If you could do one thing to minimize an outbreak of salmonella, keep fresh cows away from sick, treated and lame cows. Co-mingling fresh cows with these animals is the single biggest risk factor for salmonella, says Sheila McGuirk, veterinarian at the University of Wisconsin’s School of Veterinary Medicine. When infected, sick and lame animals shed more salmonella organisms than any other group of animals on a dairy.