Salmonella infection is one of the most well-known diseases affecting cattle in Ireland. Samonella infections is a serious drain on the profitability and productivity of the Irish dairy herd. In addition, there is the added risk of being a zoonotic disease, meaning infection can be transmitted to humans from animals. Infection in the dairy herd has the potential to cost up to €112 per cow, per year. Research has shown that herds which include vaccination as part of a control plan record superior profits in comparison to unvaccinated, positive herds to a value of €11,800 based on a 100-cow herd.
Salmonella is considered endemic in Ireland and can be commonly found in herds throughout the country. The majority of salmonella infections in Irish cattle are caused by one of the following serotypes: Salmonella typhimurium or Salmonella dublin, with abortion outbreaks typically associated with Salmonella dublin. Other clinical signs such as pneumonia, meningitis, arthritis, osteomyelitis and sloughing of extremities are also seen. Salmonella is primarily shed in the dung of infected cattle and infection is usually picked up by oral ingestion. Once an animal is infected, they can become carriers of the infection for life. This is known as latency and it is an important component in maintaining infection within a herd. Carrier cattle will often shed the bacteria during times of stress such as around calving or changes in management, acting as a source of infection to the rest of the herd. As many dairy herds have expanded in recent years, there has been a heightened risk of introduction of the disease through the buying-in of these carrier animals.
As with any disease outbreak it is important to involve your attending veterinary practitioner to assist with diagnosing the exact cause of disease and to formulate an effective control plan. Diagnosis of infection by post mortem investigation is considered gold standard. Any aborted foetuses should go to the local regional veterinary laboratory as soon as possible. In a scour outbreak, multiple dung samples can be used to help identify bacteria while paired blood samples can be taken can be taken to demonstrate a rising level of immunity to the infection. The first sample is taken during the active phase of infection while the second sample is taken four weeks later.
Bulk milk antibody testing can be a useful surveillance tool for dairy herds too. Although results might not indicate active infection within herd at the time of sampling, monitoring results can give an idea of the level of exposure within the herd and potential trends of infection. Recent research has shown exposure of Irish dairy herds to salmonella is very common, with 49% of bulk milk tanks testing positive for salmonella antibodies, indicating cattle in these herds had come into contact with the bacteria at some point in the preceding months.
As the disease is notoriously difficult to eliminate from farms, vaccination and strict management measures must be implemented to reduce the spread of infection. These can include –
- Maintaining a closed herd/purchase from herds of known disease status – If buying in, quarantine arrivals for a period of 4 weeks minimum.
- Strict biosecurity – Cows which have aborted should be isolated for one month and any abortion materials should be disposed of in a hygienic manner. Ensure fencing is stock proof to avoid break-in infection from neighbouring herds.
- Management of slurry – Salmonella bacteria can survive for prolonged periods in slurry tanks and for up to 300 days on soil. Faecal material from clinical cases must be prevented from entering the slurry tank.
- Strict hygiene – A disinfection point should be in place for everyone who enters and leaves farm to use. Hygiene of buildings between batches of animals is critical while personal hygiene should also be maintained as a result of the zoonotic risk.
- Rodent and bird control – As pests can spread disease, a plan should be in place for rigorous control, especially with regard to access to feed stores.
Bovivac S is the only vaccine available for Salmonella dublin and Salmonella typhimurium in Ireland. For best herd control of salmonellosis, it is advisable to vaccinate all animals in the herd. Healthy calves from approximately three weeks of age can receive the primary vaccination course of two 2ml injections separated by an interval of 14-21 days. Calves over six months of age and adult cattle should receive two 5ml injections 21 days apart. Depending on the level of infection circulating in the herd, one annual vaccination should maintain a sufficient level of immunity in the herd. Although not licensed for the control of abortion, research has reported that the proportion of Salmonella dublin positive abortions from vaccinated herds was significantly lower than in herds which were not vaccinating. To determine the most appropriate time to vaccinate your herd, please consult with your attending veterinary practitioner.
In conclusion, the implications of a salmonella outbreak can be severe and result in significant financial, production and welfare costs. Not to mention the stress of its potential zoonotic risk. Vaccination can form the cornerstone of control along with good management, strict hygiene protocols and high biosecurity standards.