RESUMEN
A Japanese Black calf became dehydrated on the first day of life and died on the third day. Gross examination revealed a large amount of yellowish-brown serous fluid in the abdominal cavity and whitish-yellow fibrin in the serosa of the abdominal organs. Patchy red spots were observed throughout the peritoneum, and the outer membrane of the umbilical arteries was dark red. Bacteriologically, Mannheimia haemolytica serotype 2 was isolated from the umbilical arteries and vein, liver, and kidney. Histopathology revealed inflammation with M. haemolytica serotype 2 in the outer membrane of the umbilical arteries and in the serosa of the bladder and intestinal tract. This is the first case of bovine peritonitis with histopathologic and immunohistochemical identification of M. haemolytica.