In equine nutrition the term refers to a partial or complete obstruction of the intestine by an object or material which has been consumed by the horse. Usually this is partially digested fibrous material of a rather dry consistency obstructing the large intestine. The other common cause of impaction is sand which is consumed when the horse pulls up forage feed, usually fresh spring grass, by the roots with sand adhering to them.
Impaction at any point obstructs the normal flow of ingesta through the gut and may give rise to adverse effects with symptoms of colic. A common site of impaction is at the diaphragmatic and pelvic flexures where the large intestine (colon) changes direction, and in the caecum. Treatment may involve laxatives and/or lubricants given by stomach tube or drench in an effort to assist the breakdown and movement of impacted material. Occasionally surgical intervention may be required to resolve a serious impaction and colic.