Good hydration can not only prevent impactions but also help resolve them. | Photo: Alexandra Beckstett/The Horse

When temperatures drop in the winter, impaction of the large colon becomes a common cause for emergency farm calls. Impaction colic occurs when digested material within the large colon becomes stuck. Because the material stays in one place, the large colon absorbs moisture from it, generating a doughy to hard, dry mass. Impactions commonly occur where the large colon narrows and turns at the pelvic flexure.

Causes often associated with impactions include decreased water consumption and changes in routine. In the winter when the weather changes, especially abruptly, horses might have reduced turnout and exercise and might not be interested in drinking, particularly if the water is very cold. Other causes of impaction can be related to the inability to chew and break down feed well (e.g., due to pain or poor dentition), an abnormality in the gastrointestinal (GI) tract (e.g., a tumor), or a problem with the GI tract’s ability to move digesta efficiently and effectively—called motility.

With an impaction blocking newly ingested material, the horse stops passing manure, could exhibit mild to severe signs of abdominal discomfort, and might or might not show a decrease in appetite. It’s possible on physical exam that your veterinarian will find signs of dehydration (tacky gums and skin that returns to normal slowly when pinched during a skin tent test) and decreased gut sounds. Rectal palpation often allows the veterinarian to confirm and characterize an impaction at the pelvic flexure. On some occasions an impaction of the large colon can be out of reach during a rectal exam. In these cases a veterinarian might decide to treat for an impaction, while also ruling in or out other causes of colic (sometimes impaction can precede serious colics with intestinal