Equine Medicine

Equine Medicine

Overview

Equine-specific clinical medicine addressing the unique physiology of hindgut fermenters, performance demands, and acute vs. chronic disease patterns. Horses are continuous grazers dependent on stable cecal microbiota; disruptions cause colic and acidosis. Colic is the leading cause of equine mortality and requires rapid triage. Laminitis is the second-leading cause of euthanasia and demands grading, digital thermography, and radiographic assessment. Lameness evaluation requires systematic flexion tests and nerve blocks. NSAIDs (phenylbutazone, flunixin meglumine) are critical analgesics but carry GI and renal risks. Metabolic diseases (PPID, equine metabolic syndrome, laminitis) are increasingly diagnosed. Pre-purchase examinations require a structured framework. Age and breed predispositions shape disease risk and treatment approach.

When to Use

• User presents a case or question involving equine medicine
• User asks about colic triage, classification, or management
• User discusses laminitis grading (Obel) or acute vs. chronic phases
• User questions lameness evaluation or diagnostic techniques
• User asks about NSAIDs, Cushing's disease (PPID), or metabolic syndrome
• User requires pre-purchase exam framework or documentation
• Keywords: horse, equine, foal, colic, laminitis, lameness, flexion test, nerve block, PPID, Cushing's, metabolic syndrome, phenylbutazone, flunixin, hindgut

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.