Megacolon in Rabbits
Causes
The primary cause of megacolon is being a genetic Charlie (EnEn; see the page on English Spotting genetics for more details).
Other causes include viral infections (Cytomegaloviruses and Coronaviruses), imbalance of proper gut bacteria, and parasites (coccidiosis, giardiasis, Trypanosoma cruzi, roundworms, tapeworms). For these causes, treat the underlying condition.
Tumors, polyps, nerve damage, hypothyroidism, and overmedication can also cause and/or contribute to megacolon.
A Charlie patterned rabbit.
Symptoms
Affected rabbits eat in excess and produce wet, mishappen pellets. They may produce a brownish fluid from their anus, causing stains around their rear. The feces will have mucus among them. Obstipation (inability to pass feces or gas) causes severe pain, and the affected rabbit may signal this pain by grinding teeth, making moaning sounds, hunched posture, butting at its abdomen with its head, or trying to press hard against the floor to relieve pain. The first signs of an obstipation crisis are often a decrease in appetite. At this point, the rabbit may still eat treats and may eat a little of their normal pellets and hay. When feeling the rabbit's intestinal area during an obstipation, large clumps of hard material can be felt. Passing these clumps is painful and can cause sudden spasms in the rabbit.
Young rabbits with genetic megacolon (Charlie patterned rabbits) will have short, painful periods of gastrointestinal stasis and obstipation accompanied by distended abdomens, due to accumulated gas and ingested food (Gruaz et al., 2021). These will be broken up by periods of normalcy. These episodes typically increase and worsen with age. Affected rabbits often struggle to maintain weight. Symptoms worsen with age.
Kits with presenting megacolon due to being Charlie patterned must come from two English spotted patterned rabbits (bearing in mind that some colors like ruby eyed white and blue eyed white can hide broken pattern, but they still act genetically like broken pattern). They present with 10% or less total color compared to the white. Megacolon kits grow quickly for the first 4-5 weeks, often becoming larger than their non-affected siblings. Affected kits are more susceptible to death during and around weaning. Then, between 8-14 weeks, their growth slows, and their non-affected siblings catch up. Typically around the age of sexual maturity, the first clinical signs of megacolon appear. Overly wet feces which are poorly shaped are often accompanied by mucus and off-and-on diarrhea.
Megacolon rabbits are also more susceptible to infections and parasites, as well as an overgrowth of yeast. Escherichia coli infections, intestinal worms, and coccidiosis are all more likely to occur in megacolon affected rabbits.
Fecal symptoms showing progressive worsening with age in Charlie pattern megacolon rabbits..
Rabbits with megacolon have a large reduction in sodium absorption (about 50% reduction) across the cecum wall (Bodeker et al., 1995; Gruaz et al., 2021). Dry matter content increases in the wall of the small intestine and decreases in the large intestine (especially the cecum).Final stages of megacolon are severe obstipation (severe constipation with the inability to pass feces or gas). A severe dilation of the cecum (photos at bottom of the page; warning they are graphic in nature) is characteristic of megacolon. Megacolon rabbits have a shorter small intestine and a lowered pH in the duodenum. Necropsy will also show a larger than normal heart and adrenal glands. The adrenal glands also produce less than normal levels of testosterone.
Treatment
There is no cure for megacolon, but symptoms can be managed to prolong the life of an affected rabbit and reduce episodes of stasis and obstipation.
Affected rabbits should be fed unlimited fresh pellets and quality grass hay. The availability of food at all times helps prevent them from eating too fast and not wetting the food with saliva properly, which can increase the risks of stasis. Free feeding affected rabbits greatly reduces the likelihood of stasis occurring. Feeding in a bowl is idea, as it allows easy observation of how much food has been consumed. Decreased food consumption is a likely sign that an obstipation crisis is eminent. Early intervention during a crisis is crucial!
Daily gentle massages of the abdomen can promote gut healthier movements. Encouraging good levels of exercise can also promote healthier gut movements. Megacolon rabbits should be allowed a larger area to roam and be given plenty of toys to engage with.
Some great toys we suggest are:
Soulthink Rabbit Toys are excellent for promoting activity and exploration
Grass chew balls are a favorite! Rabbits love to toss these around, giving good exercise and movement
This 20 piece pack encourages a wide range of motions, including standing up, stretching, tossing, and reaching
Prevention
The best prevention is to avoid breeding Charlie patterned rabbits. Do not breed two broken colored rabbits together. Where this is impossible (as some breeds, to get the correct markings, they must be Charlie patterned; e.g. Hotots*), do not breed any rabbits which present with megacolon. Select for ones which do not. It is likely some modifying genes are involved in which Charlie patterned rabbits do and do not get megacolon (Fontanesi et al., 2014), but environmental factors are also likely involved. Any Charlie patterned rabbits should be kept in as low stress environments as possible, given a high fiber diet, and monitored closely for signs of megacolon.
This is not 100% foolproof, as the exact pattern of cells in English pattern rabbits is not entirely dictated by genetics. White spotting in animals is known to have random factors, and identical genetic clones do not have the exact same patterns.
* Please note that the Grauz et al., 2021 article states that Hotots no longer encounter megacolon. This does not appear to be correct, based on knowledge of the Hotot community and reports of megacolon still being a problem in the breed.
CAUTION: GRAPHIC IMAGES AHEAD
Please proceed down below with caution. Graphic images of necropsies (deceased rabbits showing the colon) are found below to show what megacolon looks like. Viewer discretion is advised.
Megacolon (left image) in a genetically 'Charlie' rabbit (En/En). The ascending colon is very dilated compared to the non-affected rabbit to the right. Versus a normal colon (right) in a solid patterned rabbit (en/en) (Fontanesi et al., 2014)