Equine Medicine

Clinical Reference Values (Adult)

Colic Assessment and Classification

Colic is a symptom complex, not a diagnosis. Initial triage determines medical vs. surgical need using the 5-Point Colic Scale (pain score, HR, CRT, mucous membranes, gut sounds).

Pain Grade:

• Grade 1-2 (Mild): Alert, normal behavior, occasional flank watching. Medical management likely.
• Grade 3 (Moderate): Restless, sweating, frequent lying down. Requires analgesia + diagnostics.
• Grade 4-5 (Severe): Violent thrashing, cardiovascular instability, shock. Surgical emergency.

Classification by Location:

• Foregut: Stomach, small intestine. Often medical (impaction, spasm, gastric dilation); some require surgery (strangulation, volvulus).
• Cecal: Impaction, rupture, overload. Often medical with aggressive fluid therapy; rupture is fatal.
• Large colon: Impaction, displacement, volvulus. Mixed medical/surgical.
• Small colon: Impaction, obstruction. Usually medical; surgery reserved for persistent cases.

Red flags for surgery: Severe pain unresponsive to analgesics, recurrent pain, prolonged nasogastric reflux (>2 liters), cardiovascular instability, peritoneal fluid with elevated protein/cell count.

Laminitis: Grading and Management

Obel Grading System (acute laminitis):

• Grade 1: Mild lameness; mild bounding digital pulses; distal limb heat. Weight-bearing normal.
• Grade 2: Obvious lameness; moderate bounding pulses; reluctance to bear weight on forelimbs. May sip water.
• Grade 3: Severe lameness; strong pulses; pronounced pain at digital vein pressure. May lie down; may not support weight.
• Grade 4: Severe lameness; horse may be unable to stand.

Acute Phase Management:

• Analgesia: NSAIDs (phenylbutazone 2-4 mg/kg BID or flunixin 1.1 mg/kg BID-TID). Consider opioids (butorphanol) for refractory pain.
• Support: Therapeutic farrier work (bar shoes, rockers), ice/cold therapy in early stage.
• Imaging: Radiographs to assess coffin bone rotation/penetration of distal phalanx. Digital thermography assesses laminar perfusion.
• Cause identification: Septic metritis, feed overload, trauma, PPID, metabolic syndrome.

Chronic Phase: Corrective shoeing, weight management, ongoing analgesia. Prognosis depends on radiographic findings and digital penetration.

Lameness Evaluation: Flexion Tests and Nerve Blocks

Systematic approach:

1. Observe: At walk and trot, straight and in circles. Determine forelimb vs. hindlimb; left vs. right.
2. Palpation: Hoof testers (digital pressure pain), joint effusion, digital pulses, heat, swelling.
3. Flexion tests: Flex joint 30-60 seconds; immediately trot out. Positive = increased lameness for 5-10 steps. Indicates pain in flexed structures (joints, tendons, ligaments, sole).
4. Nerve blocks: Desensitize regions progressively (palmar/plantar nerves, abaxial sesamoidean, low 4-point, high 4-point, etc.) until lameness resolves. Identifies anatomic pain location.
5. Imaging: Radiographs, ultrasound, nuclear scintigraphy, MRI as indicated.

NSAIDs in Equine Medicine

First-line analgesics: Phenylbutazone (4-6 mg/kg BID) and flunixin meglumine (1.1 mg/kg BID-TID).

Limitations:

• GI toxicity: NSAIDs increase colitis risk; prolonged use (>10 days) increases right dorsal colon ulceration risk.
• Renal concerns: Reduce if dehydrated; avoid in renal disease.
• Drug interactions: NSAIDs reduce cardiovascular output in shock; use cautiously in decompensated horses.
• Alternative: Firocoxib (a COX-2 selective inhibitor) may reduce GI side effects but is expensive.

Cushing's Disease (PPID) and Metabolic Syndrome

PPID (Pituitary Pars Intermedia Dysfunction): Age-related pituitary adenoma causing excessive ACTH.

• Clinical signs: Long, curly coat (often fails to shed); laminitis; polyuria/polydipsia; weight loss despite good appetite; immunosuppression.
• Diagnosis: Elevated ACTH (>35 pg/mL baseline; seasonal variation). ACTH stimulation test (dexamethasone, ACTH injection) if borderline.
• Management: Pergolide (dopamine agonist) to suppress ACTH. Reduce if laminitis develops.

Equine Metabolic Syndrome (EMS): Insulin resistance, obesity, laminitis risk.

• Diagnosis: Fasting glucose >110 mg/dL OR fasting insulin >20 μIU/mL (NEFA testing also useful).
• Management: Weight loss, low-NSC diet (<10% nonstructural carbohydrates), exercise, avoid pasture laminitis risk periods.

Pre-Purchase Examination Framework

Mandatory components:

1. Signalment & history: Age, breed, use, medical history, lameness history, prior surgeries.
2. Physical examination: Vital signs, body condition score, muscle symmetry, conformation, gait assessment.
3. Lameness evaluation: As detailed above; includes flexion tests and potentially diagnostic blocks.
4. Cardiovascular/respiratory: Lung auscultation, heart murmurs (note: flow murmurs are benign in young horses).
5. Orthopedic palpation: Joint effusion, heat, swelling; hoof testers; digital pulses.
6. Imaging: Radiographs of feet (high-motion laminae assessment), knees, hocks (if age/use appropriate). Consider nuclear scan if lameness suspected but localization unclear.
7. Optometry: Fundic exam (cataracts, ERU in certain breeds).
8. Bloodwork: CBC, chemistry, infectious disease screening (EIA, Coggins for interstate transport).

Report format: Objective findings only; avoid prognostication. Document "working soundness" with qualifications.

Breed Predispositions

• Quarter Horses: Hyperkalemic periodic paralysis (HYPP), polysaccharide storage myopathy (PSSM), navicular disease.
• Warmbloods: Laryngeal hemiplegia, stringhalt.
• Arabians/Morgans: Cerebellar abiotrophy, immune-mediated disorders.
• Thoroughbreds: Dorsal metacarpal disease, tendon injuries, exercise-induced pulmonary hemorrhage (EIPH).

Limitations

• Pre-purchase exam findings do not predict future soundness; they document present status.
• Laminitis grading is subjective; serial radiographs are more objective for prognosis.
• NSAIDs carry cumulative toxicity; duration and dose must be individualized.
• Equine orthopedic surgery is specialized; referral is appropriate for complex fractures, joint disease, or refractory lameness.
• Lab reference ranges vary; confirm with sending laboratory.