Colic is the leading cause of emergency death in horses, and it shows up constantly on the NAVLE. Not because it's rare — it accounts for 10–15% of all equine visits — but because the decisions are genuinely hard and the stakes are high. The exam tests your ability to triage fast: who gets fluids and a walk, and who needs a trailer to surgery right now.
The anatomy is the whole story. The equine large colon is 3–4 meters long, holds up to 76 liters, and has almost no mesenteric attachments to the body wall. It just floats. That freedom is why it displaces, twists, and becomes trapped in ways no other species can manage.
Medical vs. Surgical Colic: The Decision That Defines the Case
The first question in every colic case is not "what type of colic is this?" — it's "does this horse need surgery?" Most colics are medical. But missing a surgical case costs a horse its life. These indicators push you toward the OR:
| Parameter | Medical Colic | Surgical Colic |
|---|---|---|
| Heart rate | < 60 bpm | ≥ 60 bpm |
| Pain response | Responds to analgesics | Unresponsive or recurrent |
| Nasogastric reflux | Absent (< 2 L net) | ≥ 2 L net reflux |
| Peritoneal fluid | Clear, straw-colored; TP < 2.5 g/dL | Serosanguinous; TP > 2.5 g/dL |
| Colon wall (ultrasound) | < 9 mm | ≥ 9 mm → call the surgeon |
| PCV | < 50% | > 50% |
| Small intestine (rectal) | Not palpable | Distended loops palpable |
| Gut sounds | Present (may be hypermotile) | Absent |
Colic Types You Need to Know Cold
| Type | Mechanism | Pain Level | Rectal Finding | NG Reflux | Treatment |
|---|---|---|---|---|---|
| Spasmodic | Intestinal hypermotility, gas accumulation | Mild–moderate, intermittent | Normal or gas-filled colon | None | Buscopan (hyoscine-butylscopolamine) ± flunixin; usually resolves in 30–60 min |
| Large Colon Impaction | Dehydrated ingesta; pelvic flexure most common site | Mild–moderate, intermittent | Firm doughy mass at pelvic flexure | None | IV fluids, mineral oil or MgSO4 via NG tube, analgesia; surgery if refractory |
| Left Dorsal Displacement (NSE) | Left colon traps over nephrosplenic ligament | Mild–moderate, left-sided | Left kidney cannot be reached; colon displaced medially | None | Phenylephrine + exercise (rolling); or surgery if medical fails |
| Right Dorsal Displacement (RDC) | Large colon displaced between cecum and body wall | Moderate, right-sided | Colonic bands run craniodorsal to caudoventral (right side); cecum pushed left | None typically | Surgery (right flank or ventral midline) |
| Large Colon Volvulus (LCV) | Rotation ≥ 270°; strangulating; complete blood supply occlusion | Severe, violent, unrelenting | Massively distended colon; tympanic; no normal landmarks | None (large colon, not SI) | Emergency surgery only |
| SI Obstruction / Strangulation | Pedunculated lipoma, volvulus, intussusception | Severe, rapid onset | Distended small intestinal loops (≥ 5 cm diameter) | ≥ 2 L net reflux | Emergency surgery |
Medical vs. Surgical Decision Flow
- HR < 60 bpm
- Pain responds to analgesia
- No NG reflux
- No distended SI loops
- Normal peritoneal fluid
- Colon wall < 9 mm
- HR ≥ 60 bpm
- Refractory pain
- NG reflux ≥ 2 L
- Distended SI on rectal
- Serosanguinous fluid
- Colon wall ≥ 9 mm
- PCV > 50%
Nasogastric Tube: Why You Never Skip It
Every colic horse gets an NG tube passed. This is not optional. The horse cannot vomit, so if the stomach is accumulating fluid from a proximal obstruction, you have to decompress it — otherwise gastric rupture kills the horse before surgery does.
Net reflux ≥ 2 liters is the threshold that matters. That volume means the stomach is filling faster than it empties. The source is almost always a small intestinal obstruction: duodenitis-proximal jejunitis (DPJ), SI volvulus, ileal impaction, or strangulation via a pedunculated lipoma. Once you see that volume of reflux, you're looking at a surgical case until proven otherwise — and DPJ is the one exception where surgery won't help.
Rectal Palpation: What You're Feeling For
You can only reach 25–30% of the abdominal cavity, but that 30% tells you a lot. Normal palpable structures: pelvic flexure, cecal base, and the aorta. Small intestine should not be palpable. If you feel it, and it's distended, that's already a surgical problem.
The findings that change management:
Pelvic flexure impaction: Firm, doughy mass at the pelvic inlet. It doesn't move when you push it. You can feel the pelvic flexure is loaded. No other loops distended.
Large colon volvulus: Massive, tympanic, gas-distended colon that fills your entire reach. Normal anatomical landmarks — the bands and haustra — are obliterated. You can't identify specific structures. The whole dorsal abdomen is tightly packed with gas. Heart rate is already ≥ 60 bpm before you even get to the rectum.
Nephrosplenic entrapment (NSE/LDC): The left kidney is NOT palpable. Normally you can feel it dorsolaterally. In NSE, the colon is sitting between you and the kidney, blocking access. Colon bands are running craniodorsally instead of the normal orientation.
Right dorsal displacement (RDC): Colonic bands running craniodorsal to caudoventral on the right side. The cecum may be displaced medially. This is a surgical displacement in most cases.
Distended SI loops: Smooth, sausage-shaped structures, ≥ 5 cm diameter, arranged like loops of garden hose. Each one you feel adds urgency. Combined with NG reflux, this is the most reliable surgical indicator from rectal exam alone.
Large Colon Volvulus: The One You Cannot Miss
LCV is the highest-stakes colic diagnosis. Rotation ≥ 270 degrees causes complete occlusion of the blood supply. Ischemia starts immediately. The colon goes from viable to necrotic in hours. Short-term survival is 35–86%, and that wide range reflects exactly how quickly the case deteriorates if you delay.
The classic presentation: postpartum mare, acute onset, severe unrelenting pain that does not respond to xylazine or flunixin, HR ≥ 80 bpm, brick-red or purple mucous membranes with a toxic line, CRT ≥ 3 seconds, absent gut sounds, progressive abdominal distension, colon wall ≥ 9 mm on FLASH ultrasound. That's a horse that needs to be in a trailer in under an hour.
Why postpartum mares? Because foaling creates sudden increased abdominal space. The large colon has room to rotate that it didn't have before. This is a well-established risk factor. The NAVLE uses it reliably.
Nephrosplenic Entrapment: The Medical Option
NSE is a nonstrangulating displacement — blood supply is intact. That's why prognosis is excellent (> 90% survival) and medical management is a legitimate first-line option. The left colon migrates dorsally and gets trapped over the nephrosplenic ligament between the spleen and left kidney. Deep-chested, large-bodied horses (Warmbloods) are overrepresented.
Medical management: phenylephrine (0.02–0.05 mg/kg IV or IM) contracts the spleen, shrinking the space the colon is trapped in, then vigorous exercise or rolling dislodges the colon. Success rate with phenylephrine + exercise is around 80%. If that fails, right flank laparotomy under standing sedation is an option. Surgery has equivalent survival to medical management — pick based on response to treatment.
Large Colon Impaction: The Common One
Pelvic flexure impaction is the most common surgical-referral-level colic that actually gets treated medically. The pelvic flexure narrows from 25 cm to 8–10 cm diameter with a 180-degree turn — impaction almost always starts there. Dehydration, coarse forage, stall confinement, and dental disease are the usual contributors.
Clinical picture: mild to moderate intermittent pain, decreased fecal output, dry fecal balls, HR 40–60 bpm, gut sounds decreased, no NG reflux. Rectal exam finds a firm doughy mass extending from the pelvic flexure into the left caudal abdomen. Treatment: aggressive IV fluid therapy (3–5 L/hr initially), mineral oil or MgSO4 via NG tube, analgesia with flunixin (1.1 mg/kg IV). Prognosis > 95% with early treatment.
Cecal impaction carries worse prognosis (60–80%) because cecal rupture is the risk if impaction is forced — treat more conservatively, surgery earlier if no improvement.
Peritoneal Fluid Interpretation
Normal peritoneal fluid: straw-colored, clear enough to read through, TP < 2.5 g/dL, nucleated cell count < 5,000 cells/μL. When the bowel is ischemic, the fluid changes. Serosanguinous (blood-tinged, pink to red) fluid means intestinal strangulation until proven otherwise. TP > 2.5 g/dL alone can be significant. Peritoneal lactate > 2 mmol/L is a specific marker for intestinal strangulation — this number shows up on NAVLE questions.