Constipation, defined as infrequent or difficult emission of hard, dry fecal matter, is a common problem of the domestic cat. It is important to treat it fairly aggressively to prevent progression.
A variety of problems, including ingestion of indigestible material (i.e. fur), obstruction of the GI tract by foreign bodies, tumors, or strictures (narrowings), electrolyte disturbances, neuromuscular disease, and the side effects of various drugs can predispose to constipation in cats. In many cases, the specific cause of constipation in cats is undetermined, and in these cases, the condition is referred to as idiopathic constipation.
Treatment of constipation in cats involves making sure that an affected cat is well hydrated, the elimination of causative agents where possible, medical management using laxatives, enemas, and drugs that increase intestinal motility, dietary modification, and, in severe/unresponsive cases in which the colon becomes distended and unable to function properly (megacolon), surgical removal of affected portions of the colon.
Laxatives work primarily by either increasing the water content of stool or lubricating the stool so that it passes more easily. Enemas involve the irrigation of liquid through the anus and into the colon to increase fecal water content and to stimulate colonic contraction (peristalsis) to promote fecal evacuation. Enemas may be given at home to compliant cats (with appropriate training by a veterinarian), but some cats may require sedation and veterinary assistance for enema administration. Intestinal motility modifiers increase the rate and force of peristaltic contractions in the intestines.
Dietary modification usually involves the addition of either soluble or insoluble fiber (or both) to the diet to improve intestinal motility. Insoluble fiber (i.e. cellulose) works by increasing the bulk of the stool, thereby distending the colon and stimulating colonic contraction. The main disadvantages of insoluble fiber are that they lower fecal water content and that they may lower nutrient digestibility. Insoluble fiber (i.e. canned pumpkin, psyllium) is fermented in the colon, leading to the production of short chain fatty acids, which may directly promote contraction of colonic smooth muscle. Over supplementation with soluble fiber can lead to overly liquid stools (diarrhea) and can also negatively affect nutrient absorption. Fiber supplementation can be achieved by either adding fiber to the existing diet or by switching the diet to a purpose-produced high fiber diet.
Severe, non-responsive cases of constipation may progress to megacolon and obstipation (a condition characterized by permanent loss of function of affected colon). In these cases, surgical resection of the affected portions of colon may be necessary to prevent translocation of bacteria from the GI tract to the bloodstream, which can be life-threatening.