Hemorrhagic bowel syndrome (HBS) is an acute condition that occurs in adult cattle, primarily dairy cows. It usually affects an individual animal, but outbreaks can also occur. Despite treatment, the mortality rate can exceed 85% (Elhanafy et al., 2013). The disease is more common on larger farms (>100 animals), in animals with high milk production, early in lactation, and typically from the second or later lactation. High-energy diets combined with low fiber content and feed changes are considered risk factors, although there is no strong epidemiological or experimental evidence for this (Kirkpatrick & Timms, 2004; Berghaus et al., 2005). The animals exhibit sudden depression, anorexia, and a decrease in milk production. Clinical examination reveals signs of shock (tachycardia, pale mucous membranes, hypothermia), often an audible abdominal ping, melena, and ileus. Without treatment, there is rapid progression and death. These animals are sometimes found dead without observed symptoms (Elhanafy et al., 2013; Desrochers & Anderson, 2016). HBS is characterized by one or more intramural hematomas in the small intestine. This results in intestinal obstruction, ileus, and intestinal bleeding (Desrochers & Anderson, 2016). It is doubtful whether the acute intestinal obstruction and bleeding alone can explain the rapid deterioration of these animals, suggesting additional toxemia might be involved.

The cause of HBS is still unknown. The purpose of this project is to identify risk factors contributing to this condition and to further characterize the lesions in affected animals both macroscopically and histologically.