NAVLE Gastrointestinal and Digestive

Equine Colic Study Guide

March 28, 2026 25 min read 4 views
Colic is the leading cause of emergency presentation and death in horses, accounting for approximately 10-15% of all equine veterinary visits.

Overview and Clinical Importance

Colic is the leading cause of emergency presentation and death in horses, accounting for approximately 10-15% of all equine veterinary visits. The term encompasses any condition causing abdominal pain, though gastrointestinal disorders are the most common etiology. Understanding the classification, diagnosis, and management of colic is essential for NAVLE success.

The equine large colon presents unique anatomical challenges: it is 3-4 meters long, holds up to 76 liters, and critically, has minimal mesenteric attachments to the body wall. This mobility predisposes horses to displacements and volvulus. The large colon consists of the right ventral colon, sternal flexure, left ventral colon, pelvic flexure, left dorsal colon, diaphragmatic flexure, right dorsal colon, and transverse colon.

Classification Examples Key Features
Nonstrangulating Obstruction Impaction, enteroliths, sand colic Lumen blocked, blood supply intact; mild-moderate pain; often medical treatment
Strangulating Obstruction Large colon volvulus greater than 270 degrees, small intestinal strangulation Blood supply compromised; severe pain; immediate surgery required
Displacement Nephrosplenic entrapment (LDD), right dorsal displacement Colon moves out of normal position; variable treatment
Inflammatory/Functional Enteritis, colitis, peritonitis, spasmodic colic Inflammation or motility dysfunction; diarrhea or fever possible

Classification of Equine Colic

Equine colic can be classified by mechanism, location, and whether medical or surgical intervention is required.

High-YieldOn NAVLE, distinguish strangulating from nonstrangulating lesions. Strangulating lesions cause severe, unrelenting pain, rapid cardiovascular deterioration (HR greater than 60 bpm), and serosanguinous peritoneal fluid. These require IMMEDIATE surgery.
Parameter Normal Clinical Significance
Heart Rate 28-44 bpm HR greater than 60 = severe pain/compromise; greater than 80 suggests strangulation
Temperature 99-101.5 F Fever = enteritis/colitis; hypothermia = shock; take BEFORE rectal
CRT Less than 2 sec Greater than 3 sec = dehydration/cardiovascular compromise
Mucous Membranes Pink, moist Pale = shock; brick red = endotoxemia; toxic line present in sepsis
Gut Sounds Present all quadrants Absent = ileus/obstruction; hypermotile = spasmodic colic

Diagnostic Approach to Colic

Physical Examination Parameters

Rectal Examination

Rectal palpation is essential in colic evaluation, though only 25-30% of the abdominal cavity is accessible. Key structures: pelvic flexure, cecal base, small intestine (should NOT be palpable normally), aorta, nephrosplenic ligament.

NAVLE TipRectal tears are the most common cause of equine veterinary malpractice litigation. Always use adequate lubrication, proper restraint, and gentle technique. Grade 4 tears (peritoneal perforation) are frequently fatal.

Abdominocentesis and Peritoneal Fluid

Normal peritoneal fluid is straw-colored and clear enough to read newspaper print through it.

Abdominal Ultrasonography (FLASH Technique)

The Fast Localized Abdominal Sonography of Horses (FLASH) protocol allows rapid field assessment of colic patients.

Rectal Finding Interpretation
Firm, doughy pelvic flexure Pelvic flexure or left ventral colon impaction
Taenia coursing dorsally toward left kidney Nephrosplenic entrapment (left dorsal displacement)
Distended, turgid small intestine Small intestinal obstruction/strangulation - SURGICAL EMERGENCY
Edematous, thickened bowel wall Vascular compromise - indicates need for surgery

Pelvic Flexure and Large Colon Impaction

Pathophysiology

Large colon impactions are nonstrangulating obstructions caused by dehydrated, compacted ingesta. The pelvic flexure is the most common site due to its dramatic decrease in luminal diameter (25 cm to 8-10 cm) and 180-degree turn.

Risk Factors

  • Dehydration or inadequate water intake (especially cold weather)
  • Sudden dietary changes or poor-quality, coarse forage
  • Stall confinement or decreased exercise
  • Dental disease leading to inadequate mastication
  • Older horses and debilitated animals

Clinical Signs

  • Mild to moderate, intermittent abdominal pain
  • Decreased fecal output; dry, hard fecal balls
  • Mildly elevated heart rate (40-60 bpm)
  • No nasogastric reflux
  • Rectal: firm, doughy mass extending cranially from pelvic flexure

Treatment

High-YieldPrognosis for simple pelvic flexure impaction is EXCELLENT with greater than 95% survival. Key is early recognition and aggressive fluid therapy. Cecal impactions carry worse prognosis (60-80% survival).
Parameter Normal Abnormal Findings
Color Straw/pale yellow Orange = early strangulation; serosanguinous = advanced; green = rupture
Total Protein Less than 2.5 g/dL Increases FIRST (1-2 hrs) in strangulation before WBC rises
Nucleated Cells Less than 5,000-10,000/uL Elevated with peritonitis, strangulation (3-6 hrs after onset)
Lactate Less than 2.0 mmol/L Elevated = intestinal ischemia; peritoneal lactate rises BEFORE plasma

Large Colon Volvulus

Pathophysiology

Large colon volvulus (LCV) is rotation of the large colon on its mesenteric axis, typically at the cecocolic ligament. Volvulus greater than or equal to 270 degrees causes strangulating obstruction with complete occlusion of blood supply, leading to rapid ischemia, necrosis, and endotoxemia.

LCV accounts for 10-20% of surgical colic cases. Short-term survival: 35-86%. This is one of the most devastating forms of colic.

Risk Factors

  • Postpartum mares: highest risk group; increased abdominal space after foaling
  • Minimal mesenteric attachments of left ventral and dorsal colon
  • Previous large colon displacement (15% recurrence rate)
  • High-fermentable diets producing excess gas

Clinical Signs

LCV presents with severe, unrelenting, violent colic that is refractory to standard analgesics.

  • Acute onset of severe, uncontrollable pain (rolling, thrashing)
  • Rapid cardiovascular deterioration: HR greater than 60-80 bpm
  • Prolonged CRT, toxic mucous membranes
  • Progressive abdominal distension
  • Absent gut sounds
NAVLE TipPostpartum mare + acute severe colic + abdominal distension = LARGE COLON VOLVULUS until proven otherwise. This is a surgical emergency. Do NOT delay referral.

Treatment

IMMEDIATE SURGICAL INTERVENTION is required. There is no medical treatment for strangulating LCV. Prognosis worsens with each hour of delay.

  • Ventral midline celiotomy under general anesthesia
  • Extensive needle decompression of gas-distended colon
  • Manual correction (derotation) of volvulus
  • Assessment of colon viability
  • Large colon resection if non-viable
High-YieldReported short-term survival for LCV is 35-86%; long-term around 30-48%. Best outcomes with short duration of illness and rapid surgical intervention. PCV greater than 50%, HR greater than 80, black mucosal color = poor prognosis.
Finding Significance
Large colon wall greater than 9 mm Highly suggestive of large colon volvulus - SURGICAL
Small intestine greater than 3 cm diameter SI obstruction; amotile distended loops = strangulation
Left kidney NOT visible Nephrosplenic entrapment (gas-filled colon obscures kidney)

Nephrosplenic Entrapment (Left Dorsal Displacement)

Pathophysiology

Nephrosplenic entrapment (NSE), also called left dorsal displacement of the large colon (LDDLC), occurs when the left colon migrates dorsally and becomes trapped over the nephrosplenic ligament between the spleen and left kidney.

This is a nonstrangulating obstruction - blood supply is typically NOT compromised. NSE accounts for 6-9% of horses presented for colic and has an EXCELLENT prognosis.

Risk Factors

  • Large body size, deep-chested conformation (Warmbloods)
  • Deep nephrosplenic space (anatomical predisposition)
  • Middle-aged to older horses

Diagnosis

NAVLE TipOn NAVLE, if 'left kidney cannot be visualized on ultrasound' in a horse with mild left-sided colic = NEPHROSPLENIC ENTRAPMENT.

Treatment

High-YieldNSE has EXCELLENT prognosis with greater than 90% survival. Recurrence rate 3-23%. Meta-analyses show no significant difference in survival between medical and surgical treatment.
Treatment Protocol Mechanism
IV Fluids LRS; 2-4 L/hour initially Rehydrates ingesta; MOST IMPORTANT treatment
Enteral Fluids 4-8 L water via NG tube q2-4h Safe, effective; can supplement/replace IV
Mineral Oil 2-4 L via NG tube daily Lubricant; passage indicates GI transit
DSS 10-20 mg/kg single dose Surfactant/stool softener; do NOT repeat 48h
Analgesics Flunixin 1.1 mg/kg IV q12h Pain control; response is prognostic

Memory Aids and Board Tips

"COLIC PAIN" - Indicators for Surgery

C - Cardiovascular deterioration (HR greater than 60)

O - Obstruction with distended small intestine

L - Lactate elevated (peritoneal greater than 2 mmol/L)

I - Intractable pain not responsive to analgesics

C - Colon wall thickness greater than 9 mm on ultrasound

P - Peritoneal fluid serosanguinous

A - Absence of gut sounds

I - Increasing PCV (greater than 50%)

N - Nasogastric reflux with SI distension

Quick Memory Tips

"LEFT = LDD = NSE" - Left kidney not visible = Left Dorsal Displacement = Nephrosplenic Entrapment

"MARE FOALED = CHECK FOR VOLVULUS" - Postpartum mare with severe colic = Large colon volvulus #1 differential

"9 mm = 9-1-1" - Large colon wall greater than or equal to 9 mm = EMERGENCY surgical referral

Method Findings
Rectal Palpation Gas-distended left colon coursing dorsally; taeniae palpable over ligament; spleen shifted medially
Ultrasound LEFT KIDNEY NOT VISIBLE (obscured by gas in entrapped colon)
Abdominocentesis Typically NORMAL (blood supply not compromised)
Method Protocol Success Rate
Phenylephrine + Exercise 3 ug/kg/min IV x15 min, then 15-20 min lunging 63%; phenylephrine causes splenic contraction
Rolling Under Anesthesia GA, right lateral, rock side to side 84%; must be at surgical facility
Surgical Correction Ventral midline celiotomy When medical fails; EXCELLENT prognosis
NS Space Closure Laparoscopic obliteration Elective for recurrent NSE; 90% satisfaction
Condition Key Features Treatment Prognosis
Pelvic Flexure Impaction Mild pain; firm mass on rectal; no reflux IV/enteral fluids, mineral oil, DSS EXCELLENT (greater than 95%)
Large Colon Volvulus Severe pain; postpartum; HR greater than 60; wall greater than 9mm IMMEDIATE SURGERY GUARDED (35-86%)
Nephrosplenic Entrapment Mild pain; left kidney not visible on US Phenylephrine + exercise; rolling; surgery EXCELLENT (greater than 90%)

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