Inflammatory Bowel Disease
Basic Information 
Epidemiology
Genetics and Breed Predisposition
• Some studies report increased incidence in Standardbreds and Thoroughbreds, although this may represent regional equine populations rather than true breed predispositions.
• Granulomatous enteritis has been described in some related horses, suggesting a potential genetic predisposition, although this has not been definitively documented.
Clinical Presentation
Physical Exam Findings
• Temperature, pulse, and respiratory rate are usually within normal limits.
• Ventral edema (caused by hypoproteinemia) is frequently present.
• A generalized, exudative, crusting dermatitis and ulcerative lesions on the coronary bands are often present in horses with MEED.
May be within normal limits, although focally or diffusely thickened small intestine is often appreciated
• In contrast, initial evaluation of horses with focal eosinophilic enteritis is identical to horses presenting for other causes of nonstrangulating small intestinal obstruction (see “Enteritis, Focal Eosinophilic” in this section).
Etiology and Pathophysiology
• The specific etiology of all types of IBD is unknown. Infectious, toxic, allergic, or autoimmune mechanisms have been postulated to play a role. IBD has been reported in horses after Salmonella or parasitic infections and in horses that may have ingested feed contaminated with aluminium.
• In most cases, though, by the time clinical signs are evident, the primary pathology appears to be immune mediated in nature, even though an initial toxic, dietary, or infectious insult may have initiated the pathology.
• In some cases, IBD may represent a chronic hypersensitivity reaction to unknown (likely dietary) antigens.
• Regardless of the inciting cause, intestinal inflammation results in dysfunction of the intestinal villous epithelial cells, resulting in malabsorption and maldigestion of nutrients and causing weight loss and hypoproteinemia. With severe inflammation involving the submucosal vasculature, plasma protein is also lost.
• Partial intermittent small intestinal obstruction with hay and fibrous feed caused by small intestinal thickening is likely the cause of intermittent colic in IBD.
• In most cases of IBD, the predominant inflammatory infiltrates are found in the small intestine, although colonic involvement does occur, and some lesser degree of inflammation is usually evident on histopathologic evaluation of the entire intestinal tract in most affected horses.
• In MEED, inflammatory infiltrates are found in the skin, liver, pancreas, and large intestine in addition to the small intestine. The reason these locations are targeted is not known.
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