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which helps the recognition of pain in ridden horses would be a valuable addition to the veterinarian’s diagnostic armamentarium.
How was the RHpE developed?
Preliminary investigation of ridden horse behaviour evaluated facial expressions (Mullard et al. 2017; Dyson et al. 2017, 2018c), because facial expressions had been proven to be important in pain recognition in the horse (Dalla Costa et al. 2014, 2016; Gleerup et al. 2015; Van Loon and Van Dierendonck 2015) and other species (Cheung and Choi 2008; Langford et al. 2010; Ahola Kohut et al. 2012; Descovich et al. 2017). It was demonstrated that lame and non-lame horses could be differentiated by evaluation of facial expressions alone (Dyson et al. 2017). By examination of video recordings of ridden non-lame
and lame horses an ethogram comprising 117 behaviours encompassing facial expressions, head position and movement, tail movements, body posture and responses to a rider’s cues was developed (Dyson et al. 2018a). The ethogram was applied by an experienced assessor to video recordings of nine horses on two occasions and excellent repeatability was observed. By application of the 117 behaviours ethogram to lame and non-lame ridden horses, 24 behaviours were identified which were seen more often in lame horses, the majority of which were at least 10 times more likely to be seen in horses with musculoskeletal pain compared with non-lame horses. These 24 behaviours make up the RHpE (Table 1, Figs 1–6). The display of ≥8/24 behaviours was highly likely to reflect the presence of musculoskeletal pain, although some lame horses scored <8/24 behaviours. Most non-lame horses scored 0–4 (median 2), whereas the median score for
lame horses was 9 (range 414). Resolution of lameness by diagnostic anaesthesia resulted
in significant reductions in the RHpE scores, consistently to <8/ 24, when the ethogram was applied by an experienced assessor (Dyson et al. 2018b; Dyson and Van Dijk 2020), or by untrained assessors of various professional backgrounds (Dyson and Van Dijk 2020). The latter study identified features of the ethogram which untrained assessors found more difficult to identify, for which training would be beneficial (for example, an intense stare [Figs 1a, 3a, 4b, 5b], the bit being pulled through to one side [Figs 1b, 3a]). In addition, a threshold of 6, 7, 8 or 9 behaviours for differentiation between non-lame and lame horses was tested, and 8/24 behaviours had the highest combined sensitivity (0.86) and specificity (0.80) compared with 6 (sensitivity 0.95, specificity 0.65), 7 (sensitivity 0.92, specificity 0.72) and 9 (sensitivity 0.81, specificity 0.80). The substantial reduction in RHpE scores after resolution of pain by diagnostic anaesthesia validated a causal relationship between pain and alterations in behaviour.
How has the RHpE been validated?
All the initial development and testing of the RHpE used video recordings. However, comparison between video assessment and real-time application of the RHpE showed excellent agreement for a trained assessor (Dyson et al. 2020b). The ability of a cross-section of equine veterinarians of variable age, sex and experience to apply the RHpE in real-time, after preliminary training, was tested by
TABLE 1: The Ridden Horse Pain Ethogram, adapted from Dyson et al. 2018a
1. Repeated changes of head position (up/down), not in rhythm with the trot
2. Head tilted or tilting repeatedly 3. Head in front of vertical (>30°) for ≥ 10 s 4. Head behind vertical (>10°) for ≥ 10 s 5. Head position changes regularly, tossed or twisted from side to side, corrected constantly
6. Ears rotated back behind vertical or flat (both or one only) ≥5 s; repeatedly lay flat
7. Eye lids closed or half closed for 2–5 s; frequent blinking 8. Sclera exposed repeatedly 9. Intense stare (glazed expression, ‘zoned out’) for ≥ 5s
10. Mouth opening shutting repeatedly with separation of teeth, for ≥ 10 s
11. Tongue exposed, protruding or hanging out, and/or moving in and out repeatedly
12. Bit pulled through the mouth on one side (left or right), repeatedly
13. Tail clamped tightly to middle or held to one side 14. Tail swishing large movements: repeatedly up and down/ side to side/ circular; repeatedly during transitions
15. A rushed gait (frequency of trot steps > 40/15 s); irregular rhythm in trot or canter; repeated changes of speed in trot or canter
16. Gait too slow (frequency of trot steps < 35/15 s); passage- like trot
17. Hindlimbs do not follow tracks of forelimbs but repeatedly deviated to left or right; on 3 tracks in trot or canter
18. Canter repeated leg changes in front and/or behind; repeated strike off on wrong leg; disunited
19. Spontaneous changes of gait (e.g. breaks from canter to trot, or trot to canter)
20. Stumbles or trips more than once; repeated bilateral hindlimb toe drag
21. Sudden change of direction, against rider’s cues; spooking
22. Reluctance to move forwards (has to be kicked verbal encouragement), stops spontaneously
23. Rearing (both forelimbs off the ground) 24. Bucking or kicking backwards (one or both hindlimbs)
Assessments are made in walk, trot (to include 10 m diameter circles in rising trot), canter and transitions on both the left and right reins, and in more advanced movements requiring collection in horses which are trained to do so. A total behaviour score of ≥8 (out of 24) is likely to indicate the presence of musculoskeletal pain. S, seconds
the evaluation of 20 horse-rider combinations performing a purpose-designed dressage test of 8.5 min’ duration (Dyson et al. 2020b). The volunteer riders considered that their horses were capable of working comfortably, ‘on the bit’ at trot and canter for 30 min. The gait of the horses was assessed independently by another experienced equine clinician, who determined the presence of lameness and/or abnormalities of canter. By application of the RHpE alone, the trained veterinarians were able to differentiate horses with low-grade lameness (the most frequent lameness grade was 2/8 [Dyson 2011]) and abnormalities of canter and non-lame horses, with good agreement with an experienced assessor. The RHpE was further tested by use in the field. Data from
the 20 horses described in Dyson et al. (2020b) were combined with data from the evaluation of a convenience sample of a further 40 horses in regular work and presumed
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