Keep an Eye Out for Salmonella

July 5, 2009 07:00 PM

Travis Thayer, DVM, AgriLabs Technical Services

As summer heats up, environmental conditions are perfect for the growth of disease causing bacteria. Good environmental conditions for bacteria, combined with cows and calves having weakened immune systems due to heat stress, increase the risk of Salmonella infection. Salmonella can affect cows of all ages and production classes, often resulting in devastating losses to a dairy. Now is as important as ever to stay vigilant for signs of this disease.

The route of infection in all cattle, regardless of age, is fecal-oral transmission - the cow or calf ingests fecal contaminated food or water, or comes into contact with contaminated equipment, such as drench guns, stomach tubes, etc. In adult dairy cows, the typical clinical picture of Salmonella infection is severe, often bloody, foul smelling diarrhea with a high fever.  In addition to blood, one may also observe yellow "chunks” in the feces, from an inflammatory protein in the intestines called fibrin. Depending on the type of Salmonella organism present, and the severity of infection when caught, antibiotic therapy may not be very effective, and many animals either die as a direct result of infection or never return to adequate milk production and are culled. In severe cases, Salmonella may kill a cow so quickly that she dies before any clinical signs of diarrhea.

Salmonella often affects calves in a similar manner as adult cows - most commonly in the first couple weeks of life, as severe, often bloody, scours with a high f ever. However, Salmonella can sometimes be present in calves in a couple of different forms, as well. In very young calves, Salmonella can cause septicemia (blood infection) which is characterized by high fever, severe depression, and often death. Salmonella can also affect older calves, often around the time calves are moved from hutches to group pens. Signs of infection in these older calves may often include symptoms of pneumonia with or without classic signs of diarrhea and high fever.

Treatment of Salmonella includes antibiotic therapy combined with supportive care, including electrolyte and fluid replacement, and fever reducers. However, many types of Salmonella are highly resistant to antibiotics, and treatment may or may not be effective. Your veterinarian will likely recommend a Salmonella culture with antibiotic sensitivity testing to help choose the most appropriate antibiotic therapy for that particular strain.  

Since treatment for Salmonella infection often yields poor results, the best way to control Salmonella on the dairy is prevention. While Salmonella is present in the environment in most dairies, whether a cow gets it or not is based on the resistance of the animal (which is lowered in times of stress) and the overall dose of Salmonella organisms. While sometimes weather and other conditions cause stress beyond our control, good nutrition and management for cow comfort help to minimize stress on cows. There are also a number of nutritional products that have been shown to decrease Salmonella infection in cows. Good sanitation and biosecurity protocols help to minimize the amount of Salmonella organisms animals are exposed to. 

Vaccination against Salmonella has not been very effective in the past. However, recently, new vaccine technology (SRP® Technology) has been developed which builds immunity against a wide variety of Salmonella organisms. In addition to protection against clinical illness, this novel vaccine technology also decreases the amount of Salmonella organisms shed in the manure, which in turn decreases the exposure level of other animals on the farm.  

The best source of information on Salmonella treatment and prevention is your veterinarian.  Talk with him or her about your specific risk for Salmonella infection on the farm, what prevention and treatment practices are most important for your dairy, and how best to implement them.  Additional information about vaccination for Salmonella can be found at

Travis Thayer obtained a bachelor of science degree in microbiology and a DVM degree from the University of California-Davis. He then practiced dairy production medicine in the Central Valley of California and joined the AgriLabs technical services group in June 2005. You can e-mail him at

This column is part of the Dairy Today eUpdate newsletter, which is delivered to subscribers biweekly and includes dairy industry analysis, dairy nutrition information as well as the latest dairy headline news. Click here to subscribe.



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