Salmonella is particularly important to identify and diagnose due to its zoonotic risk (it can cause severe illness in young children and the elderly – some strains have an up to 17% mortality rate in humans).
Impact Of Salmonella Outbreak To Your Herd
Financial impact is mainly through loss of milk yield. Estimates are between £6,000 up to £50,000 losses in the first year alone, with subsequent losses of up to £28,000 in milk yield in years post initial infection (Nielson et. al. 2013).
Salmonella is transmitted mainly by a faecal-oral route. It can be direct from cow to calf, or spread on clothing, aborted material and unpasteurised milk. Salmonella can survive for months in faeces and even years in dried on faeces.
Salmonella Risk Factors To Cattle
There are various factors that increase the susceptibility of your cattle to salmonella and many other diseases too.
Risk factors include:
- Age of cattle exposed (birth to two weeks old is a high risk period)
- Infection pressure
- Cow immunity and concurrent infections e.g. BVD
- Host Factors (a healthy gut is much less likely to become infected)
The main and most well know clinical sign of Salmonella Dublin is abortion.
However there are a wide range of signs that could indicate salmonella that also vary depending on age of cattle. Once the bacteria is established, diarrhoea is the main presenting sign but you may also see:
- Neurological signs
- Poor growth
- Sloughing of extremities (ears/ hooves)
- And many none specific signs e.g. high temperature, depression and recumbency
Animals that become infected and fail to fully clear the infection become carriers. It is these carrier animals that cause a salmonella outbreak to become endemic within the herd.
Latent carriers shed salmonella in low numbers and may only shed at times of stress (such as calving).
Passive carriers will only shed if the source is present.
Active carriers are the big problem, these animals will harbour the infection, multiply and shed in large quantities.
When animals are showing clinical signs (and have not been treated with antibiotics) it is most effective to try and detect the bacteria. This can be done by:
- Faecal Culture
- Post Mortem Examination
Herd Level Diagnostics
- Bulk Tank Serology
- Faecal cultures of animals with clinical signs
- Serology (blood sample) of calves
Response to treatment of Salmonella Dublin is generally poor if seeing severe clinical signs but it is susceptible to most broad- spectrum antibiotics. Vaccination with Bovivac S is particularly useful in the face of an outbreak.