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Colic – Small Intestine

We will continue our series of articles on colic by discussing causes of colic that occur in the small intestine. 

The horse small intestine is over 70 feet in length and contains three parts.  The first part is the duodenum.  It starts at the stomach and extends 3-4 feet.  The second part is the jejunum.  This is the longest section and compromises the majority of the small intestine.  The final section is the ileum, which includes the last 1-2 feet of small intestine.  The ileum is attached to the cecum, which is the first portion of the large intestine and similar to the human appendix1.  There are a variety of problems that can occur in the small intestine and cause colic.  Some of the most common problems are discussed below.

Strangulating lipoma

Strangulating, means that the blood supply to a piece of intestine has been cut off.  With no blood to bring nourishment and oxygen to the cells, the strangulated portion of the small intestine dies.  A lipoma is a small, benign, fatty tumor that develops within the abdomen.  It typically occurs in older horses.  Occasionally the lipoma develops a long string-like stalk.  The lipoma and stalk can wrap tightly around a piece of small intestine, cutting off the blood supply, resulting in death of that section of small intestine.  The amount of affected small intestine can range from a few feet to several dozen feet.  A colic surgery where the dead piece of small intestine is removed and the remaining healthy sections are reconnected is needed if the horse’s life is to be saved. 

Epiploic Foramen Entrapment

The epiploic foramen is a small opening within the upper abdominal cavity located between some of the horse’s largest blood vessels, the vena cava and the portal vein, and the liver1.  Small intestine usually does not move into this small space, but if it does happen to go into this narrow tunnel, it gets stuck (also known as entrapped) and is unable to move out.  Eventually compression within this small space cuts off the blood supply to the affected small intestine and it dies.  Treatment involves surgery where the surgeon gently frees the entrapped or stuck small intestine (remember it is stuck between some really big blood vessels!), removes the dead small intestine, and reconnects the remaining healthy sections.   This type of colic has been associated with horses that crib2.

Small Intestinal Volvulus

The small intestine is attached to the body wall by long, very thin sheets of tissue called mesentery.  Blood vessels that serve the small intestine are contained within the mesentery.  A volvulus occurs when the small intestine and its attached mesentery twist around each other essentially creating a large knot1.  If the twist is tight enough it can result in the blood supply being occluded or cut off to the affected section of small intestine.  Small intestinal volvulus’ treatment requires colic surgery.   During surgery the surgeon detangles the knot of small intestine and evaluates if the affected intestine is viable or not.  If the intestine has died, then removal of the dead section and reconnection of the remaining healthy sections is necessary. 

Anterior Enteritis

Enteritis means intestinal inflammation.  Anterior means front.  Thus anterior enteritis occurs when the small intestine becomes inflamed.  The most commonly affected sections are the duodenum and the beginning of the jejunum, but the entire small intestine can be affected.  The cause of the inflammation is not known1.  Once the small intestine becomes inflamed, it does not function properly to move food and fluid down the GI tract.  The horse’s body continually secretes fluid into the small intestine to help with digestion.  In a normal horse contraction of the small intestine would move this fluid (which would be mixed with food material) down the intestine and it would be re-absorbed in the large intestine.  In horses with anterior enteritis the secreted fluid is not moved through the small intestine and into the cecum.  Instead the fluid backs up in the small intestine, enters the stomach, and must be removed with a nasogastric (stomach) tube.  This excess fluid is called reflux.  Due to this extensive fluid loss, horses with anterior enteritis can rapidly become very dehydrated.  In addition to resulting in lack of function of the small intestine, the inflammation of the intestinal wall leads to the development of endotoxmia.   Horses with anterior enteritis require hospitalization to regularly remove reflux from the stomach and IV fluid therapy to keep them properly hydrated.  In addition treatment also involves anti-inflammatory and anti-endotoxic therapies. 

Ileal Impaction

Ileal impactions occur when partially digested hay builds up in the ileum creating a blockage.  The ileum is the last section of small intestine before the cecum.  Ileal impactions most commonly occur in horses eating Coastal Bermuda grass hay, which is not grown in the Pacific Northwest.  Ileal impactions can also occur in horses with tapeworm infestations3.  Tapeworms attach at the junction of the ileum and cecum and a large infestation can interfere with proper empting of the ileum into the cecum and can result in the development of an ileal impaction.  Many ileal impactions can be resolved with hospitalization, medications to relax the small intestine and control pain, and IV fluid therapy.  Some horses require surgery to have the impaction manually broken down and milked into the cecum.  Tapeworm infestations can be difficult to identify with fecal tests, so all horses should be dewormed once a year with praziquantal, the only deworming medication that kills tapeworms. 

Ascarid Impaction

Ascarids are worms that live in the small intestine.  Adult horses develop a good immunity against ascarids.  As a result they are rarely found in normal horses over a year of age, they are however a problem in foals.  Ascarid impactions typically occur when weanlings that have had minimal parasite control are dewormed. These young horses have developed a large parasite load and deworming them results in widespread die off of the worms.  Masses of dead worms then block and impact the small intestine.   These impactions often require surgery to resolve.  Unfortunately prognosis from surgery for ascarid impactions is often lower than that for other small intestinal surgeries4.  Prevention of ascarid impactions involves routine deworming of young horses.  If a foal’s parasite control therapy has not been optimal, it is important to consult a veterinarian before starting a deworming program as multiple low doses of dewormers may be needed to prevent a massive die off and the development of an impaction. 

The above are just a sampling of some of the more common causes of colic related to the small intestine.   There are a variety of other problems that can occur in the small intestine and cause colic.   As a whole, causes of colic that originate in the small intestine are often serious and in most cases require hospitalization or surgery. 

REFERENCES

  1. Freeman, David.  Small Intestine. Equine Surgery. Ed Auer, AJ, Stick JA. 
  2. Archer DC, Freeman DE, Doyle AJ, et al.  Association between cribbing and entrapment of the small intestine in the epiploic foramen in horses: 68 cases (1991-2002). J Am Vet Med Assoc 224:562, 2004.
  3. Little D, Blikslager AT: Factors associated with development of ileal impaction in horses with surgical colic: 78 cases (1986-2000). Equine Vet J 34:464, 2002. 
  4. Cribb NC, Cote NM, Boure LP, et al: Acute small intestinal obstruction associated with Parascaris equorum infection in young horses: 25 cases (1985-2004). N Z Vet J54:338, 2006.
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