Malabsorption is the impaired uptake of one or more nutrients from the intestinal lumen into the body’s systemic circulation despite adequate dietary intake, resulting in nutritional deficiency, weight loss, and secondary clinical signs that reflect the specific nutrients failing to be absorbed. In horses, malabsorption can affect simple sugars (glucose), proteins (amino acids), fats, fat-soluble vitamins, and minerals, and may result from disease of the small intestine — where most nutrient absorption occurs — or from diffuse infiltration of the intestinal wall that reduces functional absorptive surface area.
The clinical presentation depends on the degree and duration of the disorder. Weight loss despite an adequate ration is the most consistent sign; a horse that is fed appropriately but fails to maintain condition despite dental health and parasite control should prompt investigation of intestinal absorptive function. Protein malabsorption leads to hypoproteinemia, with low serum albumin causing ventral edema (kept fluid in the belly and lower limbs). Fat malabsorption produces pale, malodorous, voluminous feces and fat-soluble vitamin deficiencies over time. loose stool accompanying absorptive failure often accompanies malabsorption but is not invariably present.
Diagnosis relies on oral glucose absorption or D-xylose absorption tests: a baseline blood sample is taken, glucose or xylose is administered orally at a measured dose, and blood glucose or xylose concentrations are measured at timed intervals. A blunted or flat absorption curve indicates small intestinal dysfunction. Conditions underlying equine malabsorption include inflammatory bowel disease (granulomatous enteritis, lymphocytic-plasmacytic enterocolitis), alimentary lymphoma, widespread small intestinal lesions from migrating parasitic larvae, and intestinal lymphangiectasia. Treatment is directed at the underlying cause where possible; supportive management includes highly digestible feed, parenteral nutrition in severe acute cases, and corticosteroid therapy for inflammatory conditions. Regular monitoring weight loss over treatment is essential to monitor treatment response.