Introduction

• Rabbit megacolon syndrome (RMS) is a poorly understood disease process whereby individual rabbits have chronic intermittent diarrhea. The feces are often described as ‘cowpat’-like.
• Cause: the etiology is currently unclear, although spotted rabbits may have a genetic predisposition. There is some debate as to whether RMS covers a single condition or group of conditions, and as to whether some of the clinical signs seen may be attributed to an inflammatory bowel disease syndrome.
• Signs: chronic, intermittent diarrhea with progressive weight loss and occasional bouts of painful cecal tympany, gastrointestinal stasis and anorexia. The rabbit’s appetite between such episodes is usually very good.
• Diagnosis: no specific test for megacolon is available, but a high suspicion is raised in rabbits with chronically abnormal feces, weight loss despite a ravenous appetite, and intermittent bouts of cecal tympany and gastrointestinal stasis. The colon and cecum may be palpably distended. Blood analysis may show anemia, hypoproteinemia and hypoglobulinemia, whilst fecal cytology may show long fiber particles along with altered microbiota. Abdominal radiography may show the colon and cecum to be distended, particularly during bouts of tympany.
• Treatment: the syndrome is progressive and incurable, although symptoms may be controlled by diet and medications. The time course appears to vary widely between individuals.
• Prognosis: guarded in the long-term.

Pathogenesis

Etiology

• Currently unknown but likely to have a genetic predisposition.
• Diet may also be a factor.

Predisposing factors

General

• Generally seen in mature adult rabbits rather than juveniles.

Specific

• Certain breeds, in particular spotted rabbits such as the English spot English, appear to be predisposed.

Pathophysiology

• Not fully elucidated, but histopathology of the gastrointestinal tract often shows lymphocytic/plasmacytic inflammation.
• Fecal cytology may show long fiber particles together with altered microbiota (comprising a mixture of hard fecal pellets and cecotrophs), which suggests that the hindgut’s function of separating large and small particles is dysfunctional.
• The cecum may fill and not function properly.
• Over time, progressive malnutrition leads to signs of cachexia, a distended abdomen and metabolic derangements such as anemia, hypoproteinemia and hypoglobulinemia.
• Gas and food build-up within the gastrointestinal tract will lead to intermittent bouts of anorexia and pain Gastric dilation and stasis.

Timecourse

• Seen in mature rabbits.
• The clinical signs tend to progress slowly over months and sometimes years.

Epidemiology

• Usually an individual disease problem rather than a group issue (although related individuals may share a predisposition).

Diagnosis

Treatment

Prevention

Outcomes