AAEP Lameness Grading Scale
The AAEP grading scale is the standard system veterinarians use to communicate lameness severity and track treatment progress.
Lameness Localization by Region
AAEP Lameness Grading Scale
| Grade | Description | At Trot | Nerve Block Result |
|---|---|---|---|
| 0 | Sound | No lameness | N/A |
| 1 | Mild | Inconsistent, subtle | Improves lameness |
| 2 | Moderate | Consistent but mild | Marked improvement |
| 3 | Obvious | Clearly observable | Eliminates lameness |
| 4 | Severe | Head nod, hip hike | Dramatic improvement |
| 5 | Non-weight bearing | Cannot trot | Not usually performed |
Lameness Evaluation Protocol
| Observe the horse at walk and trot on a straight line and circle | |
| Note head nod (front limb lameness) and hip hike (hind limb lameness) | |
| Flexion test joints to localize and quantify the lameness | |
| Use hoof testers to identify foot pain (most common source) | |
| Document improvement percentage after nerve blocks | |
| Diagnose lameness yourself — always involve your veterinarian | |
| Work a lame horse — rest until the cause is identified | |
| Assume it's 'just sore' — front limb lameness is always significant | |
| Rush to injections without a complete diagnostic workup |
Over 60% of front limb lameness originates in the foot. A thorough hoof evaluation including hoof testers and diagnostic imaging should be the first step.
Nerve blocks (perineural anesthesia) are the gold standard for localizing lameness. They should be performed systematically from distal to proximal.
The American Association of Equine Practitioners (AAEP) lameness grading scale is a 0--5 numeric scale used by veterinarians to standardize the description and communication of lameness severity in horses. A grade 0 horse is sound; a grade 5 horse cannot bear weight on the affected limb. Understanding this scale helps horse owners communicate with their veterinarians accurately and track the progression or resolution of a lameness condition over time.
| Grade | Description | Recommended Action |
|---|---|---|
| 0–1 | Sound to barely perceptible; inconsistent | Monitor; Grade 1 persisting 2–3 weeks = workup |
| 2–3 | Consistent at trot; obvious on circles/inclines | Veterinary lameness evaluation |
| 4–5 | Marked to non-weight-bearing | Emergency — call vet immediately |
The Five-Grade Scale
Grade 0: No lameness perceptible under any circumstances. The horse moves freely with consistent gait on all surfaces and in all directions.
Grade 1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g., under saddle, circling, on hard surface). A trained eye under specific conditions may detect subtle asymmetry in head bob or hip hike, but it disappears or isn't reproducible. This grade is clinically significant -- a horse that consistently grades 1 on hard surfaces or in circles has a pain source that warrants investigation.
Grade 2: Lameness is difficult to observe at a walk or trotting straight but is consistently apparent under certain circumstances: circling, incline, hard surface, or under saddle weight. Head bob is present but subtle on straight lines; more obvious in circles. This is the most common grade in horses presented for workup -- owners notice something is wrong but may not be certain at a walk.
Grade 3: Lameness is consistently observable at a trot under all circumstances. Head bob is obvious. The horse may be reluctant to trot or will slow significantly. Under saddle, performance is visibly compromised. At this grade, most owners have already recognized a problem.
Grade 4: Obvious lameness with marked head bob, hip hiking, or shortened stride. The horse may walk unevenly. Trotting is reluctant, choppy, and clearly abnormal. The horse bears weight on the limb at rest but moves with apparent pain.
Grade 5: Non-weight-bearing lameness or minimal weight bearing only. The horse cannot use the limb for locomotion. This grade represents severe, usually acute pain -- fracture, severe cellulitis, septic joint, or laminitis founder position.
How Vets Use the Scale
Lameness exams typically include evaluation at walk and trot on both hard and soft surfaces, in straight lines and on circles, and with and without flexion tests. Flexion tests (holding a limb in a flexed position for 60--90 seconds then immediately trotting) can unmask subtle lameness or localize it to a region. Nerve blocks (perineural analgesia) eliminate pain from specific anatomical areas -- a horse that improves by 2 grades after a palmar digital nerve block has a pain source in the caudal foot.
The scale is observer-dependent and has variability between examiners. Some practices use objective gait analysis systems (force plates, inertial sensors) that quantify asymmetry in newtons rather than relying on human observation -- these are increasingly common at referral hospitals and in research settings.
When to Call the Vet
Any new-onset lameness of grade 2 or higher warrants a veterinary evaluation. Grade 4--5 lameness is an emergency. Do not wait to see if it improves if the horse is non-weight-bearing or near non-weight-bearing -- acute structural injuries (fractures, tendon ruptures) become irreversible if not managed promptly. Grade 1 lameness that persists for more than 2--3 weeks also warrants evaluation -- subtle ongoing pain is unlikely to resolve without identifying and addressing the source.
Sources: AAEP lameness scale official publication; Dyson SJ (2011), "Diagnosis and Management of Lameness in the Horse"; Keegan KG (2007) on objective gait analysis, Equine Veterinary Journal; Merck Veterinary Manual equine lameness examination.