Pathomorphological Characteristics of Respiratory Infections in Pigs from Different Production Categories and at the Slaughter Line

Abstract In the complex conditions of intensive pig breeding, respiratory diseases remain a significant health and economic challenge, despite substantial progress in diagnostics and control measures. This study analyzes the pathoanatomical and histopathological changes in the respiratory organs of dead pigs from different production categories, as well as in clinically healthy fattening pigs inspected on the slaughter line. The research was conducted on a farrow-to-finish pig farm in southern Serbia without immunoprophylaxis against respiratory infections. A total of 182 animals were examined: 50 suckling piglets, 50 weaned pigs, 30 pre-fattening pigs, and 52 fattening pigs. Macroscopic and microscopic analysis of lungs, trachea, tonsils, and tracheobronchial lymph nodes revealed interstitial pneumonia predominated in young pigs categories (suckling and weaned), while older pigs (pre-fattening) showed purulent, fibrinous, and mixed broncho-interstitial pneumonia, often with pleural adhesions. Among fattening pigs, 82.7% showed no macroscopic lung changes. In cases of interstitial pneumonia, histology revealed type II pneumocyte hyperplasia, fibrosis, and inflammatory cell accumulation in the interstitium. Purulent bronchopneumonia exhibited neutrophilic granulocytes and epithelial desquamation, while fibrinous bronchopneumonia showed extensive fibrin deposits. Catarrhal inflammation of the trachea was most common in weaned pigs (38.0%), while tonsillitis occurred most frequently in suckling piglets (24.0%) and weaned pigs (28.0%). Reactive lymphadenitis in the tracheobronchial lymph nodes was highest in pre-fattening pigs (63.3%), suckling piglets (44.0%) and weaned pigs (40.0%). Although pathomorphological findings alone cannot confirm an etiological diagnosis, they guide further diagnostic investigations and emphasize the need for improved control, prevention, and diagnostic programs for respiratory infections in pigs.