If a calf has become infected with salmonella, she’ll let you know. “Calves will broadcast when they are going to break with diarrhea,” says Sheila McGuirk, veterinarian at the University of Wisconsin’s School of Veterinary Medicine. Roughly 12 to 24 hours before diarrhea begins, a calf’s temperature with rise 1.5 to 2 degrees Fahrenheit. That’s the time to start antibiotics, McGuirk says. Work with your veterinarian to determine which antibiotic will be most effective.