Dairy calf respiratory disease most commonly occurs between 2 to 6 months of age, although it can occur earlier. The National Animal Health Monitoring System’s Dairy 2007 study indicates that 12.4 percent of preweaned heifers have respiratory disease, and of those preweaned calves dying, 22.5 percent were from respiratory disease.
The most common viral respiratory pathogens in dairy calves are BRSV and PI3, and the most common bacterial respiratory pathogens in dairy calves are Pasteurella bovis, Mycoplasma bovis, and Mycoplasma dispar, says Amelia Woolums, DVM, MVSc, Dipl. ACVIM, Dipl. ACVM, University of Georgia. While Mannheimia haemolytica can cause respiratory disease in dairy calves, it is not commonly found. “From the few reports available, it appears that M. haemolytica may be more commonly associated with respiratory disease in beef calves than in dairy calves,” she says.