Probable role of viruses in calfhood diseases.

Bovine enteroviruses, bovine viral diarrhea virus, rotavirus (formerly called reovirus-like agent), coronavirus-like agent, bovine adenovirus, and bovine parainfluenza-3 virus have been isolated from calves suffering from neonatal disease. The experimental disease produced by these viruses is not necessarily severe or fatal, but under farm and ranch conditions, each probably serves as an added to mortality from neonatal disease. After initial losses following the introduction of a virus into a herd, the subsequent losses will be limited because the cow will produce antibodies to protect the fetus during gestation. Antibodies will also be concentrated in colostrum to protect the calf at birth. However, colostrum must be fed immediately after birth, before the calf becomes infected.