Salmonellosis (often referred to as salmonella) is not usually a concern for most beef producers. Typically, dairies will be more likely to find incidences of salmonella spreading throughout their herd as a result of their confined operations. However, it is not impossible for beef cattle, particularly young calves, to become stricken with salmonella. Fall-calving herds face a timely threat as salmonella tends to peak in the summertime.
Dr. Gaby Maier, assistant specialist in the University of California (UC) Davis cooperative extension, said the disease isn’t very common as it is. At UC Davis, all livestock that stay overnight are tested for salmonella, and in a set of sick cattle, a little over 2 percent have tested positive.
The USDA National Animal Health Monitoring System (NAHMS) conducted a study from 2007 to 2008 over beef cow-calf health and management systems. One objective of the study was to observe the occurrence of salmonella on beef cow-calf operations. Samples were taken from 173 operations across 24 states. Out of the operations sampled, about 1 percent of cattle tested positive for the disease.
It’s not a common disease, but it does happen.
Prevalence of salmonella varies seasonally, with a peak prevalence during the summer, according to UC Davis. Fecal salmonella shedding also varies, with post-partum cows shedding salmonella more frequently. This makes fall calves the perfect target for disease, especially because when salmonella does cause serious illness, it is usually in calves.
“It has to do with their immune system,” Maier said. “It’s still developing so they are much more susceptible to something in the environment.
Maier added that colostrum status also played a role in the disease’s development. Calves lacking sufficient amounts of colostrum are more predisposed to salmonella because their immune system is still very naïve to antibodies and needs to develop.
Salmonella Dublin is a particular strain of salmonellosis that is cattle host-adapted and has potential for establishing a carrier state in cattle after infection, as well as widespread infections at the herd level. Cornell University said the strain typically presents as a respiratory illness, primarily in animals less than 2 months of age.
Clinical symptoms include septicemia and terminal diarrhea. Stress can also result in clinical signs in infected carrier animals. Cornell recommends excellent nutrition and management, especially around post-calving.
Spread and treatment
Although it’s infrequent, salmonella can be passed onto humans, so practicing good hygiene and management is essential to avoid illness.
Cattle can become infected with the disease after ingesting feed or water that has been contaminated with feces from animals spreading the organism.
Cattle shedding the salmonella bacteria can often go unnoticed. It can be difficult to identify what cows are shedding the bacteria because subclinically affected cows can shed as many organisms in their manure as those sick with salmonella.
Similar to E. coli, animals can be shedding the disease but not infected, Maier told WLJ.
Salmonella can be transmitted by a variety of “different critters,” Maier said. This could include waterfowl, rodents, or dogs.
Fecal-oral transmission is the most common spread of the disease. Infection can also occur via saliva and nasal secretions, which would be easily spread at shared waterers.
Outbreaks typically last several months, according to the University of Wisconsin-Madison. This can be a result of a multitude of factors: persistence in the environment; prolonged shedding; or reinfection of susceptible animals.
“Treatment is often controversial,” Maier said. She recommends always consulting a vet for treatment options.
“You would follow pretty standard calf diarrhea protocol,” Maier said. “Administer fluid replacement in terms of oral fluids, or if the calf is too weak, IV fluids. If you suspect the calf to be septic or bacteremic, calves should also be on antibiotics.”
In terms of prevention, there have been few well-designed studies evaluating salmonella vaccines, and most are ambiguous in terms of efficacy. Vaccinations will not stop infection, but some vaccines may reduce the severity of infection and curtail the mortality rate.
Other management decisions to decrease the opportunity for salmonella is to maintain a closed herd, keep calving cows and sick cows separate, restrict access to feeding areas cohabitated with birds or waterfowl, and control rodent and feral animal populations.
Because many infected animals are subclinical, in an outbreak, handle all animals as if they were shedding. — Anna Miller, WLJ editor