Hemorrhagic bowel syndrome affects rapidly growing swine 4–6 mo old. Pigs die suddenly without evidence of diarrhea, but the small intestine is thin-walled on necropsy and filled with either clotted or unclotted blood. The large intestine usually contains tarry fecal material but no lesions suggestive of swine dysentery, salmonellosis, proliferative enteritis, or intestinal spirochetosis. The condition can be prevented by the administration of either bacitracin or chlortetracycline in the feed. When performing a necropsy, the mesenteric root should be palpated before opening the abdomen. A peracute form of proliferative enteritis may have similar clinical and gross lesions; however, histology and culture of the intestine will discern the presence or absence of epithelial proliferation and Lawsonia intracellularis.
The cause in most cases is believed due to intestinal volvulus. Predisposing factors may include vigorous exercise, handling, fighting, piling, or irregular feeding. Long-loined pigs may be more likely to develop mesenteric torsion than shorter pigs. Rotation of the entire intestine, including the posterior part of the duodenum and the anterior part of the rectum, around the root of the mesentery obstructs venous outflow of blood, which causes blood to pool and stagnate in the intestine and soon results in infarction. Rotation may be only partial and difficult to demonstrate at necropsy, which makes diagnosis more challenging.