Approximately 4% horses have a colic episode in a year, with a fatality rate of 11%.
Horses are evolved to graze forage for ~18 hours per day, while constantly moving around. Human management practices affect gastrointestinal physiology for example through stabling and feeding "meals". Furthermore parasite prevalence and resistance can also influence certain types of colic. Management/feeding changes should always be performed gradually.
Horse gastrointestinal anatomy is also not ideal in that it is not well adhered within the abdomen allowing different parts to displace, strangulate or entrap. Coupled with suboptimal management practices, it's almost a surprise horses don't colic more often.
Common types of colic:
- Spasmodic colic: By far the most common type of colic is spasmodic colic, where a section of the gut is spasming or has some gas distension. Luckily many of these resolve with administration of a couple of medications at the yard and do not require follow up visits. However, if the vet is visiting your horse multiple times, there's a good chance they need to be hospitalised for further workup and intesive management.
- Large colon impaction: These most commonly occur where there is narrowing in the colon diameter - the pelvic flexure and between the right dorsal colon and transverse colon. This type of colic can be associated with orthopaedic injuries/exercise restriction, decreased water intake (e.g. in the winter if the water freezes) or poor dentition so the horse is unable to chew it's food properly. Frequently these can be resolved with medical managment and administration of laxatives, but in some cases could require surgery.
- Strangulating lipoma: This type of colic is most common in older horses, particularly in geldings and ponies. A fatty mass on a stalk develops and like a ball on a string wraps around a section of small intestine and tightens until it cuts off the blood supply. Horses that are overweight with an increased body condiiton score tend to have more internal fat deposits and are thought to be more susceptible. These cases always require colic surgery to resolve and more often than not require a resection of a section of small intestine.
- Large colon volvulus ("colon torsion"): This is one of the most severe forms of colic, where the large colon twists around it's own axis, causing a cut off of the blood supply. It is most commonly encountered in post-foaling mares and is one of the most fatal causes of colic. These require rapid referral to colic surgery, however, is often associated with widespread toxin release when the colon is untwisted, causing a host of post-operative complications. In some cases the colon is removed in surgery, which has a poor survival rate in healthy horses, let alone one with a compromised colon.