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Function and Health of the Horse’s Small Colon and RectumBy Drs. Peter Huntington and Kathleen Crandell · March 30, 2012

The small colon is the last spot in the intestinal tract to absorb moisture from the digesta and transform it into fecal balls. The rectum is the posterior part of the digestive tract and serves primarily as a storage area for fecal products that have not been digested. Material is held in the rectum until sufficient material accumulates, which then results in nervous stimulation and voiding of feces through the anus.

Perhaps the biggest problem with maintaining a healthy rectum is to keep enough moisture in the feces so that they pass easily. Dehydration can lead to excessive water being drawn out of the fecal material into the body while it is in the small colon, causing the feces to become hard and dry. Also, certain horses have the capability of drawing more water out of the feces than others. During performances where dehydration may occur, the feces may become very dry and hard. Occasionally, these hard, dry feces become difficult to pass and can result in impaction colic.

Keeping enough moisture in the feed is very important. The easiest way to do this is to let the horse have plenty of green grass. Grass is typically 70% moisture, while hay and concentrates average only 10%. Other methods would be to serve soaked beet pulp, to dampen the hay, or to soak alfalfa pellets or cubes in water before feeding. In performance horses, such as endurance horses where water is at a premium during a competition, it is always a good idea to serve feed dampened with water.