While Salmonella is a major concern for dairies across the country, it is especially challenging for Western and Southern operations, where the warmth-loving bacteria can grow.
“Salmonella numbers can double every 20 minutes in warm, moist feed,” says Bradford Smith, DVM, DAVIM, professor emeritus in the School of Veterinary Medicine at the University of California-Davis. “It doesn’t take long for the bacterial load to overwhelm the animals that consume contaminated feed and cause clinical infections.”
Freezing kills some of the bacteria and reduces numbers, but some strains of Salmonella can survive for long periods in manure, slurry and soil if it doesn’t freeze. Thus, it lies in wait for an opportunity to grow in hot weather.
While little research has been done to evaluate the regional incidence of Salmonella on dairies, it appears that dairies in warmer climates are more widely affected. Smith theorizes that this is due to a number of factors, including:
- Hot weather causing cows to go off feed, which can lead to stale feed sitting in warm conditions, the perfect growth opportunity for Salmonella. Digestive upsets from spoiled feed also can leave cows more susceptible to Salmonella infections.
- No “big freeze” meaning the bacteria can perpetually survive in the environment without a killing frost to reduce numbers.
- Greater concentration of animals on large dairies, which may increase environmental exposure of animals to manure — one of the primary transmitters of Salmonella from animal to animal.
- Commodity-based diets that are not ensiled, which are often fed in the West. Silage-based diets often fed in the Midwest and the Northeast pose a lower risk because the low pH of ensiling corn (but not haylage) also kills the bacteria.
Smith cautions, however, that dairies in the Midwest and Northeast are not immune to the challenges of Salmonella. The advent of large manure slurry storage systems that never completely freeze over may be one reason why Salmonella is hitting these regions hard as well, and spells of hot weather, which occur in almost all parts of the United States.
“Any heat-abatement measures we can take to make cows more comfortable — including shade, misters and fans — will help in the battle against Salmonella,” Smith says. “It’s important to keep cows, especially fresh cows, on a consistent plane of eating fresh feed, regardless of where they live.”
For more information on strategies for helping control Salmonella, talk to your herd veterinarian.
Source: Pfizer Animal Health