American Fancy Rat & Mouse Association

This article is from the Fall 2001 AFRMA Rat & Mouse Tales news-magazine.


Megacecum In Rats
Rat With Swollen Belly (Bloat)

Mickey Maeckelbergh, Belgium
QDo you know something about swollen bellies in rats? I have a rat from Frans that has a swollen belly like the babies in Ethiopia. I have given her Ivomec and antibiotics and asked my vet what it can be, but she doesn’t know what it is.

Answer from Karen Robbins

Rat with swollen belly.
This young Chinchilla Berkshire female rat showing a swollen belly due to “bloat.” The messy anus shows she was able to go a little. The severe cases are not able to defecate at all.

AWithout any further information from you on the rat with the swollen belly, it is hard to say, but over here there is a condition called congenital megacecum associated with certain colors of rats—namely the Chinchilla and Black-eyed Whites. It is seen occasionally in other types of rats. There is a line of Dumbos that carries it—not the stock you got from us. The babies get swollen bellies “bloat” around 3½ to 4 weeks of age, sometimes a little older. There is no cure as it is a recessive genetic trait carried by both parents. They usually die within a few days if you don’t euthanize them yourself.

From a necropsy sent in by a local breeder in 1988, the pathologist said, “The problem with the distended abdomen was due to a very large dilatation of the animal’s cecum. The cecum is a blind pouch located at the junction of the small and large intestines. It is common in herbivorous animals and serves much the same functions as the rumen of a cow. This is a condition that the animal is probably born with, although the inherited mechanism is not known. A similar condition in cats known as megacolon is rarely found and considered due to an absence of a nerve plexus that provides innervation to the colon of the cat. This lack of nerve supply allows the organ to lose its muscle tone and simply expand. A similar mechanism is probably involved with the megacecum of the rats. The only thing that can be done is to try to eliminate it from the breeding stock by not saving the parents of the animals affected for further breeding. Presumably, it is inherited as a recessive trait and normal animals may carry the trait without showing any signs of it, and yet pass it on to their offspring.”

This means you shouldn’t breed the parents ever again to anyone, nor keep any offspring from litters that produced it. Technically some of the babies should be clear, but it would take a lot of breeding to find out which ones were. The responsible thing is for the breeder to euthanize any stock that carries it himself/herself, rather than to sell them for “pets” and to just tell people not to breed the rats. Too many times, these rats are getting bred by people who don’t know or don’t think this can happen to them. That is why for so many years it is still cropping up in rats. One of our members had this happen to her from a Chinchilla rat she got from the pet store that turned out pregnant and ended up having two of the babies with bloat. She euthanized both of them and had necropsies done but I haven’t gotten the results.

Answer from Carmen Jane Booth, D.V.M.
AI have not come across any new articles on this problem in my studying as of late, and most of my books are packed. I will keep an eye out and let you know if I find anything. People who would knowingly breed these animals or animals that produce this problem should be ashamed of themselves. *

Go to the article “Megacecum and Megacolon: Development Disorders in the Enteric Nervous System in Rats”

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Updated February 13, 2015