Pathology of peritonitis in cattle.

Although peritonitis is highly prevalent in cattle, there have been only limited studies on the pathology of this condition. We describe the gross and histological aspects of primary and secondary peritonitis in cattle based on necropsy reports of 46 cases. Twenty-six were female (26/46; 56.5%) and 24 male (24/46; 43.5%), 31 (31/46; 67.4%) beef breed and 15 (15/46; 32.6%) dairy breed. Twenty were 0-12 months old (20/46; 43.5%), nine were 13-36 months old (9/46; 19.6%) and 15 were >36 months old (15/46; 32.6%). Two were of unknown age. Primary peritoneal tuberculosis (PT) was present in 7/46 cases (15.2%) and macroscopic lesions were mainly multifocal (6/7; 85.7%) and characterized by white to yellow, firm nodules of variable size. Histologically, they were characterized by granulomatous inflammation with intralesional acid-alcohol-resistant bacilli. All cases were positive for Mycobacterium tuberculosis complex and negative for Mycobacterium avium on immunohistochemistry. Secondary peritonitis was diagnosed in 39/46 cases (84.8%), caused by organ rupture or perforated ulcer (21/39; 53.9%), traumatic reticuloperitonitis (9/39; 23.1%), post-castration inflammation (7/39; 17.9%) or omphalophlebitis (2/39; 5.1%). Macroscopic lesions in secondary peritonitis were mainly diffuse (31/39; 79.5%) and comprised roughening of the peritoneal surface, which was covered by free white to yellow-orange fibrin strands with a liquid to pasty, opaque, white-grey effusion (30/39; 76.9%). Bacteriological culture of the exudate from 15 secondary peritonitis cases identified mainly Truperella pyogenes (8/15; 53.3%) and Escherichia coli (5/15; 33.3%). This study enhances our understanding of the pathological manifestations of peritonitis in cattle.