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Internal entrapments in horses describe cases where a segment of the small intestine gets trapped in other structures within the abdominal cavity. This can lead to serious complications, including obstruction of the digestive tract and potentially disruption of blood flow to the intestine.

Interruption of intestinal blood supply can lead to tissue death, causing severe damage or even death. Different types of entrapments can occur in various locations within the abdominal cavity, such as mesenteric rent entrapment, epiploic foramen entrapment, gastrosplenic entrapment, and nephrosplenic entrapment.

These conditions often present with symptoms of colic in horses and require prompt veterinary attention. The causes are not fully understood, and risk factors and diagnostic methods vary between the specific entrapments.

Early detection and surgical intervention improve the horse’s prognosis and help prevent severe complications. Read on to learn more about equine entrapments so you are prepared if one of your horses develops this condition.

Internal Entrapments in Horses

Internal entrapment in a horse refers to conditions where a segment of the small intestine becomes trapped within other structures inside the abdomen.

This disrupts the normal flow of food, gas, and fluids through the digestive tract. In severe cases, blood flow to the intestine is cut off, leading to eventual tissue death (necrosis).

Entrapments can happen in various locations within the horse’s abdominal cavity, each described by a specific term: [1][2][3]

  • Mesenteric rent
  • Epiploic Foramen
  • Gastrosplenic Entrapment
  • Nephrosplenic Entrapment

Internal entrapments often result in severe pain and require prompt veterinary intervention as these conditions can become life-threatening.

Mesenteric Rent

In cases of mesenteric rent, part of the small intestine gets trapped in a tear or hole (known as a rent) in the mesentery. The mesentery is a fan-shaped organ that attaches the intestines to the abdominal wall. It loosely holds the gastrointestinal tract in place and supplies it with blood vessels and nerves. [1][3]

Epiploic Foramen

In this form of entrapment, part of the horse’s small intestine gets trapped in the epiploic foramen (also known as the omental foramen). The foramen is a natural opening of between 4 and 6 cm (1.5 – 3 in) in the omentum, which is a large fatty membrane that covers the abdominal organs. [4][5][6]

This membrane helps to protect the organs, stores fat, and plays a role in immune function. It also acts as a pathway for blood vessels and nerves. [4][5][6][7][8][9][10]

Gastrosplenic Entrapment

In these cases, part of the small intestine gets trapped in a hole in the gastrosplenic ligament. The gastrosplenic ligament is a band of tissue that attaches the stomach to the spleen. It helps maintain the positions of the stomach and the spleen within the horse’s abdominal cavity while also supplying blood to parts of these organs. [1][3][11]

Nephrosplenic Entrapment

This form of entrapment describes when part of the small intestine gets trapped either in the space between the spleen and the body wall, or in the nephrosplenic space. The nephrosplenic space is a small area formed by the side of the spleen and the side of the kidney. [12] The large colon can also become trapped in this space, often referred to as left dorsal displacement.

Symptoms

The main sign of internal entrapments is colic. [5][11] Colic is a broad term for abdominal pain in horses.

Signs of colic include: [13][14][15][16]

  • Lethargy
  • Watching the flank
  • Restlessness such as shifting weight, nibbling, circling, or staring off
  • Grinding teeth
  • Adopting unusual positions like stretching out, crouching, lying on the back, or dog sitting
  • Curling the upper lip (Flehmen response)
  • Pawing
  • Tensing the abdomen
  • Kicking the abdomen
  • Lying down
  • Rolling
  • Elevated heart rate

Additional symptoms of nephrosplenic entrapment in horses include: [12]

  • Tacky mucous membranes (dehydration)
  • Decreased intestinal noises

Risk Factors

The risk factors for each specific type of internal entrapment vary.

Mesenteric rent entrapments can occur in horses of any age or breed. It is more common in female horses, particularly in broodmares as a result of the movements of the foal before and during birth. [1][3]

Epiploic foramen entrapment is the most common form of intestinal entrapments in horses. [17] It can occur in horses of any age. [1][2][3]

Epiploic foramen entrapment was once thought to affect older horses more often, but this has since been disproven. [3] This condition is reported more often during the winter. [2][3]

Other risk factors include: [1][2][7][9][18]

Gastrosplenic entrapment is a rare condition. [11] It can occur in horses of any breed or age but is mostly reported in older horses. [1][11] Geldings are more susceptible than stallions or mares. [1]

Nephrosplenic entrapment of the small intestine is very rare. The risk factors for this condition are not yet well understood. [12]

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Causes

The causes of equine intestinal entrapments are not fully understood at this time. Similar to displacement colic, where the large intestine gets displaced within the abdominal cavity, the flexible and free-floating nature of the horse’s small intestine is likely a contributing factor. [1]

Mesenteric tears may be present at birth or arise from injuries to the mesentery. Injuries may be due to: [1][3]

  • Parasites
  • Gastric impaction
  • Mesodiverticular band (a band of tissue that attaches the mesentery to the intestine)
  • Teratomas (a tumor that contains hair, muscle, or other structures)

The causes of epiploic foramen entrapment are not yet well understood. Considerations include: [4]

  • Morphology of the foramen
  • Rhythmic motion of the diaphragm, liver, and abdominal wall
  • Differences in pressure within the abdomen during cribbing

Tears in the gastrosplenic ligament may be present at birth. In cases where they develop later, they have been associated with: [11]

  • Trauma
  • Increased abdominal pressure due to pregnancy
  • Dystocia
  • Severe gastrointestinal distention
  • Strenuous exercise
  • Congenital defects

The cause of nephrosplenic entrapment is unknown at this time. [12]

Severity

The severity of mesenteric rent entrapment varies based on the amount of intestine that has made its way into the hole and whether the blood flow to the intestine is restricted. [1][3]

In mesenteric rents, the size of the hole is also a factor – larger holes are correlated with less severe strangulation. [3] Smaller holes in the mesentery result in a tighter constriction around trapped intestine, increasing the likelihood if interrupting blood supply and subsequent tissue death. [3]

It is possible for more than one rent in the mesentery to occur at the same time, which means that more than one segment of the intestine can become trapped. [3] Mares that give birth more than once are at risk of reopening the same tears in the mesentery in subsequent pregnancies. [3]

Epiploic foramen entrapment is a life-threatening condition in horses. [7] The severity of this entrapment is also based on the amount of intestine that has made its way into the space. [1][5]

Other factors include: [19]

  • The direction of the epiploic entrapment
  • Whether the blood supply is cut off
  • Whether ingesta becomes impacted in the trapped segment
  • Which specific structures of the small intestine are involved

Usually, this condition involves the ileum (the last segment of the small intestine), but sometimes other segments of the small intestine are trapped as well. [1] In some cases, this condition is accompanied by intra-abdominal hemorrhage. [2][19]

In rare instances, the large colon can also become trapped in the foramen. [2] It is also possible for more than one loop of small intestine to become trapped at the same time. [3]

Epiploic foramen entrapment sometimes recurs even after surgical intervention. [1] In other cases, the foramen closes after the surgical procedure and the horse is no longer in danger of this condition. [1]

The severity of gastrosplenic entrapment depends on the amount of intestine involved, and the position of the intestine in the tear. [1][5] Typically, it is the ileum or the ileum and the jejunum that get trapped in the gastrosplenic ligament. [11] Gastrosplenic entrapment does not recur once surgically resolved. [1][11]

The severity of nephrosplenic entrapment depends on the amount of intestine involved, and whether the blood flow to the trapped portion is disrupted. Nephrosplenic entrapment occurs more often with the large intestine. [1]

Entrapment colic is always a medical emergency. Horses with signs of colic require prompt veterinary evaluation.

Diagnosis

It is usually necessary to perform exploratory surgery to investigate and confirm diagnosis of intestinal entrapments in horses. [1]

Of all of the forms of internal entrapments, the epiploic foramen entrapment may be easier to detect without exploratory surgery based on: [3][4]

  • Ultrasound
  • Abdominocentesis (sampling fluid from the abdominal cavity)

Additional diagnostic tools may include: [1][11][12]

  • Physical exam
  • Rectal palpation
  • Nasogastric intubation

Treatment

Treatment for all forms of entrapment colic in horses usually requires surgery. [1][2][3][18]

Exploratory surgery for entrapments is performed under general anesthesia. Depending on the nature of the entrapment, the surgeon may be able to manually replace the structures without further surgical invasion. [3]

In severe cases, a section of the intestine may need to be completely excised. If tissue death has occurred, the dead tissue needs to be removed and the tract must be surgically repaired. [3]

The recovery from colic surgery is complex, and intensive care is usually required for these conditions. [17] Hospitalization and stall rest may last for several weeks or more.

Prognosis

The prognosis for horses with mesenteric rent entrapment is guarded. If the horse survives surgery, the prognosis improves greatly. [1] Mares that undergo surgery to repair a mesenteric rent entrapment have a high success rate in foaling the following spring. [3]

The prognosis for horses with epiploic foramen entrapment is fair with early detection. [1][4][6][20] If the horse survives surgery, the prognosis is good. [1]

The prognosis for horses with gastrosplenic entrapment with surgical intervention is fairly good. The prognosis for horses with nephrosplenic entrapment is not known at this time, as cases are rare. [1][11]

Prevention

There are no specific preventive measures for equine intestinal entrapments. Currently, surgical techniques are in development to close the foramen as a preventive against epiploic foramen entrapment. [4][6]

It has been reported that closing the nephrosplenic space during surgery in the first instance of nephrosplenic entrapment can reduce recurrence of this condition. [21]

Given the lack of prevention available for these conditions, the most effective strategies are management strategies that optimize the horse’s digestive health and minimize stress and anxiety.

Feeding a balanced, forage-based diet and providing free access to salt and clean, fresh water are important for digestive health horses.

You can ensure your horse is receiving a balanced diet by consulting with a qualified equine nutritionist. Book a free consultation online to discuss your horse’s needs with our expert nutritionists and veterinarians.

Summary

Internal entrapments are a group of conditions where a segment of the horse’s small intestine becomes trapped in other structures within the abdomen.

  • Specific entrapments include mesenteric rent entrapment, epiploic foramen entrapment, gastrosplenic entrapment, and nephrosplenic entrapment.
  • The main symptom of all equine internal entrapments is colic.
  • Causes are mostly unknown. Diagnosis and treatment usually require surgery.
  • Prognosis varies depending on the severity of the condition and whether surgery is successful.

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References

  1. Blikslager, A. T., et al., Eds. The Equine Acute Abdomen. Third edition. Wiley, Blackwell, Hoboken, NJ. 2017.
  2. Reed, S. M., et al. Equine Internal Medicine. 3rd ed. Saunders Elsevier, St. Louis, Mo. 2010.
  3. Auer, J. A. Equine Surgery. 5th edition. Elsevier, St. Louis, MO. 2018.
  4. Van Bergen, T., et al. Equine Colic Associated with Small Intestinal Epiploic Foramen Entrapment. The Veterinary Journal. 2021. View Summary
  5. Kilcoyne, I., et al. Comparison of Clinical Findings and Short-Term Survival between Horses with Intestinal Entrapment in the Gastrosplenic Ligament and Horses with Intestinal Entrapment in the Epiploic Foramen. Journal of the American Veterinary Medical Association. 2016. View Summary
  6. Grulke, S., et al. Mesh Closure of Epiploic Foramen by Ventral Laparotomy in 17 Horses with Entrapment. Veterinary Record. 2020. View Summary
  7. Van Bergen, T., et al. Surgical Treatment of Epiploic Foramen Entrapment in 142 Horses (2008–2016). Veterinary Surgery. 2019. View Summary
  8. Freeman, D. E. Surgery of the Small Intestine. Veterinary Clinics of North America: Equine Practice. 1997. View Summary
  9. Archer, D. C., et al. Risk Factors for Epiploic Foramen Entrapment Colic: An International Study. Equine Veterinary Journal. 2008. View Summary
  10. Archer, D. C., et al. Entrapment of the Small Intestine in the Epiploic Foramen in Horses: A Retrospective Analysis of 71 Cases Recorded between 1991 and 2001. The Veterinary Record. 2004.
  11. Ortved, K. F. Clinical Considerations of Intestinal Entrapment through the Gastrosplenic Ligament in the Horse. Equine Veterinary Education. 2013.
  12. Goodrich, L. R., et al. Entrapment of the Small Intestine within the Nephrosplenic Space in Two Horses. Equine Veterinary Education. 1997.
  13. Dukti, S., & White, N. A. Prognosticating Equine Colic. The Veterinary Clinics of North America: Equine Practice. 2009.
  14. Cook, V. L., & Hassel, D. M. Evaluation of the Colic in Horses: Decision for Referral. The Veterinary Clinics of North America: Equine Practice. 2014.
  15. Gillen, A., & Archer, D. C. Epidemiology of Colic: Current Knowledge and Future Directions. Veterinary Clinics of North America: Equine Practice. 2023.
  16. Torcivia, C., & McDonnell, S. Equine Discomfort Ethogram. Animals. Multidisciplinary Digital Publishing Institute. 2021.
  17. Bergren, A. L., et al. Retrospective Comparison of Gastrosplenic Entrapment of the Small Intestine to Other Strangulating Small Intestinal Lesions in Adult Horses. Veterinary Surgery. 2015. View Summary
  18. Archer, D. C., et al. Factors Associated with Survival of Epiploic Foramen Entrapment Colic: A Multicentre, International Study. Equine Veterinary Journal. 2011. View Summary
  19. Wanstrath, M. A., et al. Surgical Enlargement of the Epiploic Foramen in Horses. Veterinary Surgery. 2023. View Summary
  20. Freeman, D. E., & Schaeffer, D. J. Short-Term Survival after Surgery for Epiploic Foramen Entrapment Compared with Other Strangulating Diseases of the Small Intestine in Horses. Equine Veterinary Journal. 2010.
  21. Arévalo Rodríguez, J. M., et al. Nephrosplenic Space Closure Significantly Decreases Recurrent Colic in Horses: A Retrospective Analysis. Veterinary Record. 2019.