Inflammatory Bowel Disease

TL;DR. Inflammatory Bowel Disease (IBD) is a chronic, immune-mediated inflammation of the digestive tract in dogs and cats that requires long-term management through tailored diets, targeted medications, and close veterinary supervision.

IBD can affect any part of the gastrointestinal tract, including the stomach, small intestine, and colon.

What is it?

Inflammatory Bowel Disease (IBD) is not a single disease, but rather a group of chronic, idiopathic (unknown cause) gastrointestinal disorders characterized by persistent inflammation of the digestive tract lining. In a healthy dog or cat, the mucosal lining of the intestines is a highly organized barrier designed to absorb nutrients while keeping harmful bacteria and toxins out. In animals with IBD, this barrier becomes compromised. The body's immune system overreacts, sending a massive influx of inflammatory white blood cells into the delicate layers of the gut wall.

This cellular infiltration causes the lining of the digestive tract to become thickened, red, and irritated. As a leading veterinary internal medicine reference notes:

"Infiltration with inflammatory cells leads to thickening of the intestinal absorptive surface and decreased absorptive capacity. Different types of IBD are found in the dog and cat, and classification is based on the primary type of inflammatory cell infiltrate. Lymphocytic-plasmacytic is the most common form of IBD, but eosinophilic and granulomatous forms also are reported. Prolonged or extensiv" — Small Animal Critical Care Medicine, p.711

When the gut wall thickens, it loses its ability to properly digest and absorb nutrients from food. This leads to the classic clinical signs of chronic diarrhea, vomiting, and progressive weight loss. Because the disease is chronic, it is a lifelong condition that cannot be cured, but it can be successfully managed to provide your pet with an excellent quality of life.

Causes & risk factors

While the exact cause of IBD remains unknown, veterinary scientists believe it is a multifactorial disease. It is widely accepted that IBD arises from a complex, abnormal interaction between the pet's immune system, their genetic predisposition, the normal bacterial population of the gut (the microbiome), and dietary proteins.

Several factors can trigger or exacerbate this abnormal immune response:

• Dietary Antigens: Proteins in standard pet foods can sometimes be recognized as foreign invaders by an overactive immune system, triggering localized inflammation.
• Microbial Imbalance: An imbalance in the gut bacteria (dysbiosis) can disrupt the mucosal barrier, allowing bacteria or their toxins to penetrate deeper into the intestinal wall.
• Genetic Predisposition: Certain breeds are diagnosed with IBD more frequently than others, strongly suggesting an underlying genetic component that influences how their immune systems interact with the gut environment.

In cats, a specific and severe form of inflammation known as eosinophilic enteritis can sometimes occur. A prominent veterinary textbook explains:

"Some cats have eosinophilic enteritis as part of a hypereosinophilic syndrome (HES). The cause of feline HES is unknown, but immune-mediated and neoplastic mechanisms may be responsible. Less severely affected cats without HES seem to have a condition similar to cani" — Internal Medicine, p.506

Signs to watch for

The symptoms of IBD can wax and wane over time, often starting as mild, occasional digestive upsets that gradually become more frequent and severe. Because IBD can affect the stomach, small intestine, large intestine, or all three, the symptoms can vary widely depending on which part of the gastrointestinal tract is most severely inflamed.

Common Symptoms

• Weight loss: This is a hallmark sign of small intestinal IBD. Even if your pet has a normal or increased appetite, they cannot absorb nutrients properly, leading to progressive muscle and fat loss.
• Soft stools or chronic small intestinal diarrhea: Stools are typically large in volume, watery or semi-formed, and passed with normal frequency or only slightly increased frequency.

Occasional Symptoms

• Vomiting: More common when the stomach or upper small intestine is inflamed. In cats, chronic vomiting is often mistaken for simple "hairballs" when it may actually be an early sign of IBD.
• Hematochezia (bright red blood in the stool): This occurs when the large intestine (colon) is inflamed, a condition known as colitis.
• Hypoalbuminemia and Panhypoproteinemia: These are low levels of proteins (specifically albumin) in the blood. When the intestinal lining is severely damaged, vital proteins leak out of the blood vessels and into the gut, where they are lost in the stool. This is known as Protein-Losing Enteropathy (PLE).
• Hypocholesterolemia: Low blood cholesterol levels can occur due to severe malabsorption of dietary fats.

Chronic weight loss and a poor appetite are common signs of advanced small intestinal IBD.

How vets diagnose it

Diagnosing IBD is a step-by-step process of exclusion. Because many other diseases can cause chronic vomiting, diarrhea, and weight loss—such as intestinal parasites, pancreatic disease, liver failure, kidney disease, and food allergies—your vet must rule these out first.

Your vet will likely begin with baseline bloodwork, a urinalysis, and fecal testing. They may also recommend specialized blood tests to check vitamin levels (folate and cobalamin), which are often depleted in pets with small intestinal disease.

If these initial tests do not reveal an underlying cause, the next step is typically an elimination diet trial. This helps determine if your pet has a food-responsive enteropathy rather than true, idiopathic IBD. If the pet does not respond to dietary changes, advanced imaging like an abdominal ultrasound may be recommended to visualize the thickness and structure of the intestinal walls.

The gold standard, definitive diagnosis of IBD requires obtaining tissue biopsies of the stomach and intestines. This is performed either via endoscopy (inserting a tiny camera into the digestive tract) or surgical laparotomy. These biopsies are then evaluated by a veterinary pathologist (histopathology). Obtaining high-quality biopsies from multiple locations is critical to ensuring an accurate diagnosis, as a leading internal medicine textbook warns:

"If the biopsy specimens are of marginal quality (either from the standpoint of size or artifacts present), it is easy to mistakenly diagnose LPE instead of lymphoma, especially if the latter is causing a secondary tissue reaction. Biopsy of more than one site (e. g. , duodenum and ileum, as opposed to just duodenum) is sometimes critical in finding inflammatory and neoplastic changes." — Internal Medicine, p.507

Treatment options

Once a diagnosis of IBD is confirmed, your vet will design a multi-tiered treatment plan. Because every pet's immune system and gut microbiome are unique, treatment often requires a trial-and-error approach to find the most effective combination.

First-Line Therapies

• Dietary Modification: Many pets with mild to moderate IBD can be managed with diet alone. Your vet will recommend either a hydrolyzed protein diet (where the protein molecules are broken down so small that the immune system cannot recognize them) or a novel protein diet (utilizing a protein source your pet has never eaten before, such as venison, kangaroo, or alligator). High-fat diets are generally avoided in dogs because fat is difficult to digest, though cats do not necessarily require low-fat elimination diets to respond. As noted in veterinary literature:

"It would be best to try one and, if unsuccessful, then try the other. High-fat diets are generally avoided in such patients (because fat is difficult to digest), but there is no evidence that elimination diets have to be low in fat to be effective in cats. Most dogs and cats that respond to an appropriate diet do so within 3 weeks, although some take longer." — Internal Medicine, p.506

• Glucocorticoids (Corticosteroids): These are powerful anti-inflammatory medications used to suppress the overactive immune response in the gut. Prednisolone is the most commonly used steroid. Budesonide, another glucocorticoid, is highly effective because it acts locally within the gut wall and is rapidly broken down by the liver, minimizing the systemic side effects typically associated with steroids (such as excessive thirst and urination).
• Antibiotics and Antiprotozoals: Metronidazole is frequently prescribed for its dual action: it targets harmful anaerobic bacteria in the gut and exerts a mild anti-inflammatory effect on the intestinal lining. Enrofloxacin, a fluoroquinolone antibiotic, may be utilized in specific cases, particularly in breeds prone to severe, bacterial-associated colitis.

Second-Line Therapies

If your pet does not respond to first-line therapies, or if they have severe disease with life-threatening protein loss, your vet will introduce stronger immunosuppressive medications or localized anti-inflammatories:

• Immunosuppressants: Medications such as Azathioprine (used primarily in dogs), Chlorambucil (often preferred in cats), or Cyclosporine may be added to the regimen. These drugs work through different pathways to quiet the immune system, allowing your vet to eventually lower the dose of steroids.
• Local Anti-inflammatories: For pets suffering primarily from colitis (large intestinal IBD), medications like Olsalazine Sodium, Olsalazine, or Sulfasalazine may be prescribed. These drugs deliver targeted anti-inflammatory action directly to the colon.
• Targeted Enemas: In rare, severe cases of distal colitis (inflammation at the very end of the colon), localized treatment may be necessary. A leading textbook notes:

"Retention enemas of corticosteroids or 5-aminosalicylic acid are rarely indicated in animals with severe distal colitis. The dose is estimated from the human dose. These enemas place large doses of an antiinflammatory agent directly on the affected area while minimizing systemic effects. Although effective in controlling the clinical signs,their administration is unpleasant for both clients and an" — Internal Medicine, p.456

An endoscopic biopsy allows veterinarians to visualize the inflamed gut lining and collect tissue samples for a definitive diagnosis.

Prognosis

The prognosis for pets with IBD is highly variable and depends on the severity of the inflammation, which parts of the digestive tract are affected, and how early the disease is diagnosed.

Pets with colonic IBD (colitis) generally have a better, more predictable prognosis than those with small bowel IBD. Many dogs and cats with mild to moderate IBD respond exceptionally well to dietary changes and initial steroid therapy, allowing them to live a normal, active lifespan with minimal flare-ups.

Conversely, pets with severe small intestinal IBD, or those who have developed Protein-Losing Enteropathy (PLE) with severe hypoalbuminemia, have a guarded prognosis. These cases require aggressive, lifelong medical management, frequent veterinary monitoring, and carry a higher risk of complications.

Prevention

Because Inflammatory Bowel Disease is an idiopathic condition with no single known cause, there is currently no way to prevent it. There are no genetic screening tests available for pet owners.

The best way to protect your pet is to maintain them on a consistent, high-quality diet, avoid sudden dietary changes, and seek prompt veterinary care if you notice chronic or recurring digestive issues. Early intervention can prevent the chronic, irreversible thickening of the gut wall that makes IBD much harder to manage later in life.

When to call your vet

You should schedule an appointment with your vet if your pet experiences soft stools, diarrhea, or vomiting that lasts for more than a few days, or if you notice gradual, unexplained weight loss despite a normal appetite.

You must seek emergency veterinary care immediately if your pet exhibits any of the following red-flag signs:

• Extreme lethargy or weakness
• Swelling of the limbs, face, or a distended, fluid-filled abdomen (signs of severe protein loss)
• Persistent, uncontrollable vomiting that prevents them from keeping water down
• Black, tarry stools (melena), which indicate bleeding in the upper digestive tract

For specific breeds

Several breeds have a suspected genetic predisposition to developing IBD, and some present with unique, breed-specific variations of the disease:

• Boxers and French Bulldogs: These breeds are uniquely susceptible to a severe, invasive form of colitis known as histiocytic ulcerative colitis (or granulomatous colitis). This form of IBD is associated with an inability to clear specific E. coli bacteria from the gut wall and often requires targeted antibiotic therapy with Enrofloxacin rather than standard immunosuppressants.
• Soft Coated Wheaten Terriers: This breed is highly predisposed to a severe, concurrent presentation of Protein-Losing Enteropathy (PLE) and Protein-Losing Nephropathy (PLN). They lose vital proteins through both their inflamed intestines and their kidneys, requiring aggressive, early, and lifelong multi-drug therapy.
• Basenjis: Basenjis can develop a severe, breed-specific form of immunoproliferative enteropathy characterized by severe diarrhea, weight loss, and progressive wasting that requires intensive immunosuppressive management.
• German Shepherd Dogs: This breed is frequently diagnosed with chronic enteropathies and immunologic gut imbalances. They often require a meticulous combination of dietary elimination trials, antibiotics, and long-term immunosuppressive therapy to control their symptoms.

Sources

• Small Animal Critical Care Medicine, Page 711
• Internal Medicine, Pages 456, 506, 507