Impaction colic is one of the most common causes of colic. However, Dr. Sarah Freeman indicates at thehorse.com that many mild impactions may be missed by owners and even veterinarians. Impactions can cause severe pain and some require surgery while others are so mild that the horse does not even seem painful. In some of the mild cases, the horse may only lie down more than normal, eat less feed or pass a reduced amount of manure, so unless you are watching your horse closely, you may not know anything is wrong.
Impactions of the small intestine are generally more painful and acute than those of the large colon so the location makes a difference in clinical signs. It is critical that impactions are treated early because many of them are related to dehydration, and an area of the intestine becomes dry and prevents movement of ingesta. The longer you wait, the dryer the area becomes and the harder the impaction becomes. Studies show that up to 50% of the mild and early impaction cases resolved with only minor treatment, while about 30% required additional treatment and only about 9% were severe. However, when you see your horse having a colic episode, you don't know which category your horse falls into, so you have to treat it. Failing to treat or delaying treatment increases the chance the horse will progress to a more serious stage of colic. This delay is especially important considering dehydration as the sooner that fluids are instituted in a horse that is not drinking, the greater the chance for survival and the less expensive it will be. So if your horse is not eating well or lying down more than normal, a mild colic may be involved and treatment is recommended.