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While we all spend time with family these holidays, we thought we’d talk about our LEAST favourite family – Salmonella. This bacteria is a serious cause of diarrhoea in calves and cows (and lots of other animals for that matter – including us!)

How does Salmonella show up?

Clinically affected animals present with diarrhoea, depression, fever and dehydration – for any of you who’ve suffered food poisoning you can imagine what it feels like! The diarrhoea can be watery or mucoid and can contain fibrin and blood – it also smells terrible. Sometimes individual animals fall sick, other times outbreaks can occur, with many animals affected.

Sometimes Salmonella gets into the blood stream (sepsis). Calves may show respiratory disease, joint infections or die suddenly – and they will shed bacteria in their saliva and nasal secretions. Cows may shed the bacteria in their milk and may abort if pregnant due to infection of the placenta.

Sometimes infected cattle become chronic carriers of Salmonella, shedding it in their faeces and milk. This shedding may be all the time or occur intermittently (such as at calving).

How do animals get infected with Salmonella?

In dairy cows, infection occurs through ingestion of feed or water contaminated with infected faeces. Salmonella may arrive on a farm from purchasing infected cattle, from contaminated feed/water or the movement of other animals such as birds. The bacteria can survive for months to years in cool, damp areas.

Salmonella is usually killed by the volatile fatty acids (VFAs) produced in a normally functioning rumen. Anything that reduces dry matter intake may precipitate disease, such as:

  • Calving
  • Transport
  • Disease (such as milk fever, ketosis)
  • Sudden ration changes
  • Inadequate access to feed
  • Lack of water

Dairy calves become infected with Salmonella by:

  • Drinking infected milk/colostrum from cows shedding Salmonella
  • Drinking milk/colostrum contaminated with faeces
  • Ingesting feed, water or bedding contaminated by infected calves
  • Licking other calves or equipment contaminated with saliva

Are there different types of Salmonella?

There are more than 2500 different individual Salmonellas across the world occurring in a multitude of animal species. Salmonella is divided into 50 “families” with a few associated with most of the disease occurrence.

Under the microscope, Salmonella is a rod-shaped bacteria, with little protein tails called flagella that help it move around. The cell wall of Salmonella is made up polysaccharide “bricks” and the pattern of these bricks is what determines what family the Salmonella falls into. The type of protein in the flagella tail is what determines the individual Salmonella type (called a serovar).

There are many different Salmonellas that can infect cows and calves: typhimurium, bovismorbificans, zanzibar, anatum, dublin and newport are the most common serovars we’ve cultured from cows in our district. We are also finding more and more mutant salmonellas (that don’t have specific names) that are resistant to multiple antibiotics.


Can you vaccinate against Salmonella?

Yes! Vaccination can reduce the occurrence and severity of clinical disease. But there are some important things to note:

  • Two Salmonella vaccines are available in Australia, protecting against the most commonly isolated serovars
  • Bovilis S protects against B and D family Salmonellas (typhimurium and dublin)
  • BUZ protects against C and E family Salmonellas (bovismorbificans, uganda and zanzibar)
  • The vaccines should provide cross protection against other Salmonellas in those families – for example, Salmonella newport is in family C, so you would vaccinate with BUZ
  • Animals require two initial vaccinations followed by yearly booster vaccinations
  • Vaccinating cows at drying off will maximise antibodies in colostrum for calves

Vaccination is just one part of reducing Salmonella disease. It is important to maximise animal immunity and minimising exposure to reduce the risk of infection and clinical disease:

  • Maintain a closed herd
  • Quarantine sick animals
  • Ensure an all-in-all-out system for calf housing, with cleaning, disinfection and complete bedding change between groups of calves
  • Minimise opportunity for faecal contamination of feedstuffs, feeding surfaces, water troughs and equipment
  • Good transition management for cows to minimise diseases and ensure dry matter intake
  • Colostrum management to maximise newborn calf immunity
  • Reduce spread though other animals: control nuisance birds, rodents, feral animals, flies

Salmonella – some key points:

  • If you suspect Salmonella, it is important to confirm the diagnosis: we have faecal sampling kits with instructions at our clinics for you to have on hand as needed
  • We send samples away to the lab to identify which Salmonella “family” is causing disease and whether any antibiotic resistance is present. Positive samples will need to be sent to a different lab to identify the individual Salmonella serovar
  • It is important to identify which Salmonella family you have on your farm prior to vaccinating
  • Salmonella is zoonotic, which means it can infect humans. Hygiene is vitally important!

If you have any questions about Salmonella, please talk to one of our veterinarians.