Equis ISSN 2398-2977

Colon: impaction

Contributor(s): Roberta Baxter, Peter Rakestraw


  • Colonic impaction (or accumulation of ingesta in the colon that causes obstruction) is a cause of colic.
  • Pelvic flexure impactions, the most common cause of colonic impactions, accounted for 5% of cases of colic seen by one first opinion practice.
  • Cause: poorly digested food, ingestion of sand, changes in management and/or feeding, abnormalities of dentition, stress, etc.
  • Signs: chronic low grade colic, that is generally present over several days. There may be secondary dehydration, but cardiovascular compromise is usually minimal.
  • Diagnosis: rectal examination is usually diagnostic for pelvic flexure impactions but may not be diagnostic for right dorsal colon impactions.
  • Treatment: medical treatment with fluids, analgesics and laxatives is generally effective, although surgery is indicated in a minority of cases.
  • Prognosis: usually good in medical cases.



  • Most colonic impactions occur in the large colon, particularly at the pelvic flexure and right dorsal colon. Impactions arise most commonly at sites where there is transition of intestinal movement, at sphincters between different segments of intestine, or at regions of intestinal narrowing. The causes in many cases remain unknown but possibilities include:
    • Poor teeth and thus poor mastication of food.
    • Stress associated with transport, etc.
    • Inadequate or inappropriate food (coarse roughage).
    • Parasitism.
    • Systemic dehydration.
    • Eating of bedding or other inappropriate material that is poorly digested.
    • Gastric ulceration, intestinal adhesions.
    • Lack of sufficient water.
    • Sudden change in management, especially exercise or diet.
  • Cases are particularly common in horses that are suddenly put onto box rest, in many cases these are fit animals who are on high rations. Change in feed rations and boredom encourage them to eat their bedding.
  • Sub-acute grass sickness   Grass sickness  .
  • Infrequent feeding.
  • Damage to colonic nervous system due to previous colonic distention affecting colonic motility.
  • Small colon impactions can occur for the same reasons, but many are idiopathic. Interestingly, one survey showed 25% of those horses that went to surgery for correction of a small colon impaction wereSalmonellapositive.
  • See Rectum: meconium impaction   Rectum: meconium impaction  .

Predisposing factors

  • Recent change in environment or regime.
  • Poor teeth.
  • Inadequate, inappropriate or poor quality feeding.
  • Worms.
  • Lack of sufficient water


  • Inadequately digested food matter (or foreign bodies) accumulates in colon.
  • A blockage of the intestinal lumen results.
  • The impacted ingesta becomes progressively harder and drier with time, and thus more and more solid.
  • Peristaltic waves become weaker due to the presence of a blockage.
  • Dehydration may occur due to decreased eating and drinking.
  • Poorly understood.
  • Impactions tend to occur at sites where there is physical change in:
    EitherThe course of the gut lumen, so a partial 'kink' is present, encouraging ingesta to build up.
    OrSize of gut lumen, ie pelvic flexure and transverse colon.
  • Abnormal gut motility may be as important in the development of this disease as the character of ingesta.
  • Poor GI motility can occur on box rest, since exercise promotes peristaltic activity. Other factors such as lack of fresh grass can be involved.
  • Correlation with presence ofSalmonella  Salmonella spp  may also be associated with that organism's effects on gut motility.


  • Usually a chronic timecourse, involving a gradual build up of the impaction within, and then a gradual worsening of symptoms. If more serious sequele result, the presentation can even appear to be acute.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • McGovern K & Bladon B (2011) Medical management of large colon obstruction in the horse. In Pract 33 (5), 205-208 VetMedResource
  • Monreal L et al (2010) Enteral fluid therapy in 108 horses with large colon impactions and dorsal displacements. Vet Rec 166 (9), 259-263 PubMed.
  • Riley E, Martingale A et al (2007) Small colon lipomatosis resulting in refractory small colon impaction in a Tennessee Walking Horse. Equine Vet Educ 19 (9), 478-481 VetMedResource.
  • Mair T S (2002) Small colon impaction associated with a granulosa cell tumor in a pony mare. Equine Vet Educ 14 (1), 17-18 WileyOnline.
  • Schumacher J & Mair T S (2002) Small colon obstructions in the mature horse. Equine Vet Educ 14 (1), 19-28 VetMedResource.
  • Merritt A M, Burrow J A & Hartless C S (1998) Effect of xylazine, detomidine and a combination of xylazine and butorphanol on equine duodenal motility. Am J Vet Res 59 (5), 619-623 PubMed.
  • Newton S A (1998) Three cases of pelvic flexure impaction in the horse. Equine Vet Educ 10 (6), 284-290 VetMedResource.
  • White N A (1998) Large colon impaction. Equine Vet Educ 10 (6), 291-293 VetMedResource.
  • White N A II & Dabareiner R M (1997) Treatment of impaction colics. Vet Clin North Am Equine Pract 13 (2), 243-259 PubMed.
  • Debarainer R M & White N A II (1995) Large colon impaction in hoses - 147 cases (1985-1991). JAVMA 206 (5), 679-685 PubMed.
  • Proudman C J (1992) A two year, prospective study of equine colic in general practice. Equine Vet J 24 (2), 90-93 PubMed.

Other sources of information

  • Rose R J & Hodgson D R (1993) Manual of Equine Practice. Saunders. ISBN 0 7216 3739 6.