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and non-trained assessors from a variety of equine-related professions (Dyson and Van Dijk 2020).
How to use the RHpE
What you need to know before using the RHpE The assessor needs to be fully aware of the definitions of each of the 24 behaviours (Table 1, Figs 1–6), and the use of a check sheet (Supplementary Item 1) is strongly advised. Certain factors need to be assessed before the RHpE is applied. Some arena surfaces are very deep, and all horses appear to disturb the footing with their hind feet, making it difficult to determine accurately if the horse has a bilateral hindlimb toe drag. If the bit is too wide, then the bit will appear that it is being pulled through to one or both sides of the horse’s mouth. Some horses have a small iris in one or both eyes, so the sclera can be seen at rest, so repeated exposure of the sclera cannot be counted as a pain behaviour in one or both eyes of these horses. If the muzzle is pink (Fig 6b) it may make it more challenging to determine if the mouth is open.
Timing, work pattern, duration and intensity After a short period of warm-up following the rider’s usual protocol, the horse should be worked in walk, trot and canter on both reins around the periphery of the arena, and should be observed from both sides, the front and the rear (Fig 1–6). In a rectangular arena it is best to watch the horse from two different corners, on the left and right reins, respectively. It is important to view the horse from behind as well as from both sides and from the front on both reins. Ideally the horse should also be observed performing 10 m diameter circles in rising trot, to the left and right, as figures of eight. Some horses are completely comfortable being ridden in working paces and may only show discomfort when working in collection in specific movements. It is therefore important to observe the horse performing its full repertoire of movements. The horse should be observed for a minimum of 5 min and up to 10 min. Some of the behaviours are defined as being time dependent (for example, ears behind vertical for ≥5 s) and their duration should be timed using a stopwatch. An assessor has to be aware of how a rider is applying cues to the horse. For example, tail swishing may coincide with application of a spur aid (Fig 1a), rather than occurring spontaneously, and therefore should be disregarded unless repeated under other circumstances. It must be borne in mind that several of the definitions state ‘repeated’, for example repeated incorrect strike off into canter, repeated exposure of the sclera; a single occurrence of such a behaviour would not fulfil the criteria of the ethogram.
Training As with any clinical skill, training and practice are essential for accurate interpretation of the RHpE and improvements in performance with training have been demonstrated (Mullard et al. 2017; Dyson et al. 2020b). An on-line training course is available1, although the effectiveness of this training course has not been scientifically validated.
Factors that can potentially influence the RHpE
A RHpE score ≥8/24 is likely to reflect the presence of musculoskeletal pain, but to date no relationship between
the RHpE score and the source(s) of pain has been determined. Rider size may also influence the RHpE score. In a cross-over design study, four riders of varying size rode six horses in randomised order, performing a standardised dressage-type test (Dyson et al. 2018d, 2020a). There was a significant positive correlation between rider weight and the RHpE score, although the majority of scores were <8/24. Saddle fit for both the horse and the rider are potential
influential factors on RHpE scores (Dyson et al. 2018d, 2020a). In a few small studies an ill-fitting saddle, considered by a Society of Master Saddlers Qualified Saddle Fitter to have the potential to adversely affect performance, did not have a statistical influence on RHpE scores (Dyson and Pollard 2020; Dyson et al. 2020b, 2020c). However, in a much larger scale
study, saddles with tight tree points compared with correctly- fitted saddles and riders seated at the back of the saddle rather than the middle were associated with significantly higher RHpE scores (Dyson et al. 2022a). This is consistent with previous clinical observations that there have been dramatic improvements in RHpE scores and gait in some horses after change from a saddle with excessively tight tree points to a better fitting saddle (Dyson et al. 2020b). However, if an underlying lameness is also present, abnormal behaviour will persist.
Rider skill has the potential to influence the quality of a
horse’s gait. When the performance of 40 horses was assessed, each ridden by two different riders, a professional rider and the horse’s usual rider, there was a significant correlation between rider skill scores and gait quality scores (Dyson et al. 2020c). The presence of lameness or gait abnormalities in canter, when ridden by each rider, varied among horses. However, there was no significant effect on the total RHpE scores when horses were ridden by their usual riders compared with the professional rider. Nonetheless, some individual behaviours did change. Thus, a more skilled rider may make a horse move better compared with a less skilled rider but will generally be unable to conceal behavioural signs of musculoskeletal pain, although the specific behaviours exhibited may change. There is considerable controversy about the use of
potentially restrictive nosebands (Fenner et al. 2016; Doherty et al. 2017; Uldahl and Clayton 2019) and the use of a bit as opposed to a bitless bridle (Cook and Kibler 2019; Mellor 2020). In a study of 148 ridden horses, those wearing crank cavesson nosebands compared with cavesson nosebands had significantly higher RHpE scores, but there was no effect of other noseband types (Dyson et al. 2022a). There was no difference in mouth opening, as defined by the RHpE (Figs 1b, 4d), in horses with a noseband with the potential to restrict mouth opening, compared with a correctly-fitted cavesson noseband, or no noseband. In lame horses, diagnostic anaesthesia resulting in resolution of lameness was associated with substantial reductions in RHpE scores, despite the presence of a bit and potentially restrictive nosebands (Dyson et al. 2018b; Dyson and Van Dijk 2020). However, the proportional reduction in the frequency in occurrence of mouth opening with separation of the teeth for ≥10 s, was less than for some other behaviours (Dyson and Van Dijk 2020). Mouth opening with separation of the teeth for ≥10 s was commonly observed in horses warming up for the dressage phase of 5-star three-day events, the majority of which wore potentially restrictive nosebands (Dyson and Ellis 2022).
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