• 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.

Presenting signs

• Chronic abnormal feces, ranging from ‘cowpat’-like, to soft but variable in size including very large fecal pellets Diarrhea: overview. The feces often appear to be a mixture of pellets and cecotrophs, ie long fiber particles with cecal micro-organisms, but not normal pellets or cecotrophs .
• Over an extended period of time, the rabbit will lose condition whilst the abdomen becomes distended.
• The rabbit’s appetite is often ravenous, other than during intermittent periods of cecal tympany and gastrointestinal pain.

Acute presentation

• Often an acute-on-chronic presentation whereby the rabbit shows acute signs of abdominal pain and anorexia Anorexia secondary to the chronic megacolon signs.

Geographic incidence

• Cases have been reported worldwide, but it appears to be rare.

Age predisposition

• Tends to be seen in mature rabbits, generally over 3 years old.

Gender predisposition

• No obvious sex predisposition.

Breed/Species predisposition

• Rabbits with spotted markings, such as the English Spot, appear to have a genetic predisposition, although cases have been seen in non-spotted rabbits.
• Various papers indicate a genetic predisposition in certain breeding populations.
• Hybridization may influence the disease but doesn’t affect inclination to megacolon in EnEn homozygous spotted rabbits.

Public health considerations

• No public health concerns known at this point.

Cost considerations

• The condition is progressive and so the rabbit is likely to need ongoing dietary management and potentially medications.
• There may be intermittent bouts of abdominal pain and gastrointestinal stasis Gastric dilation and stasis which may need to be managed medically, potentially requiring hospitalization Hospitalization/nursing care.
• Owner should be counselled on the potential costs.

Special risks

• No specific risks.