| Swine production systems and the way in which pig are raised, have experienced many changes in the last decade, moving from extensive production to a more intensive one. This transformation has changed the presentation and epidemiology some diseases. Despite all these changes, respiratory problems still play a major role in this industry. Mycoplasma (M.) hyopneumoniae, which has a worldwide distribution, is considered one of the most important respiratory pathogens in pigs.; Since present knowledge on M. hyopneumoniae is derived from the old traditional continuous flow production system, several experiments were therefore performed to have a better understanding of M. hyopneumoniae shedding and transmission under experimental and modern farm conditions. These experiments also attempted to understand the effect of vaccination against M. hyopneumoniae on its shedding and prevalence in the swine populations raised using modern production methods.; Results of the studies presented in this thesis show that M. hyopneumoniae shedding and transmission is a complex process. In experimental settings, the microorganism was detected in nasal swabs tested by nested polymerase chain reaction (N-PCR) only for a short period post infection. There were also some differences in shedding patterns depending on pig origin. Under field conditions, the majority of the pigs were positive one time, with the timing of infection apparently related to prevalence at weaning, thus demonstrating the dynamics of this infection.; The use of M. hyopneumoniae vaccination showed that over 80% of the vaccinated sows seroconverted and that these antibodies were transferred to their piglets via colostrum. Sow vaccination against M. hyopneumoniae reduced piglet prevalence at weaning and could therefore be used as a tool to control M. hyopneumoniae in modern swine farms.; Similar results were observed in vaccinated pigs, although pigs that received the one dose commercial vaccine seroconverted later as compared to pigs receiving two doses of the commercial vaccine. Pig vaccination reduced M. hyopneumoniae prevalence during both nursery and finishing periods, where most of the positive pigs tested by N-PCR were positive just once and the cumulative probability of no infection showed a clear reduction in the vaccinated groups. |
