This study was carried out for an external R&D service for a pharmaceutical laboratory. The objective was twofold. First, for our client, this study made it possible to compare the effectiveness of two of these vaccines for the prevention of enzootic pneumonia in breeding based on clinical criteria, technical performance (ADG, mortality) and injury criteria. at the slaughterhouse. This study also made it possible to study the dynamics of Mycoplasma hyopneumoniae in breeding by comparing the number of positive pigs (by PCR and by serological analysis) and the bacterial load between vaccinated pigs with unvaccinated pigs raised together.