Malabsorption occurs when the horse's digestive system cannot absorb nutrients from the digestive track: the intestinal wall is not functioning properly. Most often this dysfunction is caused by inflammation. Besides malabsorption, body fluids containing protein and other nutrients, may spill back into the gut lumen.The result is the horse's inability to maintain weight. Inflammatory Bowel Disease (IBD), Protein Losing Enteropathy (PLE), and the insuing malasorption are increasingly recognized as a cause of chronic weight loss in horses, sometimes without diarrhea or colic present. When the cause of the malabsorption is unknown it is referred to as Malabsorption Syndrome.

Malabsorption is usually suspected when chronic weight loss and poor condition occur yet the history, exam, and laboratory tests do not reveal another cause. Diarrhea and increased odors are common in other species with malabsorption but not that common in the horse. In many cases the horse is not depressed and has little or no fever. Colic is an inconsistent symptom. Weight loss occurs with mismanagement and in many other diseases, for an overview of this topic Chronic Weight Loss Overview.