When “Sound” Isn’t Simple

The trot-up at a three-day event has become as popular as the competition itself and is watched with as much scrutiny from the side-lines as from the officials. Owners, riders, vets, journalists and spectators may all have an opinion on whether a horse looks sound, stiff, short-striding or simply fresh and excited. Yet the decision does not rest with the crowd: it's the responsibility of the Ground Jury, advised by the veterinary delegate, to decide whether each horse is fit to start or continue the competition. With so much at stake for performance, welfare and public confidence, is it time to review how horse inspections are carried out?

In this next instalment of Sue's Snippets of Science series, I will try and answer this question and look at whether an asymmetrical gait is of clinical significance in elite event horses by looking at some of the research out there.

There's lots of discussion about mandatory horse inspections at three-day events and the subjective nature of gait assessments.

The role of these inspections is to determine the suitability of a horse to start or complete the competition. If you have ever watched one of these inspections, it's sometimes unclear to onlookers why one horse is passed and another, following referral to the holding box and subsequent reinspection, is failed.  This really opens up the discussion and questions the accuracy of the assessment of a fit, potentially excited horse trotted up once in each direction.  In addition, there's evidence that horses may appear non-lame in-hand and pass an inspection, but exhibit lameness when ridden.

In a Swiss based study 33 event horses competing at 3* or 4* level underwent objective gait analysis to assess symmetry of movement of the poll, withers and pelvis [1] before the cross-country phase and one day after. In contrast to conventional horse inspections, the horses were trotted up at least four times over 50m to achieve at least 25 strides of steady state trot.

The asymmetry values were compared with predetermined thresholds which are used to differentiate lame and non-lame horses. All horses were also assessed subjectively, independently from the study.

All horses were judged subjectively as fit to compete at both the first and second inspections.

A total of 58% (before cross-country) and 77% (after cross-country) of the 33 horses exhibited gait asymmetries that exceeded published lameness threshold values, respectively. The magnitude of pre-existing gait asymmetries was not significantly increased after the cross-country phase. However, overall, stride duration was shorter at the second inspection compared with the first.

These results indicate that the introduction of objective gait analysis at horse inspections may create confusion. What threshold values should be used to constitute a ‘fail’ if a large proportion of competitors have asymmetry values above the predetermined values for the presence of lameness? How accurate are these thresholds? Did the horses which had asymmetry values above the threshold for lameness have a pain-induced asymmetry and if that was the case why was there no difference after a strenuous test? Could the horses have performed better if they were more symmetrical?  Does pre-existing asymmetry potentially predispose to the development of subsequent injury? From a risk of exacerbation of injury and a horse welfare perspective, is a horse that develops asymmetry at the second inspection more at risk than those that started with asymmetry outside the threshold?  Are there greater risks for forelimb versus hindlimb asymmetries?

These are all unanswered questions, but this small study highlights the potential limitations of utilising objective gait analysis at horse inspections.

Additionally, a French based study of 12 horses considered non-lame by the owners demonstrated that within individual horses there were variations in the magnitude of measurable asymmetries within several examinations performed on one day and among examinations performed on different days [2].

The shortened stride duration at the second inspection could reflect a pain-induced gait modification of movement, but any bilaterally symmetrical change in movement patterns will not be detected by the current methods of objective gait analysis and is also likely to be overlooked by the Ground Jury.

In conclusion, it appears that the value of the current thresholds for differentiation of lame and non-lame horses using objective gait assessment may not be sufficiently accurate for determining fitness to compete. Therefore, despite the limitations of subjective gait analysis, perhaps it is the best tool currently available.

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References

1.      Scheidegger, M.,  Gerber, V., Dolf, G., Burger, D., Axiak Flammer, A.,  Ramseyer, A.  Quantitative Gait Analysis Before and After a Cross-country Test in a Population of Elite Eventing Horses.  J. Equine Vet. Sci. 2022, 117: 104077.    doi:10.1016/j.jevs.2022.104077

2.      Hardeman, A., Serra Bragança F., Swagemakers, J.H., Van Weeren, P.R., Roepstorff, L.  Variation in gait parameters used for objective lameness assessment in sound horses at the trot on the straight line and the lunge. Equine Vet. J. 2019, 51: 831–839. doi: 10.1111/evj.13075