Intestinal obstructions are functional or mechanical in nature and result in a decrease or absence of feces. Diagnosis is on the basis of abnormal findings during examination via palpation per rectum, transcutaneous ultrasonography, clinicopathological testing (including peritoneal fluid analysis), and exploratory laparotomy. Treatment depends on the cause of the obstruction.
Intestinal obstructions occur in all large animal species; however, they are most common in horses. Cattle are the most commonly affected ruminants; sheep and goats are rarely affected, except for intestinal volvulus in lambs. Pigs can also experience intestinal obstructions, in addition to inguinal hernias.
Because of their indiscriminate eating practices, pet pigs are at greater risk of foreign body intestinal obstruction than commercial pigs (1, 2).
Obstructions interrupt the flow of ingesta and can be mechanical or functional in nature. Mechanical intestinal obstructions are characterized as being luminal or extraluminal. Extraluminal obstructions include strangulating obstructions in animals with volvulus of a portion of the GI tract or simple extraluminal obstruction in animals with an abdominal mass, such as lymphosarcoma or fat necrosis in cattle or strangulating lipomas in horses.
Functional obstructions, characterized by generalized hypomotility or ileus, can occur spontaneously secondary to inflammation, pain, or infectious agents. In general, functional obstructions occur more often than mechanical obstructions, and ileus is commonly encountered in horses and pigs after abdominal surgery.
Etiology and Pathogenesis of Acute Intestinal Obstructions in Large Animals
Mechanical obstructions (physical blockage of ingesta) occur because of abnormalities in the bowel lumen or bowel wall or because of obstructions external to the GI tract. These can include congenital obstructions (eg, atresia jejuni, coli, recti, and ani in calves; atresia ani in lambs and pigs) that block the passage of feces from birth. Atresia coli develops most commonly in Holstein-Friesian calves secondary to in utero ischemia of the developing spiral colon.
In contrast, functional obstructions are associated with altered intestinal motility as the result of infection, electrolyte abnormalities, or genetic defects. Functional obstructions can also be related to congenital motility disorders such as megacolon (intestinal aganglionosis) in foals with lethal white foal syndrome or a mutation in the endothelin type B receptor gene that causes lack of passage of feces from birth in Cameroon lambs.
In horses, transient functional obstructions are common, as are true mechanical obstructions such as feed impactions, which usually involve the pelvic flexure of the large colon. Parasite infection or migration (see and images), dental abnormalities, and dietary or management factors (eg, poor water quality, sand ingestion related to feeding from the ground, feeding of poor-quality hay) are often implicated in the development of intestinal obstructions.
Functional obstruction of the jejunum in a yearling equine secondary to an ascarid (Parascaris equorum) impaction. Note the worms can be observed through the intestinal wall.
Courtesy of Jennifer Schleining and Eric Reinertson.
Functional obstruction of the jejunum in a yearling equine secondary to an ascarid (Parascaris equorum) impaction requiring surgical removal.
Courtesy of Jennifer Schleining and Eric Reinertson.
Impactions and other luminal obstructions can result from coarse feeds, decreased 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, ileum, and less commonly the stomach. Intussusceptions are thought to be the result of irregular peristaltic movements related to enteritis, intestinal parasitism, dietary disorders, and mural masses.
Other causes of extraluminal intestinal obstruction in horses are volvulus (twist on the mesenteric axis) or displacement of the large colon and volvulus of part or all of the small intestine. Altered motility and possibly strenuous exercise and rolling can be initiating causes in horses.
Broodmares can be predisposed to volvulus or displacement of the large colon during gestation and shortly after parturition.
Altered intestinal motility related to ingestion of a rapidly fermentable substrate can also cause intestinal volvulus. In cattle, decreased motility caused by accumulation of volatile fatty acids, possibly related to feeding of high-concentrate rations or an abrupt increase in the concentrate-to-forage ratio, have been suggested as causes of cecocolic volvulus (3). Cecocolic volvulus can also occur in association with or because of advanced pregnancy or ileus from another condition.
Obstructions of the small intestine can develop because of:
incarceration
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, diaphragmatic, or umbilical)
intussusception of the jejunum and ileum
Obstruction related to incarceration of the intestine occurs by herniation of the bowel through the inguinal canal, the diaphragm, a mesenteric defect, the umbilicus, or the epiploic foramen (in horses). It can also occur with strangulations, rents, or adhesions associated with the omentum or because of fibrous bands such as mesodiverticular bands or stalks of pedunculated lipomas.Adhesions, abdominal abscesses, or tumors can also create obstructions in adjacent bowel (4).
Standardbred stallions and colts develop inguinal and scrotal hernias more commonly than other breeds. Diaphragmatic hernias and mesenteric defects can be congenital or traumatically induced.
In cattle, causes of intestinal obstruction include:
volvulus of the duodenal sigmoid flexure
volvulus of the jejunoileal flange of the small intestine (see )
luminal occlusion of the jejunum because of a blood clot secondary to jejunal hemorrhage syndrome
obstruction of the small intestine or spiral colon by a phytobezoar
cecocolic volvulus
atresia coli, recti, and ani
mesenteric fat necrosis
Mechanical obstruction of the small intestine secondary to a volvulus of the jejunoileal flange in a mixed-breed beef cow, necessitating resection and anastomosis.
Courtesy of Jennifer Schleining and James Thompson.
Clinical Findings and Diagnosis of Acute Intestinal Obstructions in Large Animals
Decreased or absent feces
Variable abdominal distention
Abdominal pain
Dilated bowel loops on rectal palpation or transabdominal ultrasonography
Intestinal obstruction in horses generally manifests as abdominal pain with restlessness, rolling, pawing, and kicking at the abdomen. These clinical signs are referred to as "colic." For additional information on findings and diagnosis of intestinal obstruction in horses, see Overview of Colic in Horses.
In cattle, clinical signs of abdominal pain potentially associated with intestinal obstruction include treading of the hindlimbs, stretching, restlessness, kicking at the abdomen, and grinding of teeth; rolling and bellowing rarely occur (see ). 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 in cattle are relatively consistent but can sometimes be transient (eg, with some intussusceptions and some cases of cecocolic volvulus). Root-of-mesentery volvulus is typically the most painful and clinically compromising volvulus in cattle. Volvulus of the jejunoileal flange and volvulus at the root of the mesentery are characterized by acute onset and rapid cardiovascular deterioration.
Cattle with intestinal obstruction are generally anorectic and pass few or no feces, and milk production in lactating cows drops suddenly. Passed feces can be covered with mucus or mixed with or coated with blood. Thick, raspberry-colored blood mixed with scant feces is characteristic of small intestinal bleeding, particularly that associated with intussusception or jejunal hemorrhagic syndrome.
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.)
In cattle with cecocolic volvulus, abdominal distention occurs and is usually associated with a tympanic resonance ("ping") on simultaneous auscultation and percussion in the upper right caudal abdominal quadrant. Cecal dilatation does not produce abdominal distention; however, a ping is generally present in the caudal dorsal right 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. Metabolic and cardiovascular derangement tend to be mild except in cecocolic volvulus of long duration.
Abdominal distention in the lower right abdominal quadrant in cattle sometimes occurs along with small intestinal distention. Distended loops of small intestine can be palpable on rectal examination, and fluid can be heard on simultaneous ballottement and auscultation of the right side of the abdomen. Small areas of tympanic resonance can be heard on simultaneous auscultation and percussion.
Intussusceptions and fibrous bands that cause small intestinal obstruction in cattle can sometimes be palpated per rectum. Ultrasonographic examination of the abdomen via the right paralumbar fossa or per rectum can help identify the presence of small intestinal distention, ileus, hypomotility or atony, and 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 strangulating obstructions, regardless of species.
In ruminants, metabolic derangements range from hypokalemic, hypochloremic metabolic alkalosis in long-standing small intestinal and abomasal obstructions to severe metabolic acidosis with strangulating obstructions. There are typically no metabolic derangements in mild functional obstructions or early (simple) mechanical obstructions, particularly if a relatively distal portion of the intestinal tract is involved. Hypocalcemia can be present as a contributor to primary functional obstruction or as a sequela from an obstruction, presumably because of decreased calcium absorption from the duodenum.
Peritoneal fluid changes reflect the extent of peritonitis and can aid in the diagnosis of intestinal obstruction in both cattle and horses. These can be summarized as follows:
Increases in values of peritoneal lactate, total protein, and nucleated cell count, as well as a decrease in peritoneal glucose concentration, can be useful in determining intestinal compromise or peritonitis.
Strangulating obstructions are characterized by increased concentrations of total protein, lactate, and nucleated cells.
Peritoneal fluid analysis is normal with most simple mechanical and functional obstructions.
Plant material in the peritoneal cavity is indicative of bowel rupture or inadvertent enterocentesis.
Treatment of Acute Intestinal Obstructions in Large Animals
Usually medical in functional obstructions
Usually 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 supportive and administered according to the clinical signs 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 IV).
Lactating cows with functional intestinal obstruction 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 intervals) (5).Secondary ketosis should be treated with the administration of propylene glycol and nutritional support if present.
Studies documenting the efficacy of prokinetics in ruminants with small or large intestinal obstruction are lacking. Prokinetic 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 resolved.
Pearls & Pitfalls
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Mechanical obstructions almost always require surgery.Antimicrobial treatment should be started preoperatively, and supportive treatment, such as fluids, electrolytes, and calcium, should be administered as needed.
In horses that require exploratory laparotomy to correct an intestinal obstruction, the survival rate is considerably affected by time to referral (6). 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, the prognosis for cecocolic volvulus is generally good with early intervention, although a small number of cases can recur.
For cows with small intestinal obstruction, prognosis is guarded after resection and anastomosis (7, 8).
For cows with volvulus of the jejunoileal flange of the small intestine or at the root of the mesentery, survival ranges from 23% to 86% if surgical correction is performed within a few hours after onset (9, 10, 11). For dairy cows with volvulus of the duodenal sigmoid flexure, 75% survived to discharge after surgical correction (12). In another study reporting the outcome of spiral colon torsion in cattle, 45% survived (13).
Less than 30% of calves with atresia coli survive to adulthood (14, 15). Surgical correction of atresia coli is not recommended in Holstein-Friesian calves, because the condition is probably inherited in this breed.
Prevention of Acute Intestinal Obstructions in Large Animals
Prevention of 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 are all risk factors for intestinal obstruction and should be avoided or corrected.
Key Points
Intestinal obstructions are functional or mechanical in nature.
Functional obstructions are usually treated medically.
Mechanical obstructions typically require surgical correction.
For More Information
Freeman DE. Fifty Years of Colic Surgery. Equine Vet J. 2018;50(4):423-435.
Desrochers A, Anderson DE. Intestinal surgery. Vet Clin North Am Food Anim Pract. 2016;32(3):645-671.
Meylan M. Surgery of the bovine large intestine. Vet Clin North Am Food Anim Pract. 2008;24(3):479-496.
Also see pet owner content regarding GI obstruction in horses.
References
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