Pasteur’s work on fermentations has variously influenced the conception that veterinarians had of the origin of virulent diseases. Jean-Baptiste Chauveau asserted as early as 1866 the specificity of contagious diseases and their exogenous origin. Henri Bouley was initially a supporter of the spontaneity of these diseases. He became an advocate of the germ theory when Pasteur unambiguously demonstrated the causal role of anthrax bacteridia in 1877. Pasteur then had a fruitful collaboration with veterinarians during his work on chicken cholera, swine erysipelas , contagious pleuropneumonia and rabies. After Pasteur’s experience at Pouilly-le-Fort, Henri Bouley and Edmond Nocard, a disciple of Pasteur, were strong advocates for the adoption of vaccinations by veterinarians and farmers. Nocard’s work on various contagious animal diseases greatly contributed to the foundation of veterinary microbiology.