The AAEP Horse Lameness Scale Explained

Lameness—defined as any alteration in the horse’s normal gait—negatively affects:

  1. A horse’s ability to perform and compete;
  2. The horse-rider bond;
  3. The horse’s welfare; and
  4. The owner’s finances.

Thus, addressing lameness is an important aspect of a veterinarian’s role in equine practice.

“Lameness presents in a number of ways, including a change in behavior such as an unwillingness to jump, move forward, and collect, as well as changes in balance, limb motion, and weight-bearing,” explained Nicola Cribb, MA, VetMB, DVSc, Dipl. ACVS. Cribb is a large animal surgeon and adjunct faculty at the University of Guelph’s Ontario Veterinary College. She has worked with lame horses from a range of disciplines and backgrounds in Canada.

Lameness, especially subtle gait abnormalities, can be challenging to recognize despite the array of diagnostic tools available to practitioners. Veterinarians not only need to identify whether a horse is lame but also pinpoint the exact location and structures involved in causing the horse pain, ergo lameness.

“My typical lameness examination involves evaluation of the standing horse, then watching the horse walk and trot in a straight line, in circles, and on soft and hard surfaces,” said Cribb.

Identifying and grading a lame horse based on the initial examination provides a solid baseline to begin additional testing.

“For example, if the horse is a Grade 3 lame on the right front while trotting, does the lameness improve after using diagnostic anesthesia to block (numb) the foot or knee?” Cribb said. “Grading the lameness will also help determine if the proffered treatment has helped the horse or not when reevaluated.”

In North America veterinarians predominantly use this 5-point scale described by the American Association of Equine Practitioners:

  • 0: Lameness not perceptible under any circumstances.
  • 1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g., under saddle, circling, inclines, hard surface, etc.).
  • 2: Lameness is difficult to observe at a walk or when trotting in a straight line but consistently apparent under certain circumstances (e.g., weight-carrying, circling, inclines, hard surface, etc.).
  • 3: Lameness is consistently observable at a trot under all circumstances.
  • 4: Lameness is obvious at a walk.
  • 5: Lameness produces minimal weight-bearing in motion and/or at rest or a complete inability to move.

“That said, the AAEP Lameness Scale, like similar lameness scales, are subjective in nature, leaving much up to the veterinarian’s professional opinion,” Cribb said. “This means that not all veterinarians will always agree on what grade lameness to assign to the same patient.”

One study showed experienced veterinarians agreed that a forelimb or hind limb was lame more than 9 out of 10 times when the lameness was graded over a 1.5. However, when the lameness was subtle, less than 1.5, the veterinarians only agreed about 66% of the time for a forelimb lameness and 50% of the time for a hind-limb lameness (Keegan et al. Equine Veterinary Journal 2010).

“Nonetheless, the AAEP Lameness Scale still provides a means for necessary documentation of the lameness and allows veterinarians to consistently use the same system to grade lame horses, leading the way for better care,” said Cribb.