There are other special circumstances affecting the gastrointestinal (GI) system that can result in impaction of the small or large colon. The formation of fecaliths (a dehydrating and hardening of feces to the extent that it becomes stone-like), enteroliths (a mineral concretion) and meconium-induced impaction (early accumulation of fetal feces in newborns). Horses that have a recent and significant decrease in exercise, usually from an injury, can develop large colon impactions. Twice-daily feedings of grain can result in a measurable increase (up to 15%) in fluids secreted into the bowl from the cardiovascular system which can result in hypotension (reduction of circulating blood volume). This causes the renin-angiotensin-aldosterone regulatory to be activated resulting in the reabsorption of more fluid from the GI tract. This results in a dehydration of the feces and can also result in an impaction.
Four types of displacement colic are described in horses. Displacement occurs because most of the bowel is not anchored to the body wall but suspended from the dorsal abdominal wall in the mesentery. It is therefore relatively easy for a portion to move out of its normal position. Left dorsal displacementoccurs when the pelvic flexure moves toward the space found between the spleen, the left kidney and the nephrosplenic ligament the structure that attaches the spleen and kidneys to the body wall. Right dorsal displacement occurs when the colon lodges between the cecum and the body wall. The pelvic flexure can move to a position closer to the diaphragm resulting in a volvulus, a 180-degree twist along the longitudinal axis. Torsion (a twist along the axis of the mesentery) can also occur. The mesentery is the diaphanous tissue supporting the bowel through which veins, arteries and nerves are carried from the dorsal abdominal wall to the intestine.
Any type of displacement can result in an occlusion of the blood supply (partial or complete) to the involved portion of the GI tract.
Left dorsal displacement will often resolve itself following conservative medical treatment. In recalcitrant cases your veterinarian may elect to anesthetize the horse, put it on its left side, then quickly roll it to its right side while repeatedly pushing on the abdomen. Obviously, this is not a maneuver to be attempted by only one person.
An intussusception of the bowel occurs when a section of intestine “telescopes” into an adjacent section. This most often occurs at the ileocecal junction. When this happens, surgical correction is the only effective treatment. This condition is most common in horses about one year old and is almost always associated with tapeworms, other parasites, small masses and foreign bodies or severe diarrhea.
Epiploic foramen entrapment occurs when a portion of the small intestine (rarely the colon) becomes lodged in the epiploic foramen, also known at the foramen of Winslow. This opening is the communication between the abdominal cavity and the omental bursa. Entrapment of a loop of bowel can also occur through a rent (tear) in the mesentery.
Proximal enteritis (inflammation of the gut lining) is usually the result of infectious organisms, particularly Salmonella and/orClostridium species. Fusarium(a large genus of filamentous fungi) can also be the cause of enteritis. Fusariuminfections occur most commonly in the Southeastern U.S. Overfeeding a high concentrate diet can also result in enteritis. Horses suffering from enteritis have an increased risk of laminitis and thrombophlebitis. Colitis (inflammation of the lining of the colon) is most often associated with infectious caused by Salmonella species, Clostridium difficileand/or Neorickettsia risticii. This last organism is the cause of Potomac Horse Fever. Ingestion of toxic agents such as arsenic or cantharidin, as well as several plant toxins can result in colitis as well.
Gastric ulceration is associated with confinement (lack of adequate exercise), infrequent feeding, a high concentrate diet, over-use of non-steroidal anti-inflammatory (NSAID) drugs, and from the stress associated with shipping and/or performing.
Tumors that can affect the GI tract and result in colic include lipomas (fatty tumors) that form on the mesentery and stretch the connective tissue into a stalk as it enlarges. The stalk can wrap around a section of bowel, usually the small intestine. Neoplastic growths of the GI tract can also include lymphosarcoma, leiomyomas, adenocarcinomas and squamous cell carcinomas. The last of these usually involves the stomach.
Ileus is characterized by no, or very low, movement of the intestines. Between ten and fifty percent of horses will develop ileus following abdominal surgery, with over 80% of those animals having been operated on for correction of a strangulating obstruction. Diagnosis is made using ultrasound when more than three loops of intestine lack peristaltic waves.
Hernias can result in incorporation of a loop of bowel and signs of colic. Standardbred and Tennessee Walker stallions are prone to a large inguinal ring and inguinal hernias. Umbilical and diaphragmatic hernias are rare but can occur in any breed of horses.
Non-bowel related colic include the ingestion of toxins, uterine tears and torsions, disease of the liver, ovaries, spleen, urinary system, or testicular torsion. Inflammatory conditions of the pleura (lining of the lungs and thorax), uterine contractions, laminitis and rhabdomyolysis can all present with signs resembling colic.
Parasitic infestations with Parascaris equorum(roundworms), Anoplocephala perfoliate(tapeworms), cyathostomes(Strongylus-type roundworms) and Strongylus vulgariscan all result in colic. The larvae of Strongylusspecies migrate out of the GI system and find their way into the arterial system. They are sometimes found in the cranial mesenteric artery where they can cause vasospasm as well as blockage. The regular use of modern anthelminthics has reduced the incidence of this problem.