Causes of constipation include:
Reluctance for any behavioural reason, such as a dirty tray or competition from other cats, or any medical reason, such as pain when defecating, to use the litter tray.
Matter such as hair, foreign material or bone in the large intestine.
Cats that are dehydrated reabsorb more fluid from the colon. As a result the stool becomes hard and dry. Chronic renal failure is a common cause of dehydration.
Injuries can damage either the nerves that control contraction of the bowels or the pelvic canal through which the colon passes. Either of these forms of injury can cause constipation. (Some injuries cause the opposite, a lack of sphincter muscle control and consequent faecal incontinence.)
In idiopathic megacolon, the smooth muscle that normally contracts to propel the faeces towards the rectum loses its ability to do so. Although the cause is not known, this is, in my experience, the most common cause of constipation in older cats.
Prevention and Treatment
Chronic constipation is a very common problem especially in older cats. Early and uncomplicated constipation usually responds to diet changes and lubricant laxatives. More chronic or complicated constipation is more difficult to control, takes dedication on your part and may require surgery to improve, although surgery is not always a cure.
Laxatives loosen bowel contents to allow stool to pass through the colon. Some act as lubricants while others stimulate the colon to greater activity. Cats should be well hydrated before being given laxatives as most of them lead to water retention in the colon.
Mild constipation may be relieved with a small lubricant laxative. In more severely affected cats we need to give a cat a warm water enema, usually under general anaesthesia. with manual evacuation.
These improvie neuromuscular transmission and are useful in mild to moderate cases of megacolon. None are licenced for use in cats so they are given with your ‘informed consent’.
An intravenous drip is often needed to overcome dehydration. At home, a cat's hydration is improved by switching from dried kibbles to wet food and by adding water to the food. To treat chronic dehydration we can show you how you can give daily subcutaneous fluids.
Surgery is sometimes needed, to remove the permanently damaged portion of the colon.