Vet. Path. 11: 535-547 (1974)

Abstract. The gross abnormalities in the intestines of 10 horses with a history ofchronic weight loss varied greatly. The principal microscopic change was granulomatous in-flammation characterized by lymphocytes, plasma cells, macrophages, epithelioid cells and giant cells. Mycobacferium tuberculosis, avian type, was isolated from the gut content of one horse, but no cause was found in the others. Horses previously reported to have tuberculosis had lesions similar to those described here. These lesions are also similar to those in Crohn’s disease of man. Although chronic wasting in the horse secondary to many disease pro-cesses is well known, there are no reports of wasting caused by granulo-matous enteritis. There is also little information on chronic diarrhea in the horse [8, 101. This paper discusses 10 horses that had wasting associated with diffuse granulomatous enteritis. The gross and microscopic changes in the gut and other organs are described, and they are compared to those in Crohn’s disease and tuberculosis. Materials and Methods Ten horses with a history of weight loss for at least 3 months were examined at the New Bolton Center clinic in a 2-year period. All but one were Standardbreds and were 2-1 1 years old. There was either no history of diarrhea or one of intermittent diarrhea with semi-formed feces. All the horses were thin and hypoalbuminemic with various amounts of y-globulin and total protein (table I). Cytological evaluation of peritoneal fluid showed little or no phagocytic activity of peritoneal mesothelial cells. In one horse Mycobacterium tuber-culosis, avian type, was isolated from the feces