The pelvic flexure is the narrowest part of the large colon. It is the place where the large colon doubles on itself, producing a similar shape to a toilet U tube. Not surprisingly, this is the site where food accumulates if a horse becomes constipated. Pelvic flexure impactions and spasmodic colic are extremely common causes of colic in the horse.

Impaction can be described as a severe constipation ~ the horse is unable to pass manure. Insufficient water intake, insufficient fiber intake, a “sluggish” intestinal movement, and other conditions of the digestive tract may cause impaction.

Causes: Pelvic flexure impaction can result from sudden changes in feed, excessive consumption of grain or lush pasture, dehydration, by ingestion of foreign material, by ingesting too coarse hay or too much straw when not accustomed having the latter as bedding. Ingested grain or grass may produce by-products that suppress the normal movements of the intestinal wall, while foreign material, such as wood chewed from fences (wood shavings or sawdust ingested with hay), can become lodged in the intestine and block the passage of gut contents. It can also occur in autumn and winter as horses are brought in of grass to stables but is also fairly common in animals which are quite fit and in a lot of work but which then receive an injury requiring them to be completely box rested.

Signs: Diagnosis is fairly easy with most horses: the stall does not have the normal amount of manure in it. However, some horses may pass large amounts of mucus and/or watery diarrhea, without normal manure, when they are impacted. Some horses show only mild pain, but go off their food, whereas others are violently colicky. Pain is often intermittent. Fecal output will be markedly reduced, and feces are drier than normal. Heart and respiratory rates may be elevated, consistent with pain, but will return to normal during pain-free periods. Gut sounds vary from normal to reduced. A large pelvic flexure filled with stodgy feces will be felt on rectal examination, but peritoneal fluid will be normal and little or no fluid will be obtained from the stomach when the stomach tube is passed.

Treatment: Impactions are treated by lubricants (e.g., mineral oil), water, and agents that add bulk and/or make the stool more soft (dioctynate, DSS, docusate, Sileum). These must be given by the veterinarian by stomach tube. Severe impactions, which may have developed over several days, could require the administration of fluids via a drip into the vein in order to rehydrate the animal. Pain relief may be provided by the use Dipyrone or a similar drug.

Drugs that stimulate the intestinal tract, such as terpasol, and Peristal, are sometimes used to treat impaction. However, these drugs can be dangerous: if the segment of intestine involved has been damaged or weakened, they can lead to a rupture. Further treatment and prevention for impaction centers on dietary adjustments. The horse should be given adequate water, and fiber, and special dietary additions, such as liberal amounts of grazing and/or bran mashes, may be prescribed.


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