Small intestinal lesions

Predispositions to disease

The long jejunal mesentery allows movement; this means the jejunum can twist upon self or herniate through other spaces (inguinal rings, mesenteric rents, etc)

Horses can live without approximately 50% of SI; if >50% removed, they often have inadequate digestion of nutrients. Horses with >50% of the SI damaged are usually euthanized at surgery

Clinical signs

The small intestine is covered by the rib cage so small intestinal distension is usually not noticeable externally. Due to their small size, intestinal distension may be visible in foals (you can see evidence of distended loops of SI in the flank).

Pain is observed if there is intestinal distension, mesenteric traction, and/or inflammation. Depression is seen if the horse has peritonitis, enteritis, and/or dead intestine.

Reflux

If a small intestinal  obstruction is present, the horse will reflux eventually. How fast this happens depends on how far downstream the obstruction is and how dehydrated the horse is.

It is possible to have functional obstructions – no physical obstruction exists but ingesta doesn’t move downstream due to motility disorders. These will also reflux.

Rare large intestine disorders can lead to reflux.

Hypovolemic and/ or endotoxic shock

Signs include tachycardia, weak pulses and prolonged CRT. Severe tachycardia is usually due to shock and the need to move the blood back to the heart as fast as possible vs due to pain.

Horses are very sensitive to low levels of endotoxin! When toxic, they can also develop toxic (darker) lines around the teeth or purplish mucous membranes.

Significant electrolyte abnormalities

Electrolyte disorders with SI lesions are due to secretory and absorption function of the small intestine.

Secretions are usually increased if an obstruction is present– the body tries to hydrate it and break it down. These secretions carry high levels of electrolytes. If the secretions can’t move downstream, they can’t be reabsorbed.

Re-absorption can be hampered if the intestinal wall is swollen or contains inflammatory cells. These changes increase the distance to the capillaries and lymphatics, interfering with absorption of nutrients.

Rectal examination

Small intestine is not normally palpable on rectal examination. Due to the size of the equine abdomen, distended small intestine may still not be palpable in the horse. The ileocecal area should be palpable on the cranial right aspect (per rectum) if the ileum is distended.

Ultrasound examination

Ultrasound allows the examiner to check most of the abdomen for distended SI. Small intestine is generally not visible ultrasonographically in healthy, fed horses. You can see small intestine in horses that are off feed but it should be flaccid in the inguinal area. Distended small intestine on ultrasound is never normal. Poor motility can be seen with both ileus cases and with obstruction. Thickened intestinal wall can be seen with edema (low protein, twists impairing venous return) and with infiltrates (wbcs, neoplasia)