Colic, Equine - contd.
The gastrointestinal system is the most common source for colic. Lesions of the stomach, small intestine or large intestine must be considered when assessing a patient with colic. Increased motility and spasm of the bowel are common self-limiting causes of colic; normal intestinal contractions are perturbed by many influences, including inflammation, intestinal parasites and moldy feeds. Gas distension of the large intestine frequently causes clinical signs of colic. This distension may result from abrupt changes in diet, poor quality diet, or heavy intestinal parasite burdens, with or without a recent history of deworming.
Obstructive processes of the large or small bowel can be characterized as simple obstructions or those that are strangulating obstructions, associated with substantial interruptions of blood supply. Impaction of the large intestine with feed or sand is a leading cause of colic in adult horses. Coarse feeds, poor dentition and dehydration may predispose a horse to the simple obstruction caused by feed impaction. Horses residing in sandy regions or animals fed hay grown in those areas may ingest more sand than is desirable, permitting obstruction of the bowel with sand.
There are several less common causes of intestinal obstruction. Enteroliths, or mineral concretions, that form in the bowel may cause obstruction; these are more common in California where hay contains a high level of magnesium. Young patients especially may develop obstruction from eating foreign material, such as bedding or rope. Adhesions or tumors may cause obstruction, and rarely, strangulation of the bowel's blood supply. Similarly, hernias of the abdominal wall, inguinal area or umbilicus can entrap a section of bowel, causing blockage and impaired blood circulation. Internal herniation, intussusception, or telescoping of the intestine, or torsion may occur as primary problems, or in response to any cause of altered motility, such as parasites or diet change.
Newborns may develop colic from fecal impaction or gastric ulcers associated with stress. Foals and yearlings may become impacted with
Parascaris equorum, or roundworms, after deworming. In horses of all ages migration of the parasite
Strongylus vulgaris and other large strongyles contribute to colic by stimulating inflammation in the gastrointestinal vessels along its migratory path. The blood vessels become occluded or obstructed with blood clots, depriving the gastrointestinal tissues downstream of oxygen. Diminished blood supply may alter motility, contributing to functional obstruction, and may even cause perforation of the bowel as those tissues become devitalized.
Inflammatory conditions of the small or large intestine may also cause substantial pain and functional obstruction. Enteritis and colitis must be discriminated from processes causing blockage or mechanical obstruction.
Reproductive problems such as uterine torsion, retained placenta, or tears of the uterus or cervix are common problems outside the gastrointestinal tract that produce signs of colic. Urinary tract disease, acute liver pain, or abdominal abscesses all are likely to produce signs of colic.
