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To understand constipation, it is important to understand how the large intestine normally works. Food passes through the small intestine where it is digested, and nutrients are absorbed. The remaining undigested material plus bacteria and some tissue from the gut lining forms the stool. The stool enters the large intestine where water is removed, and it is stored for a few hours before contractions of the intestine push the stool through the pelvic canal and out of the anus. Constipation occurs if the stool spends too long in the large intestine, too much water is removed, and the stool becomes dry and hard. These hard pellets can be difficult for the gut to move and can soon build up to a concrete mass too large to pass through the pelvis.

There are many causes of constipation, examples are:

• Management issues: the cat is inhibited from passing feces because it is being boarded in a cattery, is in pain from arthritis or after a surgery or is being antagonized by another cat at home. Some cats will refuse to use a dirty tray.
• Dehydration: many cats that eat dry food do not take in enough water. Kidney failure is another important cause of dehydration in older cats.
• Obstruction to passage of stools: especially damage to the pelvis after a road accident or the presence of a growth in, or near, the colon or rectum.
• Poor function of the colon: due to nerve or muscle damage.
• Some medical conditions and hormonal conditions.
• Foreign material in the stool: hair from the cat, especially long-haired cats and cats that are overgrooming because of stress or skin disease; hair, feathers and bone from prey.
• Obesity and inactivity: make constipation more likely.
•  Idiopathic megacolon: this is when the colon becomes weak and ineffective for a reason that is poorly understood. This is common.

Unfortunately, there is a cycle of deterioration. When defecation is painful the cat becomes less inclined to defecate and can also stop eating and become dehydrated. The stools become harder and drier and more unpleasant to pass and the problem escalates. When feces build up in the colon the intestinal walls can become stretched, damaged and eventually are unable to contract at all which will mean that the affected cat will never pass feces normally again. This is called “megacolon”.

The most common sign associated with constipation is straining to pass a motion. If your cat has a litter tray in the house, then you may notice her straining or crying in the tray but only passing small hard feces. Sometimes a small amount of liquid feces may be squeezed past the obstruction, and it may look like the cat has diarrhea. Cats may go to the litter tray frequently or refuse to go at all. They may lick around their bottom more than usual. If the constipation is more severe, they may become unwell and be unwilling to eat. Vomiting may occur. Cats with diarrhea or urinary tract problems will show similar signs.

Your veterinarian may suspect that your cat has constipation from the history you describe. They will want to examine your cat and may be able to feel the hard lumps of feces inside the colon. However, constipation is just a sign of disease and so your veterinarian will need to do other tests to try to find out what is causing the problem.

X-rays will show any abnormal pelvis. In rescued cats, owners may not know about an accident that occurred when they were young. Masses or strictures narrowing the colon or rectum can be detected by digital rectal examination (under anesthetic), endoscopy or barium-contrast x-rays. Blood and urine tests will be needed to rule out underlying problems like renal failure, low potassium and high calcium levels. Your vet will want to ensure that your cat is not suffering from urinary tract disease (FLUTD) before treatment for constipation is started.

Your vet may prescribe some laxatives or an enema to soften the stool and make it easier to pass. If your cat is dehydrated your vet may give subcutaneous or intravenous fluids to rehydrate her and soften the feces. Often it may be necessary for your veterinarian to take your cat into hospital to remove the blockage. This may be done with the use of enemas and digital manipulation under anesthetic. In some cases, surgery may be required to remove feces and in these cats part of the colon is often removed (colonectomy) when it has become stretched and non-functional.

It is important that cats pass a regular motion to keep the bowel healthy and functioning normally. Cats that have had constipation are prone to a recurrence and they are often required to have long-term treatment to attempt prevention and to avoid a major surgery.

Ensure that they have access to a clean litter tray or the outside. In multi-cat households, cats may be deterred from using the litter tray if there is competition for it so ensure that there are more litter trays than cats in the household.

Long haired cats should be brushed regularly. Encouraging your cat to exercise – regular play time with an indoor cat can help to keep them fit and active and will ward off many potential health problems.

Since dehydration is a common cause of constipation it is important to encourage your cat to drink as much as possible. Many cats will drink more from a water fountain. Dietary issues can also have an influence on stool quality but there is a lot of variation between individual cats. Adding certain fiber to the food can help in cats that are well hydrated and with mild problems take your vets advice about this. Other cats are usually better on low fiber, low residue diets. Cats are likely to be better hydrated if they avoid dry foods.

Drugs may help cats that are prone to constipation. Laxatives can be given in the long term. Some will stimulate the colon to secrete fluid, others lubricate the stool directly. Cats will often take these in their food. There are also drugs that stimulate contractions in the large bowel, but these are tablets that require long-term pill giving.