The infection by the Mycobacterium genus is important in pig farming due to the economic losses caused by total or partial carcass condemnation in slaughterhouses. The present study investigated the occurrence of a tuberculosis outbreak in pigs, based on the identification of lesions at the slaughter line of a slaughterhouse. At the inspection line of the slaughterhouse, carcasses were identified with viscera containing macroscopic lesions that indicated tuberculosis (granulomatous lymphadenitis). Tracheobronchial, mesenteric, and submandibular lymph nodes were collected, as well as liver samples and their corresponding lymph nodes. The samples were sent to the Federal Agricultural Defense Laboratory (LFDA/RS) and processed for the diagnosis of tuberculosis and the molecular characterization of Mycobacterium bovis. Based on the results of post-mortem and laboratory inspections, the occurrence was characterized as a tuberculosis outbreak in pigs, which originated from a farm in the state of Rio Grande do Sul, Brazil. Over three months, three batches, adding up to 2884 animals, were sent to slaughter, of which 102 (3.5%) had tuberculosis-like lesions at the inspection line. Based on these results, the productive process was investigated, assessing the feeding, water supply, and milk whey offered in the diet of pigs. It was concluded that the outbreak was caused by feeding unpasteurized or inadequately pasteurized (insufficient time x temperature relation) whey to the pigs. The use of whey from cheese production is a frequent practice in the state of Rio Grande do Sul and one of the risk factors for granulomatous lymphadenitis in pigs.