Right Dorsal Displacement in Horses: Understanding the Causes Behind a Common Surgical Colic

The equine large colon is one of the most mobile structures within the gastrointestinal tract. Because it has relatively few attachments to the body's wall, it can shift into abnormal positions within the abdomen, resulting in various forms of displacement¹. Among the recognized non-strangulating large colon displacements, right dorsal displacement (RDD) remains a significant cause of surgical colic in horses.

The Mobile Nature of the Equine Large Colon

Four primary forms of non-strangulating large colon displacement have been described: left dorsal displacement, right dorsal displacement, retroflexion of the pelvic flexure, and non-strangulating volvulus. These conditions result in partial or complete obstruction of intestinal contents without compromising blood supply to the affected bowel segment¹.

RDD occurs when the pelvic flexure moves backward, and the left colon migrates cranially and toward the right side of the abdomen. As the displacement progresses, portions of the large colon become positioned between the cecum and the right abdominal wall¹.

Why Does Right Dorsal Displacement Occur?

The exact cause of RDD remains incompletely understood. Current theories suggest that abnormal gastrointestinal motility plays a central role in its development. Changes in pacemaker activity within the pelvic flexure may promote abnormal shortening of the colon and movement of the pelvic flexure toward the diaphragm, facilitating displacement¹.

Dietary factors have also been implicated. Excessive intake of soluble carbohydrates can increase fermentation within the large colon, resulting in gas accumulation, colonic distension, and migration of the bowel. In addition, alterations in the fecal microbiota may affect colonic motility and predispose horses to displacement^1,2.

As with many cases of equine colic, however, the underlying cause often remains unknown, suggesting that multiple mechanisms may contribute to disease development.

More Than a Mechanical Problem

Many horses diagnosed with RDD have concurrent findings during surgery, including impactions, colonic congestion, and edema^3,4. These associated lesions indicate that RDD may represent a broader disturbance in gastrointestinal function rather than simply an isolated displacement.

Chronic inflammation and reduced oxygen delivery to intestinal tissues may alter large colon motility, increasing the risk of displacement. Such changes may help explain why many affected horses experience prolonged periods of mild colic before referral¹.

The Importance of Early Recognition

Unlike acute strangulating lesions, horses with RDD frequently present with low-grade colic signs that may persist for several days before surgical intervention is pursued¹. This delay can allow inflammation and motility disturbances to worsen, potentially affecting postoperative recovery.

Key Takeaway for Practitioners

RDD remains a complex disorder with an incompletely understood pathogenesis. While altered motility, dietary factors, microbial changes, and inflammation have all been implicated, further research is needed to clarify the mechanisms involved. Improved understanding of these processes may ultimately help veterinarians develop more effective prevention and management strategies for this challenging condition.

References  

1. Whyard JM, Brounts SH. Complications and survival in horses with surgically confirmed right dorsal displacement of the large colon. The Canadian Veterinary Journal. 2019 Apr;60(4):381. https://pmc.ncbi.nlm.nih.gov/articles/PMC6417614/pdf/cvj_04_381.pdf  

2. Weese JS, Holcombe SJ, Embertson RM, Kurtz KA, Roessner HA, Jalali M, Wismer SE. Changes in the faecal microbiota of mares precede the development of post partum colic. Equine veterinary journal. 2015 Nov;47(6):641-9. https://doi.org/10.1111/evj.12361  

3. McGovern KF, Suthers JM, James FM, O'Meara BJ, Parker RA, Foote AK, Bladon BM. Gastric impaction associated with displacement and volvulus of the large colon in seven mature horses. Equine Veterinary Education. 2015 Sep;27(9):453-9. https://doi.org/10.1111/eve.12396  

4. Blikslager AT. Gastric impaction and large colon volvulus: Can one lead to the other?. Equine Veterinary Education. 2015 Sep;27(9):460-1. https://doi.org/10.1111/eve.12417