Acute Intestinal Obstructions in Large Animals

The inciting cause of a functional intestinal obstruction often is not determined. Functional obstructions are associated with altered intestinal motility, often due to dietary or management factors, phytobezoars, parasitic infection, enteritis, peritonitis, or electrolyte abnormalities. Functional obstructions may also be due to congenital motility disorders such as megacolon (intestinal aganglionosis) in foals with lethal white foal syndrome and the result of a mutation in the endothelin type B receptor gene that causes lack of passage of feces from birth in Cameroon lambs. Mechanical obstructions (physical blockage of ingesta) occur because of abnormalities in the bowel lumen, bowel wall, or obstructions external to the GI tract. Mechanical obstructions include congenital obstructions (e.g., atresia jejuni, coli, recti, and ani in calves; atresia ani in lambs and pigs) that block the passage of feces from birth.

In horses, transient functional obstructions are common, as are feed impactions, which usually involve the pelvic flexure of the large colon. Parasite infection or migration, dental abnormalities, and dietary or management factors (e.g., poor water quality, sand ingestion due to feeding from the ground, feeding of poor-quality hay) are often implicated in the development of functional obstructions. Impactions and other luminal obstructions can result from coarse feeds, reduced water intake, enteroliths, or ingestion of foreign material. Common sites of impaction other than the pelvic flexure are the small colon, transverse colon, right dorsal colon, cecum, and ileum.

Other causes of intestinal obstruction in horses are volvulus (twist on the mesenteric axis), torsion (twist along the long axis of the bowel), displacement of the ascending (large) colon, and volvulus of part or all of the small intestine. Altered motility and possibly strenuous exercise and rolling may be initiating causes. Broodmares may be predisposed to volvulus, torsion, or displacement of the ascending colon during gestation and shortly after parturition. Obstruction occurs either because of incarceration of the intestine (usually small) by herniation through the inguinal canal, diaphragm, mesenteric defects, umbilicus, or epiploic foramen; or because of fibrous bands (adhesions, mesodiverticular bands, or stalks of pedunculated lipomas). Standardbred stallions and colts develop inguinal and scrotal hernias more commonly than other breeds. Diaphragmatic hernias and mesenteric defects may be congenital or traumatically induced. Adhesions in horses are most often the sequela of parasite migration or abdominal surgery; however, most adhesions are clinically silent. Pedunculated lipomas are common in older horses. Ileocecal, cecocecal, cecocolic, and small-intestinal intussusceptions also occur. Lymphosarcoma and other abdominal neoplasms, as well as abdominal abscesses, can cause intestinal obstruction.

In cattle, specific causes of intestinal obstruction include:

• Volvulus of the duodenal sigmoid flexure

• Intussusception of the jejunum and ileum

• Volvulus of the jejunoileal flange of the small intestine

• Volvulus at the root of the mesentery

• Luminal occlusion of the jejunum due to a blood clot secondary to hemorrhagic jejunitis

• Obstruction of the small intestine or spiral colon due to phytobezoar

• Cecocolic volvulus

• Atresia coli, recti, and ani

Intussusceptions are thought to be the result of irregular peristaltic movements related to enteritis, intestinal parasitism, dietary disorders, and mural masses. Altered intestinal motility due to ingestion of a rapidly fermentable substrate may cause intestinal volvulus.

Obstructions of the small intestine can develop because of:

• Presence of fibrous bands (eg, adhesions, parovarian bands, falciform ligament, spermatic cord retraction into the abdomen after surgical castration)

• Mural thickening (eg, intestinal adenocarcinoma)

• Extramural masses (eg, lymphosarcoma, fat necrosis, abdominal abscesses)

• Herniation (omental, inguinal, or umbilical)

• Hemorrhagic jejunitis (which results in luminal blood clots and obstruction)

Adhesions and abdominal abscesses can form subsequent to peritonitis, intraperitoneal injections, or previous abdominal surgery. Decreased motility caused by accumulation of volatile fatty acids, possibly related to feeding of high-concentrate rations or an abrupt increase in the concentrate:forage ratio, have been suggested as causes of cecocolic volvulus in cattle. Cecocolic volvulus also can occur in association with or due to advanced pregnancy or ileus from another condition. Atresia coli develops most commonly in Holstein-Friesian calves secondary to in utero ischemia of the developing spiral colon.

• Decreased or absent feces and variable abdominal distention

• Presence of abnormalities during palpation per rectum, transcutaneous ultrasonography, clinicopathologic and peritoneal fluid analysis, and exploratory laparotomy

Intestinal obstruction in horses generally manifests as abdominal pain, with restlessness, rolling, pawing, and kicking at the abdomen, and is termed colic. In cattle, clinical signs of abdominal pain include treading of the hind limbs, stretching, restlessness, kicking at the abdomen, and grinding of teeth; rolling and bellowing rarely occur. Clinical signs of intestinal obstruction in cattle are generally more subtle than in horses and are usually referable to small-intestinal distention, tension on the intestinal mesentery (by the weight of distended bowel), or vascular impairment. Clinical signs of pain are relatively consistent but often transient with intussusceptions and occur in some cases of cecocolic volvulus. Cattle with volvulus of the small intestine at the root of the mesentery are severely affected.

Usually, cattle with intestinal obstruction are anorectic and pass few or no feces, and milk production in lactating cows drops suddenly. Passed feces may be covered with mucus, or mixed or coated with blood. Thick, raspberry-colored blood mixed with scant feces is characteristic of small-intestinal bleeding, particularly that associated with intussusception or hemorrhagic jejunitis. Blood from the colon or rectum is generally brighter red. Melena is typical of abomasal bleeding. Calves with atresia coli are healthy at birth; however, they have progressive abdominal distention and decreased appetite during the first few days of life. (Also see Congenital and Inherited Anomalies Involving the Digestive System.)

Abdominal distention, usually with a tympanic resonance ("ping") on simultaneous auscultation and percussion, in the upper right caudal abdominal quadrant occurs with cecocolic volvulus. Cecal dilatation does not produce abdominal distention; however, a ping is generally present in the caudal dorsal paralumbar fossa. In cecocolic volvulus, one or more large, distended loops of large intestine are identified on palpation per rectum. Rumen hypomotility is usually present, and metabolic and cardiovascular derangement tend to be mild except in cecocolic volvulus of long duration.

Abdominal distention in the lower right abdominal quadrant sometimes occurs along with small-intestinal distention. Distended loops of bowel may be palpable on rectal examination, and fluid may be heard on simultaneous ballottement and auscultation of the right side of the abdomen. Small areas of tympanic resonance may be heard on simultaneous auscultation and percussion. Intussusceptions and fibrous bands that cause small-intestinal obstruction can be palpated per rectum in ~25% of cases. Ultrasonographic examination of the abdomen via the right paralumbar fossa or per rectum may help identify the presence of small-intestinal distention, ileus, hypomotility or atony, and an increased peritoneal fluid volume. Occasionally, ultrasonography can identify an intussusception.

Profound changes in cardiovascular parameters, such as tachycardia, abnormal color of the mucous membranes, prolonged capillary refill time, and dehydration, are most commonly associated with hemorrhagic strangulating obstructions such as volvulus of the jejunal-ileal flange of the small intestine. Volvulus of the jejunal-ileal flange and volvulus at the root of the mesentery are characterized by acute onset and rapid cardiovascular deterioration. This is in contrast with cecocolic volvulus or intussusception, which can continue for several days in cattle.

Metabolic derangements range from hypokalemic, hypochloremic metabolic alkalosis in longstanding small-intestinal and duodenal obstructions to severe metabolic acidosis with strangulating obstructions. Usually, there are no metabolic derangements in mild functional obstructions and early (simple) mechanical obstructions, particularly if a relatively distal portion of the intestinal tract is involved. Hypocalcemia can develop, presumably because of decreased calcium absorption from the duodenum.

Peritoneal fluid changes reflect the extent of peritonitis and may aid in the diagnosis in both cattle and horses, although results are more variable in cattle. Strangulating obstructions are characterized by an increase in the total protein concentration and nucleated cell counts of peritoneal fluid due to extravasation through the bowel wall. Neutrophils become degenerative, and intracellular gram-positive and gram-negative bacteria are seen in peritoneal fluid as the integrity of the bowel wall is lost. Plant material in the peritoneal cavity is indicative of bowel rupture or inadvertent enterocentesis. Peritoneal fluid analysis is normal with most simple mechanical and functional obstructions. When neoplasms are present and causing an extraluminal obstruction, neoplastic cells are sometimes identified in peritoneal fluid samples.

• Based on the cause of the obstruction

• Usually medical in functional obstructions and surgical in mechanical obstructions

For treatment of intestinal obstruction in horses, see Overview of Colic in Horses. Treatment of functional intestinal obstruction in cattle is generally symptomatic and supportive after identifying and eliminating the inciting cause (eg, hypocalcemia, hypokalemia, excessive grain intake) and allowing time for normal intestinal motility to return. If present, dehydration and electrolyte imbalances should be corrected by appropriate fluid therapy (oral or intravenous). Lactating cows often benefit from calcium chloride gels administered orally or calcium borogluconate or calcium gluconate administered subcutaneously, and oral potassium chloride (120 g twice at 12-hour interval). Secondary ketosis should be treated if present.

Erythromycin (10 mg/kg, IM, every 12 hours) is the most effective pharmacologic method purported to increase abomasal emptying rate in cattle (and presumably increasing intestinal motility); however, studies documenting efficacy in functional intestinal obstruction are lacking. Prokinetics agents should not be administered to cattle with a mechanical obstruction because of the increased risk of intestinal rupture proximal to the obstruction. The prognosis with most functional obstructions is good with appropriate supportive therapy, particularly if the inciting cause is identified and eliminated.

Mechanical obstructions almost always require surgery. Antimicrobial treatment should be started preoperatively; supportive treatment, such as fluids, electrolytes, and calcium, should be administered as needed.

In horses that require exploratory laparotomy to correct an intestinal obstruction survival rate is considerably affected by time to referral and surgeon experience and training. The survival rate is lower for horses with strangulating obstructions and small-intestinal lesions than for horses with simple obstructions; early surgical intervention improves the prognosis.

In cattle, 70%–80% of those with cecocolic volvulus survive, although 10% of cases recur. For cows with small-intestinal obstruction amenable to resection and anastomosis, 30%–40% survive and lead a productive life. For cows with volvulus of the jejunal-ileal flange of the small intestine or at the root of the mesentery, ~50% survive if surgical correction is performed within a few hours of onset. Less than 30% of calves with atresia coli survive to adulthood. Surgical correction of atresia coli is not recommended in Holstein-Friesian calves because the condition is probably inherited in this breed, although vascular damage secondary to amniotic vesicle palpation in the first 6 weeks of embryonic development can also lead to intestinal ischemia and atresia in calves.

Prevention of all, or even most, cases of intestinal obstruction is not possible. However, abrupt changes in feeding and management; inadequate water intake; parasite infection; dental abnormalities; and access to coarse feeds, highly fermentable feedstuffs, and foreign material should be avoided or corrected.

• Freeman DE. Fifty Years of Colic Surgery. Eq Vet J. 2018. 50:4;423-435.

• Also see pet health content regarding GI obstruction in horses.