In 2012 it was estimated that there were at least 840,000 horses in Great Britain [1
]. There is limited information available about the frequency of occurrence of lameness and other sources of musculoskeletal pain in sports horses and riding school horses. In the United Kingdom’s Blue Cross National Equine Health survey for 2018, lameness accounted for 23% of all disease syndromes reported for 13,873 horses [2
]. However, there is evidence that owners and trainers are poor at lameness recognition; in a United Kingdom survey of 506 sports horses in full work and presumed to be non-lame, 47% were lame or had other pain-related gait abnormalities [3
]. In a Swedish study of sports horses in full work and functioning normally, 53% of 201 horses showed measurable asymmetry of gait when trotted in hand [4
In order to facilitate the recognition of musculoskeletal pain in ridden horses, a Ridden Horse Pain Ethogram (RHpE) was developed, comprising 24 behaviours, the majority of which were at least 10 times more likely to be seen in a lame horse compared with a non-lame horse [5
]. Reduction in RHpE behaviour scores, after diagnostic anaesthesia had abolished lameness, verified a causal relationship between the behaviours and pain [6
]. The display of eight or more behaviours of the RHpE is likely to reflect the presence of musculoskeletal pain [5
]. Previous work has focused on comparisons between non-lame horses and horses undergoing veterinary investigation of lameness or poor performance.
Veterinarians, after appropriate training, were able to predict the presence of musculoskeletal pain by application of the RHpE [8
]. Other factors which may potentially influence the results of applying the RHpE include an ill-fitting saddle [9
], rider size (influenced by height, weight and saddle fit for the rider) [10
] and rider skill [13
The aim of the current study was to further test the RHpE by its application to a convenience sample of sports horses and riding school horses in regular work and assumed by their owners to be working comfortably. It was hypothesised that there would be a positive association between the RHpE behaviour score and the presence of lameness and/or gait abnormalities in canter.
In accordance with our hypothesis there was a positive association between RHpE scores and the presence of lameness and, given the results of previous studies [6
], this is likely to be a causal relationship. However, contrary to our hypothesis, gait abnormalities in canter, either alone or in combination with lameness, although carried forward to the multivariable analysis, were not significant in the final model. In addition, rider skill score was negatively associated with the RHpE score. However, this may not be a causal relationship. Although work discipline was not retained in the final model, this is probably because riders of the Riding School horses, which had the highest median RHpE score, had the lowest median rider skill score from all the work disciplines.
There are several studies which demonstrate that unskilled novice riders have a less stable position and lack of phase synchrony with the horse compared with riders of superior skill and experience [21
]. These features have the potential to alter the horse’s head and neck position [25
], lameness [26
], and quality of gaits [27
]. However, we have previously observed during clinical investigation of lame horses that, when ridden by a skilled professional, the rider may appear to ride relatively poorly. However, when gait abnormalities are abolished by local anaesthesia, the rider then appears to be both more in harmony with the horse and considerably more proficient. Moreover, 40 of the horses in the current study were part of a related study in which all horses were ridden by the normal rider and a professional rider [28
]. The professional rider’s skill score ranged from 3.5 to 7/10 (median 6), being strongly influenced by the presence (low rider skill score) or absence (high rider skill score) of lameness [28
]. In a study involving eight riders, four beginners and four more experienced riders, and eight riding school horses there was no effect of rider skill on a limited number of horse behaviours [13
]. As might be expected, in the current study rider skill level was higher for horses used for affiliated level competition compared with General Purpose and Riding School horses, but overall the median score was low (4.75/10), corresponding to less than sufficient as defined by the Fédération Equestre Internationale [18
]. It remains possible that an unskilled rider riding a pain-free horse may alter its behaviour.
There was a high frequency of low-grade (≤ grade 2/8 [14
]) lameness (73%) and other gait abnormalities (47%) in the current study, reflecting owners’ inability to recognise musculoskeletal pain, as previously documented [3
]. It should be borne in mind that in horses with lameness in more than one limb, as frequently observed in the current study, the grading of lameness may be neither accurate nor reflect the level of discomfort [14
]. Education of riders and trainers about the value of the RHpE for detecting the likely presence of musculoskeletal pain may prompt them to seek professional advice. Lameness was not necessarily a continuous feature, but was often accentuated in 10 m diameter circles in trot, highlighting the value of this exercise when investigating poor performance and at pre-purchase examinations. The test performed by the riders was purpose-designed to include 10 m diameter circles because it has previously been observed that this movement can influence both lameness and behaviour [6
]. This study also reinforces the importance of evaluating the quality of canter, which may be compromised especially in association with hindlimb lameness or sacroiliac joint region pain [17
]. Although gait abnormalities in canter were not significant in the final model, it does not mean that such abnormalities are not of biological significance. It has previously been observed, in a minority of horses, that no behavioural or gait abnormalities were detectable in trot, whereas gait abnormalities in canter were seen in association with a high RHpE score [6
Of the Riding School horses 9/11 (82%) showed lameness and 6/11 (55%) displayed gait abnormalities in canter; only one horse was graded as displaying no gait abnormalities, but this horse worked consistently with the front of the head in front of the vertical > 30° ≥10 s and had reduced range of motion of the thoracolumbosacral region, and had a RHpE score of 13. Overall, the median RHpE score for the Riding School horses was higher than for the other work disciplines. There are limited published data concerning riding school horses. In a Swedish study of 99 horses from eight riding schools, 15 exhibited ‘moderate lameness’ in hand or on the lunge, including eight with gait abnormalities in canter [33
]. However, ‘irregular movement’ (presumably low-grade lameness) was observed in an additional 45 limbs and a further 17 horses were described as ‘moving short’ and nine ‘moved flat on the ground’. Thus, potentially up to 87% of the horses had gait abnormalities reflecting musculoskeletal pain. In a cross-sectional study of 2566 Dutch riding horses from 150 horse farms, 19.3% were lame or had ‘irregular locomotion’ when assessed moving in hand by trained veterinary students [34
]. Riding school horses had a higher risk of lameness than horses used for recreation or competition. The sample size of Riding School horses in the current study was small, but if it is representative of the United Kingdom Riding School population, the high incidence of lameness and RHpE scores ≥8 is of cause for concern. Under the Riding Establishments Act (1964) horses have to undergo a statutory annual veterinary inspection to determine that they are ‘in all aspects physically fit’. This examination does not require horses to be ridden. Education of riding school proprietors about the RHpE and the use of ridden exercise and application of the RHpE by veterinarians during their inspections may enhance riding school horse welfare.
The RHpE scores ranged from 3 to 16/24, with a median of 9. These scores were substantially higher than those documented at three 5* three-day events during warm-up for the dressage phase, at which the scores of 172 horses ranged from 0 to 9 (median 4) [35
]. In the latter studies, horses with a score ≥7/24 performed significantly less well in the dressage and cross-country phases and had lower overall places, compared with horses that scored <7. In the current study, with the exception of one Riding School horse and one General Purpose horse, all non-lame horses that had a normal canter had a RHpE score <8 (range 3–6, median 5), consistent with previous reports [5
]. This reinforces that a RHpE score ≥8 is likely to reflect musculoskeletal pain. We have previously demonstrated through assessment of sensitivity and specificity that a threshold of 8 is appropriate for the differentiation of horses with and without musculoskeletal pain [7
]. It was clear that riders, irrespective of their skill level and experience, had a lack of recognition of the behavioural signs which may reflect musculoskeletal pain. We believe that many riders learn to ride on riding school horses which exhibit these signs, so that there is a generalised acceptance that these behaviours are normal for horses. There is an urgent need for education of riders and trainers at all levels to recognise that demonstration of eight or more behaviours of the RHpE is highly likely to reflect musculoskeletal pain.
Overall, the incident rate of each of the RHpE scores for lame horses was 1.27 times the incident rate for the non-lame horses. Those features which had the strongest relationship with lameness were ears back for ≥ 5 s, an intense stare for ≥ 5 s, and repeated stumbling or bilateral hindlimb toe drag, similar to previous observations [7
]. Although these associations were not retained following adjustment for multiple comparisons, this likely reflects the limitations of the sample size and the variation with which individual horses show pain-related behaviours. As previously documented [5
] and as illustrated in Table 2
, different horses show different behaviour patterns and therefore reliance on a limited spectrum of behaviours is potentially misleading.
In the current study the presence of thoracolumbosacral epaxial muscle pain or increased muscle tension did not influence the RHpE score. Although palpation is a subjective assessment, there is evidence that it may be more reliable than more objective assessments [37
]. There is a relationship between the presence of either lameness [38
] or sacroiliac joint region pain [32
] and epaxial muscle hypertonicity and pain. We have observed that when pain associated with lameness or sacroiliac joint region pain is abolished using local anaesthesia, there is a substantial reduction in the RHpE scores, despite the persistence of epaxial muscle hypertonicity or pain [6
], which is consistent with the results of the current study.
There was a disturbingly high proportion (47%) of ill-fitting saddles with the potential to adversely influence performance. However, in the current study, saddle fit did not influence the RHpE score. Nonetheless, a change from an ill-fitting saddle to a better fitting saddle may have a dramatic influence on ridden horse behaviour [39
]. Twenty-one horses were assessed ridden by a single professional rider in both a well-fitting saddle and an ill-fitting saddle [40
]. There was significantly less variability in gait with the better-fitting saddle compared with the ill-fitting saddle. It is therefore considered important to address saddle fit when assessing a horse with poor performance. If a high RHpE score persists after abolition of lameness using diagnostic anaesthesia this usually indicates the presence of an additional problem, such as an ill-fitting saddle, meriting further investigation [7
A small proportion (3%) of horses that had a RHpE score of ≥8 did not show overt lameness or gait abnormalities, as defined, in canter. There are other gait variants which are likely to reflect adaptations to musculoskeletal pain which are not covered by the conventional understanding of lameness, the definitions employed for this study, or behaviours within the ethogram. These include a short stepping forelimb gait; reduced range of motion of the thoracolumbosacral region; reduced flexion of the lumbosacral joint; ‘on the forehand’; scooting forwards episodically; ‘jumping’ into transitions to trot from walk; transiently going above the bit in upward transitions; stepping short on the hindlimbs in downward transitions from canter to trot, or from trot to walk; ‘croup high’ in canter; and altered movement of the thoracolumbar region in canter resulting in rotation of the rider’s pelvis [15
]. It is therefore suggested that it is crucial to apply the RHpE to horses performing both trot and canter and also to observe behaviour and movement quality in transitions between gaits.
An inherent limitation of the study design is that the trained assessor who applied the RHpE could not be blinded to the lameness status of the horse, work quality or the skill of the rider. Assessment of epaxial muscle tension or pain, saddle fit, lameness and canter, and rider skill were all subjective, but were performed by independent experts, with no knowledge of the RHpE scores. Quantitative assessment of ridden horse gait [43
] has many limitations, especially in a horse lame on more than one limb, and for lameness that varies between reins and different movements, and cannot be used to assess transitions between gaits or canter. The gait may alter between rising and sitting trot and vary depending on the diagonal on which the rider sits [15
], however, in the current study all trot work was performed in rising trot, because the majority of the riders rarely rode in sitting trot. Riders sat on the correct diagonal, when the outside forelimb and inside hindlimb were bearing weight. There are other potential confounders that were not identified or measured in the current study. For example, although bit fit was assessed, the mouth was not inspected, so the presence of oral lesions that could have contributed to discomfort cannot be excluded. Noseband type and fit were recorded, but not included in the analyses. Poisson regression generally requires a large sample size, so it is likely that our model did not have sufficient power to detect more subtle associations. However, the results of the Poisson regression reflected the results of the pairwise comparisons and allowed us to fully utilise the data and to assess the effect of multiple variables on RHpE scores in the same model. The study population was a convenience sample and may not be representative of the United Kingdom horse population as a whole.
There has been limited comparison between physiological markers of stress and ridden horse behaviour [44
]. In a previous review of ridden horse behaviour, the difficulties of differentiation between behaviour reflecting pain, anxiety, fear and mental state were highlighted, together with the potential overlap between physiological signs of stress and the response to physical exertion [45
]. The RHpE appears to provide a simple method of determining the likely presence of musculoskeletal pain, with the current study providing further evidence of the strong association between a RHpE score ≥8 and the presence of lameness.