Russ Daly, DVM, Dipl. ACVPM, knows firsthand the difficulties associated with diagnosing and dealing with Salmonella spp. as a causative agent of clinical illness in beef herds. In a 2008 Journal of the American Veterinary Medical Association paper, Daly, of South Dakota State University, outlines a 2006 case in which three separate groups of cows and calves on a South Dakota cow-calf operation were infected with Salmonella enterica serotype Newport.
The cows were calving in February and a strong blizzard arrived with severe wind chills and heavy snow for two days. In the hardest hit group, S. Newport was recovered from cows and calves experiencing clinical illness ranging from severe watery and bloody diarrhea, dehydration, weakness and death. Cow mortality was 7.9% and calf mortality was 14.4%, despite supportive and antimicrobial treatment. Ear-notch samples indicated a 2.7% bovine viral diarrhea virus (BVDV) persistent-infection rate in calves born within the S. Newport group.
“Traditionally, S. Dublin is the serotype most often associated with disease in dairy and beef cattle, as it seems to be more host-adapted for cattle,” Daly notes. From 2007-2011, S. Dublin has been the most common serotype isolated from beef and dairy cattle at SDSU. “Prior to that, we had been seeing more Newport than Dublin coming through the diagnostic lab. Typhimurium is the next most common serotype diagnosed in sick cattle here, but in much fewer cases compared to Dublin.”
A fast-moving Salmonella spp. can sicken and kill beef cows and calves. Daly says surveys of normal cattle and their environments find many different serotypes isolated, however those serotypes identified are not often associated with disease outbreaks. “In one survey, 8.5% of beef cattle operations had Salmonella spp. in their environments; 3% of beef cattle at slaughter; 3% and 5% in feedlot cattle before and after slaughter. The National Animal Health Monitoring System 2007-08 study found 9.2% of beef herds positive in at least one animal and 0.5% of animals overall. These are decreases from the previous study 10 years prior, with at least 20 different serotypes represented.”
Clinical signs of salmonellosis
In a clinical salmonellosis outbreak, cows may present with profuse watery diarrhea, sometimes bloodtinged, with high fevers, inappetence, weakness and incoordination leading to dehydration and death. In some cases there can be abortions in pregnant cows.
Salmonellosis will create clinical signs in calves in the same manner as described in the cows, but in the throes of the outbreak, young calves might die shortly after birth, Daly says. “In our case, we cultured S. Newport out of a calf that had died at 24 hours of age. When the cow herd is affected, a lot of calves might just show the secondary effects of starvation.”