## Overview Large colon volvulus is a twisting of the large colon around the mesentery that connects its dorsal and ventral portions. The large colon is unusually susceptible to this problem because it is long, can hold a large volume of gas and fluid, and has only limited attachments to the body wall. Most of the colon is free to move within the abdomen. When the colon twists, the blood vessels and lymphatic vessels that run in the mesentery become compressed. Depending on the degree of rotation, this can cause simple obstruction of the intestinal lumen or, more seriously, complete strangulation of the blood supply. Large colon volvulus is different from large colon displacement. Displacements (such as left dorsal or right dorsal displacement) move the colon out of its normal position and can obstruct the flow of gas and digesta, but they do not typically cut off the blood supply. Many displacements can be managed with medical therapy or resolve on their own. A true volvulus that compromises blood flow is a strangulating lesion and is always a surgical emergency. ## Causes The exact trigger for large colon volvulus is not fully understood. It is thought to be related to abnormal gas accumulation that makes the colon buoyant and more mobile. Postpartum broodmares are overrepresented in many surgical populations. The increase in free abdominal space after foaling is a plausible contributing factor, but this mechanism has not been directly established. Height and a history of prior colic are supported risk factors. Associations with recent diet or pasture changes have been identified in case-control data, but these are not proven causes. The condition can occur in horses of any age, sex, or breed. ## Diagnosis Your veterinarian will base the initial assessment on the severity and rapidity of the clinical signs. Rectal examination, abdominal ultrasound, blood lactate, and peritoneal fluid analysis can support a suspicion of large colon volvulus. On rectal examination the large colon is often markedly enlarged and the mesentery between the dorsal and ventral portions may feel thickened or edematous. Ultrasound findings of a distended colon with thickened walls or abnormal vessel positioning are suggestive but not definitive. Peripheral lactate is better supported as a prognostic marker reflecting tissue perfusion than as a lesion-specific diagnostic test. Abdominocentesis does not reliably distinguish volvulus from other severe colic lesions. Definitive diagnosis and assessment of bowel viability are usually confirmed at surgery. Stabilization measures such as intravenous fluids, pain medication, and nasogastric decompression support the horse during transport and preparation for surgery, but they do not correct the twist itself. ## Treatment Definitive treatment is emergency surgery. After the horse is anesthetized, the surgeon makes a ventral midline incision, exteriorizes the colon, and derotates it to restore normal positioning and blood flow. The surgeon then evaluates the color, thickness, and motility of the bowel to determine how much tissue is still viable. If a large portion of the colon is necrotic, it may be resected and the healthy ends reconnected (anastomosis). In broodmares with a history of recurrence, some surgeons perform a colopexy (suturing the colon to the body wall) to reduce the chance of future twists. Medical management alone is not a treatment for strangulating large colon volvulus. Pain control and fluid therapy are used only to stabilize the patient for transport and anesthesia. ## Recovery and Prognosis Outcome depends primarily on how long the bowel has been twisted before surgery and on the extent of irreversible damage found at surgery. Some high-volume Thoroughbred broodmare populations report survival to discharge around 88% to 93%, while broader strangulating large colon volvulus cohorts report lower discharge survival around 71% to 77%, with long-term survival lower still. Horses that survive surgery may still face complications such as diarrhea, laminitis, or further colic. Recurrence of large colon volvulus has been reported in approximately 15 percent of cases after one episode, with substantially higher recurrence risk after repeated episodes. ## Prevention There is no proven way to eliminate the risk of large colon volvulus. Practical steps that may reduce risk include making all diet changes gradually and providing close monitoring of broodmares in the late-pregnancy and early-postpartum periods so that colic can be recognized quickly. Owners of horses that have already had one episode of large colon volvulus should discuss the higher recurrence risk and possible preventive surgical options with their veterinarian.
Sudden severe unrelenting abdominal pain that responds poorly to analgesics; rapid heart rate and signs of cardiovascular shock; heavy sweating; progressive abdominal distension; rapid deterioration over hours
## Overview Large colon volvulus is a twisting of the large colon around the mesentery that connects its dorsal and ventral portions. The large colon is unusually susceptible to this problem because it is long, can hold a large volume of gas and fluid, and has only limited attachments to the body wall. Most of the colon is free to move within the abdomen. When the colon twists, the blood vessels and lymphatic vessels that run in the mesentery become compressed. Depending on the degree of rotation, this can cause simple obstruction of the intestinal lumen or, more seriously, complete strangulation of the blood supply. Large colon volvulus is different from large colon displacement. Displacements (such as left dorsal or right dorsal displacement) move the colon out of its normal position and can obstruct the flow of gas and digesta, but they do not typically cut off the blood supply. Many displacements can be managed with medical therapy or resolve on their own. A true volvulus that compromises blood flow is a strangulating lesion and is always a surgical emergency. ## Causes The exact trigger for large colon volvulus is not fully understood. It is thought to be related to abnormal gas accumulation that makes the colon buoyant and more mobile. Postpartum broodmares are overrepresented in many surgical populations. The increase in free abdominal space after foaling is a plausible contributing factor, but this mechanism has not been directly established. Height and a history of prior colic are supported risk factors. Associations with recent diet or pasture changes have been identified in case-control data, but these are not proven causes. The condition can occur in horses of any age, sex, or breed. ## Diagnosis Your veterinarian will base the initial assessment on the severity and rapidity of the clinical signs. Rectal examination, abdominal ultrasound, blood lactate, and peritoneal fluid analysis can support a suspicion of large colon volvulus. On rectal examination the large colon is often markedly enlarged and the mesentery between the dorsal and ventral portions may feel thickened or edematous. Ultrasound findings of a distended colon with thickened walls or abnormal vessel positioning are suggestive but not definitive. Peripheral lactate is better supported as a prognostic marker reflecting tissue perfusion than as a lesion-specific diagnostic test. Abdominocentesis does not reliably distinguish volvulus from other severe colic lesions. Definitive diagnosis and assessment of bowel viability are usually confirmed at surgery. Stabilization measures such as intravenous fluids, pain medication, and nasogastric decompression support the horse during transport and preparation for surgery, but they do not correct the twist itself. ## Treatment Definitive treatment is emergency surgery. After the horse is anesthetized, the surgeon makes a ventral midline incision, exteriorizes the colon, and derotates it to restore normal positioning and blood flow. The surgeon then evaluates the color, thickness, and motility of the bowel to determine how much tissue is still viable. If a large portion of the colon is necrotic, it may be resected and the healthy ends reconnected (anastomosis). In broodmares with a history of recurrence, some surgeons perform a colopexy (suturing the colon to the body wall) to reduce the chance of future twists. Medical management alone is not a treatment for strangulating large colon volvulus. Pain control and fluid therapy are used only to stabilize the patient for transport and anesthesia. ## Recovery and Prognosis Outcome depends primarily on how long the bowel has been twisted before surgery and on the extent of irreversible damage found at surgery. Some high-volume Thoroughbred broodmare populations report survival to discharge around 88% to 93%, while broader strangulating large colon volvulus cohorts report lower discharge survival around 71% to 77%, with long-term survival lower still. Horses that survive surgery may still face complications such as diarrhea, laminitis, or further colic. Recurrence of large colon volvulus has been reported in approximately 15 percent of cases after one episode, with substantially higher recurrence risk after repeated episodes. ## Prevention There is no proven way to eliminate the risk of large colon volvulus. Practical steps that may reduce risk include making all diet changes gradually and providing close monitoring of broodmares in the late-pregnancy and early-postpartum periods so that colic can be recognized quickly. Owners of horses that have already had one episode of large colon volvulus should discuss the higher recurrence risk and possible preventive surgical options with their veterinarian.
Sudden severe unrelenting abdominal pain that responds poorly to analgesics; rapid heart rate and signs of cardiovascular shock; heavy sweating; progressive abdominal distension; rapid deterioration over hours