Salmonella infections can strike cattle during every season, particularly during warm weather, when growth conditions for Salmonella bacteria are ideal, say Travis Thayer, DVM, AgriLabs. With a doubling time of about 20 minutes, even a small amount of initial contamination of feed, water, or general environmental areas around the farm can result in a large bacterial exposure. Salmonella infects cattle and other animals through oral ingestion. Prevention revolves around decreasing the amount of bacteria in the environment while increasing animal resistance to the disease.
Salmonella bacteria are widespread in the environment and can be found on many dairies. The presence of Salmonella alone does not guarantee that animals will get clinically ill from exposure, but it certainly represents a risk that a future problem could occur.
According to information from Washington State University College of Veterinary Medicine, clinical illness from Salmonella is a function of three main factors:
- Susceptibility of the exposed animal: Animals that are stressed from other factors (such as parturition, nutritional disruption, extreme heat or cold, other inclement weather, shipping, etc.) have lowered immune responses, and are susceptible to a bacterial challenge that otherwise may not make them sick.
- Infectious dose of the organism: As with any infectious disease, the more organisms an animal is exposed to, the more likely they will become sick.
- Virulence of the particular serotype of Salmonella involved: While many researchers feel that all serotypes of Salmonella enterica have the potential to cause disease under the right conditions, certain serotypes of Salmonella are much more virulent than others, and the presence of an extremely virulent organism, even in small numbers, represents a much higher risk than the presence of a less virulent strain.
Here are a few general suggestions to reduce your clients’ risk of Salmonella infection on the dairy:
Minimize stress on animals
Obviously, some environmental factors, such as weather, are beyond our control, but we can take steps to make cows as comfortable and stress free as possible – focus on cow comfort, calm and quiet cattle handling, solid nutritional programs, etc.
Practice good biosecurity and sanitation protocols.
- Isolate sick animals from healthy ones – do not house sick animals in the calving pen.
- Isolate all animals with diarrhea until infectious diseases like Salmonella have been ruled out or appropriately treated.
- Do not push up feed with the same equipment that is used to carry dead animals or scrape manure alleys.
- Sanitize all equipment used to treat sick animals before next use.
- Avoid contamination of feed and water sources with manure.
Vaccinate animals to increase resistance against Salmonella
There are several vaccine products available for Salmonella infection in cattle. Products vary widely in efficacy and breadth of coverage, and include whole cell bacterins, core antigen bacterins, and subunit vaccines. One type of subunit vaccine, which uses specialized proteins on the surface of the bacteria (siderophores and porins), not only protects against disease caused by multiple strains of Salmonella, but decreases fecal shedding, resulting in less bacteria excreted into the environment, and thus less exposure for cows in that herd.
Salmonella infection on the dairy is not only economically devastating to farms – it represents a public health risk for people handling the animals and their families. Control requires comprehensive management steps to decrease exposure and optimize animal resistance to infection.