Large bowel diarrhea develops when the colon’s capacity to resorb water or store feces decreases. Mucosal damage and inflammation can lead to hematochezia and mucus in the stool. Multiple disease processes can result in large bowel diarrhea, some of which can be challenging to definitively diagnose. Despite extensive testing, many diagnoses are based on response to treatment.4 Following an evidence-based treatment protocol may circumvent advanced diagnostics and increased costs.7
Large bowel diarrhea can respond to parasiticides, antibiotics, or diet changes. Trials of highly digestible GI diets or diets with novel or hydrolyzed protein can be given safely in many cases. Overall, many enteropathies are food responsive.4,6,7 Younger dogs with large bowel diarrhea are likely to respond to diet change (eg, highly digestible diets, hydrolyzed diets, high-fiber diets) alone.4 Dogs that do not respond to highly digestible or novel-protein diets may benefit from a high-fiber diet or psyllium fiber supplementation.
Fiber-responsive large bowel diarrhea is a subset of chronic idiopathic large bowel diarrhea (a diagnosis of exclusion) that may overlap with irritable bowel syndrome or other stress-related issues.1-3,5,8 Chronic idiopathic large bowel diarrhea may account for 20% to 25% of referral cases,1,5 but prevalence in the general population is less understood. Clinical signs may be potentiated by stress, certain dietary triggers, or other factors not currently understood, but specific signs are not predictive of response to fiber.
Dietary fiber is classified by structure, solubility, viscosity, fermentability, ability to adsorb substances, and effect on GI physiology. Viscosity and fermentability are especially pertinent to digestive health. Viscous gels slow gastric emptying, increase small intestine transit time, and slow absorption or reduce digestibility of some nutrients.9,10 Fermentation by gut microflora has the potential to be highly beneficial but can be detrimental if excessive.
Patients with chronic idiopathic large bowel diarrhea that respond well to fiber supplementation or a high-fiber diet generally have a positive prognosis. Fiber-responsive large bowel diarrhea can affect dogs of any age, weight, or breed, and clinical signs are commonly intermittent.1,5 Despite primarily affecting the large bowel, reduced appetite, abdominal pain, slight weight loss, and frequent vomiting are possible.
Success of psyllium or other fiber supplementation with a desirable insoluble:soluble fiber ratio and fermentability in cases of fiber-responsive large bowel diarrhea is likely multifactorial. Duration of treatment and ability to decrease or discontinue fiber supplementation in patients with fiber-responsive large bowel diarrhea is variable.1,5 In one study, up to 50% of dogs appeared to tolerate a decrease or discontinuation of fiber supplementation after 2 to 3 months.3 Some patients benefit further from additional treatments (eg, behavioral therapy, probiotics, medical management).1,5,8