The Lameness Debate in Horses - Subjective Judgement vs Objective Measurement

Science has the power to transform the way we care for, ride and manage our horses, but let’s be honest, research papers can often feel like a foreign language and if you've ever tried to read one and ended up more confused than when you started - you’re not alone!

The world of equine research is full of fascinating discoveries, but it’s not always easy to work out what they actually mean for you and your horse. That’s why we’re thrilled to announce a brand-new series of online articles with world-renowned equine veterinarian and researcher, Dr Sue Dyson.

In Sue’s Snippets of Science, Sue will cut through the jargon and bring you clear, practical insights from the latest equine studies – turning complex data into knowledge you can actually use in your daily life with horses. Each edition will break down a key piece of research, sharing what it really means for horse owners, riders, and professionals, as well as highlighting any limitations so you can make informed decisions.

We’ll be sharing up to six articles a year, so you can look forward to regular, easy-to-digest updates that will help you understand your horse better – without the headache of reading pages of scientific jargon.

In this first article, Sue delves into the subject of gait asymmetry in trot and whether it’s always a sign of pain.

There is considerable discussion about the subjectivity of lameness assessments and the potential value of objective methods of measuring gait asymmetry at the trot. However, it’s not known to what extent measurable asymmetry equates with pain-related lameness.

At endurance races, horses are subjected to repeated mandatory veterinary inspections and are evaluated moving in-hand on a firm level surface at trot, over approximately 40m there and back, being examined as the horse trots away and as it returns. The official endurance veterinarian is making a judgement as to whether a horse is fit to continue in the competition, or at the end if it can be classified as finishing in a fit state to permit completion. Horses are assigned a grade according to FEI regulations: A = sound, B = mild asymmetry and C= severe asymmetry, with C being a cause for elimination.

Clearly there’s a lot at stake, with a high onus of responsibility on the official endurance veterinarian to accurately select those horses which are not fit to continue and not eliminating a horse which is potentially fit to continue. The questions are whether objective gait analysis can do better than subjective evaluation and to what extent there is agreement between subjective and objective assessments.

In a recent study based in Italy a total of 110 horses were recruited from three endurance competitions (de Chiara et al. 2025). While the experienced official endurance veterinarian carried out his examinations, video footage was collected from the opposite end of the trot up for subsequent analysis using the artificial intelligence (AI) motion tracking system (AI-MTS), marketed as SLEIP.

Using statistical analysis, the agreements between the subjective and objective gait analyses were calculated. A perfect agreement would be a score of 1.  There was substantial agreement (0.75) for severe lameness, but only fair agreement (0.25) for no asymmetry and no agreement (0.13) for mild asymmetry.

SLEIP indicated no asymmetry in eight horses, but the official endurance veterinarian deemed them asymmetrical, three with forelimb asymmetry, three with hindlimb asymmetry and two with both forelimb and hindlimb asymmetry.  In 2% of horses the SLEIP analysis would have resulted in elimination of these horses but based on the assessment by the official endurance veterinarian, the horses were allowed to continue and did complete. Among the horses categorised as mild asymmetry there was disagreement between the subjective and objective analyses in 16%.

There is an increasing body of evidence that there is potential overlap in asymmetry ranges for horses apparently working comfortably and those with pain-related lameness. Moreover, there are some horses with lameness-induced poor performance in which there is minimal asymmetry when evaluated moving in-hand.  This means that the results of objective lameness evaluation need to be considered with great care. It seems that in this Italian study there was good agreement for the easy cases – those with severe lameness – but not for the other horses.

The Take Home Points

The authors concluded that ‘The AI-MTS can be a helpful and objective aiding tool for official endurance veterinarians’ decision-making when performing visual lameness assessment during endurance competitions, particularly in cases of mild lameness, which is known to be the most challenging to identify.’ However, this does not appear to represent their findings because overall there was no agreement between the objective and subjective assessments for mild lameness, the most challenging category.

This highlights the need to carefully evaluate the design of a scientific study, the interpretation of the results and the conclusions drawn by the authors.

Objective lameness assessment does not solve all the problems, but for serial monitoring of an individual horse it can be a potentially excellent tool, and for comparing gait before and after nerve blocks by removing the potential bias of the observer.

Expand Your Knowledge Further

Sue is one of the keynote speakers at the Horses Inside Out Conference in February 2026. The conference runs for three days (21 - 23 February) and the theme is Soundness and Symmetry: Advancing Welfare Optimising Performance.

She will be presenting - Determining Acceptable Asymmetry vs Unacceptable Lameness.

Drawing on her extensive clinical experience and research, Sue will explain how to distinguish between natural variations in movement and signs of underlying pain or dysfunction. This session will provide practical guidance for riders, vets, and therapists on recognising when asymmetry is a normal part of a horse’s biomechanics and when it signals a need for further investigation.

Conference 2026 PHYSICAL ATTENDANCE

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References: De Chiara, M., Montano, C., De Matteis, A. et al.  Agreement between subjective gait assessment and markerless video gait-analysis in endurance horses. Equine Vet. J. 2025; doi:10.1111/evj.14516