calves will shed bacteria in their saliva and nasal secretions as well as in their faeces.
Infected cattle can also become chronic carriers and shedders of Salmonella. This shedding – in faeces, milk, and saliva – may be all the time or intermittently when animals are stressed.
If you suspect Salmonella, it is important to confirm the diagnosis either by faecal culture or by testing samples from a post-mortem
These three very different scours were all caused by Salmonella. Sending faecal samples away for culture is the best way to confirm infection and identify the type of Salmonella that is causing disease.
How do cows get Salmonella?
In dairy cows, infection occurs when they ingest feed, pasture or water contaminated with infected faeces. Salmonella may arrive on a farm from purchasing infected cattle or contaminated feed, or from the movement of other animals such as birds and rodents. It can survive for months to years in cool, damp conditions.
The volatile fatty acids in a normally functioning rumen inhibit salmonella growth. Anything that reduces a cow’s dry matter intake or increases the risk of ruminal acidosis will increase the risk of clinical disease, such as:
- Calving or transport
- Other diseases (such as milk fever, ketosis, metritis) or inadequate access to feed
- Water deprivation
- Heat stress
- Sudden ration changes or a low forage:concentrate ratio
How do calves get Salmonella?
Calves also become infected with Salmonella through ingestion, for example:
- Drinking milk/colostrum fromcows shedding Salmonella
- Drinking milk/colostrum contaminatedwith manure
- Ingesting feed and water contaminated by infected calves (or other animals such as rodents or birds – see photos below!)
- Licking/chewing other calves, or contaminated gloves, equipment and/or bedding
The strength of a calf’s immune system is crucial. Calves with failure of transfer of colostral antibodies are at much greater risk of falling sick and then dying if infected with Salmonella. The outbreaks of Salmonella dublin in weaned calves is thought to partly be due to the dip in their immune system as colostral antibodies wear off and they begin to generate their own.
Gut health is also important as the normal gut bacteria supress Salmonella growth. Sudden changes in total solids when feeding milk replacer, or other diseases such as cryptosporidia, can lead to Salmonella.
Salmonella and antibiotics: what are the issues?
Treatment of Salmonella in cows and calves involves isolation, antibiotics, anti-inflammatories, and fluid therapy. Antibiotics improve clinical outcome, and on occasion are used prophylactically.
Over recent years we have been diagnosing more and more mutant Salmonella strains that are resistant to one or more antibiotics. This antibiotic resistance occurs when Salmonella typhimurium mutates in a way that gives it a competitive advantage over other bacteria when in the presence of antibiotics.
In some scenarios, none of the antibiotics we have available are effective against the Salmonella strain and so prevention becomes vital.
Can you vaccinate against Salmonella?
Yes! Vaccination can reduce the occurrence and severity of clinical disease. Two Salmonella vaccines are available in Australia:
- Bovilis S protects against Salmonella strains typhimurium and dublin
- BUZ protects against Salmonella strains bovismorbificans, uganda and zanzibar
For other strains of Salmonella, such as newport, we can work out which of these two vaccines can provide cross protection. It’s essential to identify which Salmonella is present on farm prior to vaccinating so that the right product is chosen.
Animals require two initial vaccinations 3–4 weeks apart, followed by yearly booster vaccinations. Vaccinating cows at drying off will maximise antibodies in colostrum for calves.
Even if you have already diagnosed Salmonell in the past, it is good to monitor the strain/s of Salmonella on your farm to ensure the right vaccine is being used and to monitor for antibiotic resistance.
What else can be done to prevent Salmonella?
Vaccination is just one part of controlling Salmonella. It is important to maximise immunity and minimise exposure to reduce the risk of infection and clinical disease:
- Maintain a closed herd
- Quarantine sick animals (or any animals that are bought in)
- Minimise the opportunity for faecal contamination (by any animal!) of feedstuffs, water, and troughs
- Manage the transition period to reduce diseases such as milk fever and ruminal acidosis
- Ensure good colostrum management to maximise immunity of newborn calves and minimise the risk of contamination of colostrum
- Don’t feed waste milk to calves – especially from scouring cows or other sick cows (if these are carrier animals, they are more likely to be shedding Salmonella)
- Ensure an all-in-all-out system for calf housing, with cleaning, disinfection, and complete beddingchanges between groups of calves
- Reduce spread through other animals: control nuisance birds, rodents, feral animals, and flies
Can people catch Salmonella?
Yes. Salmonella is zoonotic, which means it can infect humans. It is important to protect your staff and family:
- Do not drink milk out of the vat
- Always wear gloves when handling and treating cattle
- Avoid children or visitors in the calf shed, and don’t let calves suck fingers
- Wash hands well before eating and drinking
- Keep soiled farm clothes, boots, and equipment out of the house
- Be particularly cautious with pregnant or immunocompromised staff and family