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Bloating & Megacolon

By Debbie “The Rat Lady” Ducommun


Updated 9/10/15


The most common cause of a bloated-looking abdomen in young female rats is pregnancy!  The next most common cause is megacolon, and much more rarely, another congenital problem or a bacterial or viral infection.


The most common cause of bloating in an adult rat is a tumor in the abdomen.  Not only can the tumor cause a bulge in the abdomen, but it can also cause fluid to accumulate in the abdomen.  Liver and kidney disease can also cause fluid to build up in the abdomen.


A rat with respiratory distress can swallow a lot of air, which she can’t burp up, causing stomach distension.  (See Other Treatments under Respiratory Disease for how to relieve the distension.)


If the abdomen is soft, it may be possible to feel if there is a tumor.  (See Health Exam.) However, some tumors are so soft they can’t be distinguished from normal organs.  If the abdomen is tight and hard because of fluid pressure, fluid can be removed from the abdomen by needle aspiration to relieve the pressure.  This will then allow palpitation for a tumor, and will also make the rat more comfortable. 


Tumors in the abdomen can sometimes be successfully removed surgically, but in many cases, if the rat cannot be kept comfortable, euthanasia is the only choice.



Megacolon is a condition where the nerves to the large intestine don’t work well and so the colon has trouble pushing out feces.  This causes the colon to become backed up, and both the colon and the stools become larger than normal.  Because the stools remain in the intestines longer than normal they can also become drier than normal and this also contributes to the problem.  However, diarrhea can also occur.  It’s a fairly common problem in rats, usually genetic, and particularly common in black-eyed white rats and rats with only small spots of color on a white background (rats with the restricted spotting gene), and sometimes in rats with a blaze. (Notice all the rats in the pictures have these color patterns.)   There is no cure.


The condition usually appears in rats 4-6 weeks of age and causes bloating, but can occasionally be found in rats a few months old.  In older rats, the colon can sometimes feel like two firm masses on either side of the lower abdomen.


Here is a 4-week-old rat with megacolon.


These pictures show a 6-month-old rat with megacolon.



For pictures of autopsies of rats with megacolon click here.


It seems that different rats can have the problem to varying degrees.  If a rat has some mobility of the large intestines, then treatment can be successful.  In a rat with little or no peristalsis, treatment may have only limited success. I know of 4 rats with megacolon who were successfully treated. I treated one boy with partial success until he died of complications at the age of 9 months. I also tried treating a younger cousin of his who died of complications at 7 weeks of age.  I’ve also seen two 4-week-old babies who were so bad they had to be euthanized.


Home treatment consists of a natural vegetable laxative called Senekot and magnesium as a stool softener to reduce the chance of a blockage. The suggested dose for the Senekot is 1/8 tablet/lb twice a day with food. Try giving  the magnesium 10-29 mg/lb twice a day, adjusting the dose until the stools are fairly soft. It’s also important to make sure the patient takes in lots of fluids and fiber by offering lots of fresh foods. Prunes can be helpful. My homemade diet is very helpful. If giving rat blocks, try soaking them in water.


If home treatment isn’t enough, ask your vet for a drug called cisapride, which is available from compounding pharmacists. Cisapride assists the colon in pushing things along.  It is best to give the cisapride on an empty stomach, at least 1 hour before or 2 hours after a meal.  The suggested dose for the Senekot is 1/8 tablet/lb once a day. This can be given with food.


It is usually also necessary to help the rat have bowel movements.  The colon, which runs along the spine from under the ribs to the anus, can be squeezed from side to side “like a tube of toothpaste” from top to bottom to help push things along.  It may also be necessary to pinch the area just under the tail to help feces come out of the anus.  A sliver of a suppository can also be inserted into the anus.


Helping squeeze out the colon on a rat with megacolon.



Urinary Blockage

Another possible cause of a rat who looks bloated is an overfilled urinary bladder, which will feel like a balloon in the center lower abdomen.  Normally the bladder will only be ½" across or less, but if blocked can become 2" across.  This is an emergency.  A veterinarian can suck out some of the urine with a needle and syringe to make your rat more comfortable, and do a urinalysis to try to figure out the cause of the blockage.


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