Enzootic pneumonia is a major health and economic issue in a number of French farms, despite the widespread use of vaccination. To assess the efficacy of a control program, vet practitioner can use different diagnostic methods like observation of clinical symptoms, lung lesion scoring at slaughter and laboratory tests. On a 200-sow farrow-to-finish farm with important respiratory signs caused by Mycoplasma hyopneumoniae, a medication protocol has been implemented on two batches,. The treated batches were compared to two non-treated control batches regarding infection dynamic of M. hyopneumoniae. In the four batches, we performed clinical evaluation, serological screening and lung examination at slaugther.

The pigs from the treated batches have developed disease later than the control pigs, seroprevalence to M. hyopneumoniae was lower among finishers from treated batches than those from control batches. However, lung scoring showed statistical differences between the treated and untreated batches with more lesions in pigs from the treated batches and more lungs with scarre tissue in pigs from the untreated batches. These results question about interpretation of lung lesions scoring diagnosis method.