Overview o Malassimilation Syndromes in Large Animals.doc

Overview of Malassimilation Syndromes in Large Animals Malassimilation is a defect in the ability of the GI tract to incorporate nutrients into the body either due to malabsorption or maldigestion. Malabsorption is the failure of passage of nutrients from the lumen of the bowel into the bloodstream, while maldigestion is the failure of intraluminal degradation of dietary constituents due to a defect in pancreatic exocrine function, bile acid content, or brush border enzymes. Maldigestion alone is an infrequent cause of malassimilation in large animals. Maldigestion syndromes are uncommon in horses compared with other domestic species. The equine pancreas secretes only low concentrations of digestive enzymes and probably plays a small role in nutrient digestion. Some disease processes involve both maldigestion and malabsorption, such as is seen in young animals with lactase deficiency. Diseases of malabsorption are much more common in horses than are diseases of maldigestion. Etiology and Pathogenesis Many diseases, by altering the normal absorptive mechanisms of the small intestine, induce a malabsorption syndrome. In horses, these include the following: 1) inflammatory or infiltrative disorders—diffuse lymphosarcoma of the small intestine (alimentary lymphoma); enteritis due to eosinophilic, lymphocytic-plasmacytic, or basophilic infiltrate; multisystemic eosinophilic epitheliotropic enterocolitis; granulomatous enteritis (inflammatory bowel disease); Lawsonia intracellularis (weanling foals, yearlings); intestinal ischemia and damage due to migration of Strongylus vulgaris larvae, small strongyles, or Strongyloides westeri (foals) infection; cryptosporidia; postinfarction inflammation; amyloid Aassociated gastroenteropathy; multiple abscessation in the bowel; tuberculosis; histoplasmosis; intestinal Rhodococcus equi infection; invasive enterocolitis (Salmonella spp); 2) biochemical or genetic abnormalities—congenital or acquired lactase deficiency (lactose intoler