doi:10.1177/03009858241235393engPérez, EstelaUzal, Francisco A.de Miguel, RicardoRodríguez-Largo, AnaReséndiz, RaúlStreitenberger, NicolásMacías-Rioseco, MelissaGómez, ÁlexCalvo-Sánchez, NataliaPérez, MartaLuján, LluísAsín, JavierMannheimia haemolytica associated fibrinonecrotizing abomasitis in lambsART-2024-137877Mannheimia haemolytica–associated abomasitis has been clinically described as a cause of sudden death in lambs, but it is poorly characterized. We describe the pathological features of a severe fibrinonecrotizing abomasitis in 3 lambs that died suddenly. All 3 abomasums had a thickened submucosa due to edema and necrotic areas delimited by bands of degenerate neutrophils with slender nuclei (oat cells) and angiocentric distributions. The overlying mucosa was congested. Myriads of gram-negative coccobacilli were observed within the oat cell bands. M. haemolytica was isolated from the abomasum in all 3 animals and was serotyped as A2 in one of them. Pericarditis and pleuritis were observed in 2 of the lambs. Clostridium spp. were isolated in 1 lamb and detected by immunohistochemistry in the 3 animals, suggesting clostridial co-infection. M. haemolytica should be considered among the differential diagnoses of necrotizing abomasitis in lambs.2024http://zaguan.unizar.es/record/13310310.1177/03009858241235393http://zaguan.unizar.es/record/133103oai:zaguan.unizar.es:133103Veterinary Pathology 61, 4 (2024), 604-608byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess