Colic is the number one cause of death in horses and one of the highest-yield equine topics on the NAVLE. The exam tests your ability to classify colic type, interpret diagnostic findings, choose appropriate analgesia, and—most critically—know when a horse needs to go to surgery. Get those surgical indicators down cold.
Classification: Medical vs Surgical Colic
Medical Colic
- Spasmodic colic — hyperperistalsis; responds to antispasmodics
- Impaction — pelvic flexure most common site; also cecal, right dorsal
- Sand colic — ventral “ocean waves” sound on auscultation
- Large colon displacement (many are medical)
- Gastric dilation (secondary to SI obstruction)
Generally: responds to analgesics, HR <60, no reflux, clear peritoneal fluid
Surgical Colic
- Small intestinal volvulus — most rapidly fatal
- Large colon volvulus (270–360°)
- Strangulating lipoma — older horses; SI strangulation
- Intussusception — small intestine
- Epiploic foramen entrapment — right side; cannot reduce medically
- Nephrosplenic entrapment (if medical fails)
Generally: unrelenting pain, HR >60, reflux >2L, abnormal peritoneal fluid
Initial Evaluation
Vital Signs
Heart rate is the single most important clinical parameter in colic triage:
- HR <48 bpm — mild pain; likely medical
- HR 48–60 bpm — moderate pain; careful monitoring
- HR >60 bpm — significant pain or cardiovascular compromise; serious
- HR >80 bpm — severe; surgical emergency until proven otherwise
Mucous membranes and CRT: pale/pink = adequate perfusion; pale/gray/tacky + CRT >2 seconds = cardiovascular compromise = surgical indicator.
Nasogastric Intubation
Passing a nasogastric (NG) tube is mandatory in every colic evaluation. Horses cannot vomit—if fluid accumulates in the stomach from an obstructed small intestine, the stomach can rupture. Gastric reflux >2 liters is considered significant and indicates small intestinal obstruction proximal to the reflux point. Volumes >10L are not uncommon in severe SI strangulation.
Rectal Palpation
Findings that indicate surgical conditions:
- Taut nephrosplenic (renosplenic) ligament + medially displaced spleen = nephrosplenic entrapment
- Distended, tense small intestinal loops = SI obstruction
- Gas-distended cecum with tension on cecal band = cecal impaction or volvulus
- Palpable lipoma stalk = strangulating lipoma
Abdominocentesis (Peritoneal Fluid)
Serosanguineous peritoneal fluid = strangulating obstruction with intestinal necrosis. This is a surgical emergency. If you inadvertently puncture a loop of intestine (enterocentesis), the fluid will have obvious feed material and bacteria on cytology.
Analgesia
Specific High-Yield Conditions
Nephrosplenic (Left Dorsal) Entrapment
The left large colon becomes trapped in the nephrosplenic space between the left kidney and spleen. Classic rectal finding: spleen displaced medially (you can feel its medial border), absent gas shadow between left kidney and spleen (the space is filled by colon).
Medical treatment: phenylephrine 0.02 mg/kg IV (splenic contraction) + rolling under general anesthesia. Success rate ~50–60%. Jogging/trotting may help dislodge the colon before anesthesia. If medical management fails: surgical correction.
Large Colon Volvulus
Volvulus of the large colon (typically at the cecocolic attachment) with 270–360° rotation. This is one of the most rapidly fatal forms of colic—devascularization of the large colon leads to necrosis within hours. Presentation: acute severe abdominal pain, massive tympanic distension, cardiovascular shock. The horse deteriorates rapidly despite analgesics. Mortality is 50–70% even with emergency surgery.
Strangulating Lipoma
Pedunculated lipomas—benign fat tumors on mesenteric stalks—are a common cause of small intestinal strangulation in older horses (>15 years). The lipoma wraps around a loop of SI, cutting off blood supply. Presentation: moderate-to-severe colic in an older horse, nasogastric reflux, small intestinal distension on rectal palpation. Diagnosis is confirmed at surgery. Resection of devitalized intestine is required.
Cecal Impaction
Cecal impaction is treacherous—horses show minimal pain despite significant cecal compromise. The cecum has a functional blind end and cannot empty effectively without motility. By the time pain becomes obvious, the cecum may be severely distended or compromised. Diagnosis: rectal palpation of a firm cecal body in the right dorsal abdomen. Treatment: aggressive IV fluid therapy (6–12 L/hr), laxatives (DSS); surgical cecal bypass (typhlotomy) if no response within 24–48 hours.
Surgical Decision Criteria
The NAVLE loves this topic. Know these indicators: