CHALLENGE EXPOSURE OF CATTLE VACCINATED WITH A CHEMICALLY ALTERED STRAIN OF PASTEURELLA-HAEMOLYTICA

Abstract

Calves vaccinated with a chemically altered strain of P. haemolytica and nonvaccinated controls were challenge exposed intranasally with the Cooper strain of infectious bovine rhinotracheitis virus. Five days later, the calves were challenge exposed intratracheally with P. haemolytica type A1. Calves that had been vaccinated with large, medium or small doses of the chemically altered vaccinal strain of P. haemolytica had various degrees of resistance to the experimental challenge exposure. Nonvaccinated animals developed severe respiratory tract disease and pneumonia after challenge exposure.