At this time of year, salmonella can be quite topical simply because of the high risk for salmonella abortion. I have also received a lot of questions in relation to high salmonella readings on bulk milk samples over the last month. For this reason, I think it is important to know how salmonella is spread and be aware of symptoms and control measures.

Salmonella is a bacteria with a number of species, which can affect animals as well as humans. For this reason alone, it is important to minimise exposure and risk to animals and farmers alike. It can also cause severe clinical signs when outbreaks occur and can be an extremely costly infectious disease on some farms. Interestingly, it has also been highlighted as one of the main infectious agents that can affect rapidly expanding dairy enterprises.

Salmonella can spread by two main routes:

  • Faecal/oral, which simply means that it can be ingested from the faeces of carrier or sick animals.
  • latent carriers – these are healthy animals that can start shedding salmonella due to stress. These will end up showing clinical signs and can also be a source of the disease for unexposed or naive cattle in the herd.

    • Salmonella is believed to be stored in the gall bladder of these carrier animals. Subsequently, when these animals come under stress, they will start shedding the bacteria in their faeces. Another important point with salmonella is that fluke infestation seems to leave animals much more exposed to spreading and developing clinical infection. So controlling fluke certainly can aid in salmonella control programmes.

    Abortions and scours

    Salmonella can cause a number of clinical signs. At this time of year, we will commonly see it linked to sporadic abortions or, in some cases, abortion storms.

    In adult cattle it can cause the usual symptoms of blood scours, severe dehydration, poor appetite and temperatures. It can also cause some more chronic conditions such as pneumonia or kidney infections in cows, which may be more difficult to diagnose as salmonellosis.

    In calves it can cause scours, septicaemia, dehydration, terminal dry gangrene or even spinal osteomyelitis.

    As is the case with most diseases, it is important to try and make a diagnosis quickly. Your own vet will discuss the options around diagnostics – be it faeces, blood, milk or post-mortems. Interpreting bulk milk samples with caution gives a fair indication of a widespread prevalence of salmonella.

    Simple measures

    Although this is a very costly disease, most farms can reduce their exposure risk with some simple measures.

    Biosecurity is the first step in controlling the risk of most infectious agents. This simply means stopping its introduction into a herd or, when this occurs, slowing down or minimising it spreading within the herd.

    The main source of any of these infectious agents is from buying in stock or increasing cattle movements. This is often the case with expansion and this is why salmonella poses such a risk to rapidly expanding herds. While it is not possible for all herds to operate a closed-herd programme, it is essential when buying stock that you minimise the risk. Buying stock from known sources or using diagnostics to pick up carrier animals may be an option. Boundaries should be maintained and all visitors should go through disinfection points. Sharing of equipment between farms and slurry spreading should also be tightly controlled. All feeds should be secure, with exposure to wildlife minimised.

    Vaccination is available for salmonella. Like most vaccines, this works best when given prior to the risk period. We will usually administer this around middle to late August. Like every vaccine, it can be expensive and your vet should be involved in drawing up a herd control programme.