Salmonella Prevalence on Dairy Herds Studied

A Cornell University study sheds light on the risk of clinical salmonellosis in northeast dairy herds. The study, directed by Lorin Warnick, veterinarian and epidemiologist at Cornell University, followed over 325,000 female dairy cattle for at least a year.

Last week, Daryl Nydam, veterinarian and epidemiologist at Cornell, shared highlights of the study at two, one-day calf workshops offered by the Professional Dairy Producers of Wisconsin.

During the study, participating veterinarians submitted manure samples from cows, heifers and calves displaying clinical symptoms of the disease. Among the calves, culture results showed 18 percent of 834 manure samples tested were positive.

Results also show the incidence was highest in pre-weaned calves compared to weaned heifers and mature cows. The incidence rate, or number of cases per 1,000 animal-years, was 7.7 cases. “So, if you had 1,000 head of calves, you’d expect about eight clinical cases of salmonellosis in a year,” Nydam said. Although the overall incidence was low, some herds experienced severe outbreaks with high death loss among affected calves.

A follow-up study at Cornell University examined how long infected animals shed Salmonella into the environment. “Only 5 percent of the calves had observed shedding for more than 30 days,” Nydam said. Cows appear to shed the organism longer. In the study, 30 percent of the cows shed for more than a month after they had recovered, Nydam says.

“Salmonellosis can be a dose-dependent infection, so shovel stuff up,” Nydam stressed to workshop participants at the Madison, Wis., location. “Keep the dose in the environment as low as possible.” It also is a good reminder to isolate calves from older animals.