Impaction of the small colon has been recognized in horses for many years, but recently it has become apparent that a form
of this disease differs from simple fecal impaction of the colon.
Extensive small-colon impactions are best treated by performing a small-colon enterotomy followed by extensive lavage of
the entire length of the small colon.
Specifically, horses may develop small-colon impaction during or following an episode of diarrheal disease. This can be very
confusing for veterinarians evaluating these cases because horses with active diarrhea typically are not suspected of having
The pathophysiology is thought to relate to inflammation of the small colon wall, most likely induced by an infectious organism
with edematous mucosa reducing the size of the lumen, the result of which is impaction.
Recently at North Carolina State University (NCSU), we have noticed that specific farms have outbreaks of small-colon impaction.
Horses will present with signs of infectious diarrhea, including fever, low white blood cell counts and watery feces. These
cases are the subject of an ongoing epidemiological study at NCSU by Drs. Lisa Federico and Anthony Blikslager.
Additional signs, including colic and distended small colon on rectal examination, are suggestive of small-colon impaction.
In most instances, the small colon impaction itself can be detected, although it can be difficult to identify when it is markedly
distended. Unique organisms that might be associated with small colon impaction have been investigated at NCSU, including
viruses, but none have been identified to date.
Culturing for Salmonella, as with any diarrheal case, is indicated, and it certainly is possible that Salmonella could induce
small-colon inflammation and impaction.
One particularly confusing finding in some horses with small-colon impaction is the concurrent presence of diarrhea. In these
cases, it is thought that colonic fluid is able to move around the impaction, and it is not absorbed by the small colon because
of inflammation. Therefore, a horse with diarrhea that becomes painful, particularly if there is development of abdominal
distension, should have a rectal examination to assess the possibility of a small colon impaction.
Small-colon impaction may be treated medically, including administration of fluids, flunixin meglumine, broad-spectrum
antibiotics for horses that appear to be endotoxemic and administration of mineral oil by nasogastric tube. Balanced electrolyte
solutions (made up of table salt and lite salt) also can be administered by stomach tube, which has been shown to soften fecal
material more efficiently in recent studies compared to intravenous fluids (see Suggested Reading).
Additional treatment for pain can include xylazine and butorphanol (150-200mg and 5-10mg, respectively, for a 1,000-pound
adult horse). However, veterinarians should be cautious about treating pain aggressively because more than 50 percent of these
cases ultimately will require surgery, and excessive treatment of pain might delay referral or surgery.
Indications for surgery include refractory pain, lack of response to medical therapy and progressive distension of small and
When palpating horses with this condition, it can be difficult to determine which segment of the colon is impacted or distended.
There are occasions where the impaction is within reach inside the rectum, although veterinarians should be very cautious
about attempts to remove the impaction with enemas because the small colon likely is inflamed and can rupture.
As the disease progresses, the small colon will become distended, and may feel like large colon. However, the diameter is
not as large as the large colon, and loops of distended small colon can be felt within the caudal abdomen, including the pelvic