Chronic Diseases of the intestinal tract Causing constipation

8. Chronic Diseases of the Intestinal Tract Causing Constipation

Constipation is defined as infrequent defecation, of excessively dry or hard feces. It is commonly accompanied by increased straining to defecate. Causes of constipation are listed in Table 27.

Obstipation is defined as an inability to pass feces, and arises when constipation is prolonged resulting in formation of progressively harder and drier feces. Defecation becomes increasingly more difficult, until it is virtually impossible because of secondary degenerative changes in colonic muscle.

Megacolon is a descriptive term for a persistent, generalized enlargement of the diameter of the colon. It may be congenital or acquired, with the acquired cases arising secondary to numerous disorders including fluid/electrolyte imbalances (especially hypokalemia), dietary problems (low residue diet, ingestion of foreign material), painful defecation, neuromuscular disorders and colonic obstruction.

Colonic impaction usually occurs with a mixture of feces and ingested hair, bones etc. Recurrent bouts may lead to secondary megacolon / obstipation. The main clinical sign of constipation is tenesmus, with multiple unsuccessful attempts to defecate. Occasionally animals may pass scanty liquid feces around the impaction and the owner thinks animal has "diarrhea". Other signs include vomiting and dyschezia (painful or difficult defecation).

Diagnosis and Treatment

Diagnosis of constipation involves first confirming that the large intestine is the organ involved e.g., by ruling out other possible causes of tenesmus (urogenital tract diseases). The presence of fecal matter within the large intestine can be confirmed on physical examination by abdominal and rectal palpation. This enables the differentiation of constipation from colitis as a cause of tenesmus. Radiography will confirm the diagnosis and enable predisposing factors to be identified e.g., pelvic canal narrowing from previous pelvic fracture. Other diagnostic measures (e.g., laboratory analyses) are required to assess for metabolic diseases as an underlying cause.

Treatment involves first rectifying the underlying cause if possible e.g., perineal hernia repair. Options for medical management are listed in Table 28. If megacolon has developed surgical management may be necessary e.g., subtotal colectomy.

Dietary Management of Colonic Diseases Including Constipation, Obstipation and Colonic Impaction

Dysfunction of the colon can be related to different etiologies. Nutritional treatment includes restriction of dietary antigens, as already described for patients with allergy, and the addition of ingredients that help to modify intestinal motility. Further, diet composition is an important determinant for the water holding capacity of the undigested material reaching the colon.

Some cases of constipation will respond to an increased fiber content of the diet. Fiber sources have to be selected according to their physiological properties.

• Dietary fiber with a low solubility e.g., cellulose, increase the bulk in the intestine and may help to regulate intestinal motility. Besides their effects on motility, insoluble fiber has a certain capacity to bind non-absorbed fluid by physical forces. Therefore, fecal quality of patients with colonic disorders may improve by the addition of small amounts of insoluble fiber. The disadvantage of higher amounts of insoluble fiber is, that these ingredients lower the digestibility of the diet. Therefore, the concentration of insoluble fiber needs to be carefully controlled.
• Other types of fibers are suitable for patients with colonic disorders due to their higher solubility. Typical examples include beet pulp, pectins from carrots or fruits, and gum-like fiber e.g., guar gum or psyllium. These fiber sources have a different structure compared to cellulose, and can, with the exception of psyllium, be fermented by intestinal bacteria. Negative effects of higher amounts of soluble dietary fiber include increased moisture content of the feces which, when in high amounts can negatively impact fecal quality.
• The fermentation processes induced by the ingestion of fermentable fibers have a strong impact on the colonic milieu, because bacteria release organic acids as products of the metabolism that tend to reduce the colonic pH. The short chain fatty acids that are released by bacteria can be partly utilized by the colonic mucosa. Improved supply with butyric acid has beneficial effects in humans suffering from colitis. The organic acids can also have some regulatory effects on motility. Furthermore, the addition of fermentable dietary fiber reduces the concentration of some bacteria that can be considered potentially harmful and increase the concentrations of some bacteria that are regarded as being beneficial.

The Composition of the Diet Must Be Based on the Nature of the Digestive Complaint Encountered

Swallowing Conditions - Choose a ration type that is concentrated in energy, high in fats, and adapted to cachexic conditions.

Gastrointestinal Conditions - The same type of diet may be used, except in cases of fat intolerance. Focus on a diet containing a moderate lipid level, adapted to hyperlipidemia.
In some cases (increase in intestinal permeability, IBD, intolerance reaction or dietary allergy), a hypoallergenic diet constitutes the best alternative.

Colonic Conditions - While many cases of chronic colitis respond well to a hypoallergenicdiet, disruptions to digestive transit are sometimes resolved by increasing the fibercontent in the ration.

Although these ideas need further investigation, the addition of moderate amounts of insoluble/non fermentable and soluble/fermentable dietary fiber is common in practice and seems to work in many patients with chronic colonic disorders. It may be necessary to investigate the effects individually and to adjust the amount of fiber according to the tolerance and the clinical effects in the patient. In cases with severe problems due to constipation or fecal impaction the laxative effects of soluble fiber sources are used specifically for treatment. In those patients the application of fermentable carbohydrates, e.g., lactulose or lactose is possible. Again, the dosage needs to be adjusted individually. As a general rule, the dosage should be altered to produce a slight increase in fecal moisture. The fecal pH normally drops from values above 7 to 6.5. In those cases where owners prefer to use common feedstuffs, wheat bran is a good additive that increases the fiber content of a diet and has regulatory effects on the gut motility. Ingredients with laxative properties are liver, milk and milk products (Willard et al., 1994; Zentek et al., 2002; Guilford & Matz 2003).