Transcript:

[0:00]

Hi everyone, welcome back to Mad Barn Academy, and thanks for tuning in. For those of you who are new here today, we hope to earn your subscription — the ongoing support means the world to us — so like and subscribe. I’m Dr. Fran Row, one of the veterinary nutritionists here at Mad Barn. Today I’m going to be discussing a topic that’s particularly relevant for this time of year for horse owners: impaction colic, and specifically large colon impactions. So let’s get started.

[0:30]

Firstly, let’s discuss impactions in general. Impactions are a type of colic in which the bowel becomes obstructed by either digesta that’s dry or firm masses of feed, or potentially some type of foreign material like sand, parasites — specifically roundworms — enteroliths, or other foreign bodies. Impactions can occur anywhere along the GI tract, but the most common location, likely across most populations of horses and most regions, is the large colon.

[1:14]

To quickly review the movement of digesta through the gastrointestinal tract: the horse eats, swallows, and digesta moves from the stomach, through the small intestine, into the cecum, out of the cecum into the large colon, through the entire large colon, then through the small colon, and finally out the rectum.

[1:55]

Normally, peristalsis — the smooth muscle contractions of the gut — push digesta in the aborad direction, meaning away from the mouth toward the rectum. However, there are a couple of locations in the GI tract where smooth muscle contractions differ from this typical one-directional movement. The cecum is a good example — digesta must enter and exit through the same orifice, and it has to travel through the entire cecum, down and back.

[2:41]

When we have an impaction somewhere along the GI tract, it blocks the normal movement of digesta. This causes gas and fluid buildup behind the impaction, which will eventually cause enough distension to be painful — that’s when we see signs of colic. Additionally, the impaction will start to cause pressure necrosis in the gut wall if it gets big enough and sits there long enough. Compromise to the gut wall increases the risk of bacteria leaking from the gut into the bloodstream (endotoxemia) and even the risk of gut rupture.

[3:31]

So, what makes the large colon so special in terms of developing impactions? The biggest factor is that the large colon undergoes two drastic changes in diameter — quite large to quite narrow — in two specific spots, which are perfect places for things to get stuck. These two locations are the pelvic flexure (the junction between the left ventral colon and left dorsal colon) and the transverse colon (a very short section between the right dorsal colon and the small colon).

[4:22]

Additionally, there are unique contraction patterns at these locations that can exacerbate impaction formation. At both spots, there are retropulsive — or backwards — contractions that slow the movement of digesta. We believe this enhances microbial digestion at these locations. Together, these areas create a bottleneck with slower motility, making it the perfect spot for dry feed or other material to build up and impact.

[5:06]

Our understanding of large colon impactions hasn’t changed much in the last 30 to 50 years, meaning we have a thorough understanding of causes, diagnosis, treatment, and importantly, prevention. To illustrate this, I pulled two articles separated by about 20 years.

[5:39]

The first, a 1995 retrospective study from the Marion duPont Scott Equine Medical Center, looked at large colon impaction cases. About 88% of cases were referred by the primary vet for additional workup and treatment; 12% developed an impaction during hospitalization for unrelated reasons, such as musculoskeletal injury. The prognosis was quite good — most cases were successfully treated medically, with a smaller number requiring surgery. Long-term survival was excellent for medically treated horses, and still quite good for surgical cases. Over half of cases had a recent change in routine within two weeks, most commonly exercise restriction or stall rest.

[7:12]

The second, a 2014 prospective survey, assessed veterinarians’ experiences with large colon impactions. The findings were very similar — prognosis remained very good, with most horses treated successfully with medical management. Again, over half had a recent management change, like diet change, stall rest, or more time stalled. The majority occurred in winter, which aligns with what many of us recognize anecdotally.

[8:19]

The biggest takeaway? Most large colon impactions are related to management changes, meaning they’re preventable if we’re careful. Change is inevitable — our day-to-day horse management shifts with the seasons — but we can manage those changes wisely.

[8:51]

Impactions occur due to a combination of altered GI motility and dry digesta or foreign material. It can be a chicken-or-egg situation: did motility slow first, or did digesta dry out first? Either way, these two factors exacerbate each other and can snowball into a full-blown impaction.

[9:27]

Factors that predispose to decreased motility and/or dry digesta include poor dentition, ingestion of coarse roughage (poor quality, stemmy hay or straw), inadequate water intake, stress (trailering, environmental changes), changes in activity (increased stall rest, reduced turnout), and exercise level changes (either much more or much less exercise).

[10:23]

In winter, three management changes make impactions more common: changes in forage (transition from pasture to hay-only diet, switching to a new batch of hay), changes in drinking behavior (reluctance to drink cold water, frozen buckets or troughs), and changes in activity (off-season, less exercise, more time stalled or standing due to weather).

[11:36]

To reduce winter impaction risk:
— For forage, avoid coarse, stemmy, poorly digestible hay if possible. If unavoidable, supplement with more digestible feedstuffs like soaked forage cubes or pellets, beet pulp, or rice bran. Don’t neglect dental exams, especially for seniors.
— For hydration, monitor water intake, use heaters or heated buckets, prevent ice formation, and add salt or electrolytes (1–2 tablespoons plain salt daily for an average 1100 lb/500 kg horse) to encourage drinking.
— For activity, encourage movement to promote GI motility. Regular exercise and turnout are important. For outdoor-kept horses, place feeding stations and water apart to promote movement.

[13:51]

Signs to watch for: mild discomfort (unless severe or complicated), changes in attitude, lethargy, reduced appetite, reduced manure output, small hard fecal balls, mucus-covered manure, flank-watching, stretching, lying down more, tacky mucous membranes with delayed capillary refill, and reduced or absent gut sounds.

[15:22]

All right — references for today, and thanks for listening. I hope you found this presentation helpful and now have a better understanding of large colon impactions. If you liked today’s discussion, like and subscribe, and check back for new videos. Until next time, thanks!