Let’s discuss the critical topic of pain recognition in horses and whether you can diagnose any of the above conditions based on their behaviour.
What happens with the stimulation of the sensory receptors is fairly well understood. That being the mechanism of how signals are transmitted through the body via neurological pathways, and the process of when it is received by the central nervous system. Well, at least at a basic level – there’s plenty more to be learnt! However, the underlying physiology is the same for humans and for horses.
What differs is the perception of pain, both between species and individuals. People can verbally express and reason pain, its causes and hopefully use logic to either actively or passively manage it. Pain is an ‘unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage’, and understanding this aids cognitive strategies and choices to express or manage it. Based on our understanding of the horse’s brain, there is less reasoning, reflecting and planning likely to be occurring.
There are, however, some similarities in the ways pain can be ‘read’ in a non-verbal human and the horses because we know that the induction of pain causes changes in behaviour. Post-surgery facial expressions in horses demonstrate consistent patterns in those not given pain relief, and induction of pain via chemical mediators also affects positions of ears, eyes and the muzzle [1, 2]. It has been consistently shown that behaviours demonstrated by horses when ridden can be linked to musculoskeletal pain [3].
Knowing that the horse demonstrates pain via facial and body language is very important to those that care for horses. We should be on the lookout for any signs of pain, however subtle. But can the behaviours shown by a horse in pain, tell you where the pain is coming from?
There are plenty of social media posts that talk of absolutes – that X always equals Y – but others that will tell you that X definitely does not equal Y. So when it comes to pain behaviours, there is a very clear pattern that it is not as simple as either of those extremes. It might seem obvious to some, but I think this message needs reinforcement.
There are long lists of signs of kissing spines in the ridden horse; reports by many authors researching diagnosis and treatment of the disease, ranging from poor performance, poor jumping, ill-defined hindlimb lameness, bucking and resistance to saddling-up [4]. Presenting complaints include poor ridden performance, manifest as either pain or distress during riding, inconsistent shifting, lameness only apparent under saddle, reticence or poor jumping performance. An inability to build or maintain epaxial muscle mass was sometimes present [5]. Complaints of poor performance under saddle ranged in severity from inability to maintain a particular lead while cantering to violent objection and incessant bucking that rendered the horse unsafe for ridden exercise [6]. The presenting clinical signs and primary owner complaints described included rearing (n = 3), bucking (n = 15), reluctance to go forward (n = 9), poor performance (n = 15), aggressive behavior (n = 6), tension, stiffness, and reduced flexion (n = 19), bolting (n = 3), combinations of the above (n = 25), and other reasons (n = 7) [7].
Another commonly presenting pathology in sports horses is equine gastric ulcer syndrome with different groups of sports horses reported as having 51-100% horses reported to be affected. In a study investigating behaviour that could be related to EGUS one vet practice reviewed data from 37 horses presenting with ‘girthiness’ [8]. Girthiness manifested as a range of behaviours flattening of the ears, swishing of the tail, biting, moving away, humping the back, and other general signs of discomfort or avoidance. From the initial 37 horses, 13 underwent gastroscopy with 12/13 being diagnosed with gastric ulceration. Resolution of the clinical signs observed (girthiness) was accomplished in all horses (12/12) after treatment by veterinary medical care. The change in signs were according to owner’s feedback, which is a limitation due to the risk of subjective bias however, not all were re-scoped. Interestingly, a further 10 horses were diagnosed with orthopaedic issues as the most probable cause of discomfort. The diagnoses included thoracic and lumbar vertebral osteoarthritis (4), cervical vertebral osteoarthritis (3), bone spavin (2), front limb lameness (1) and a further three of 37 horses had back pain, which was attributed to an ill-fitting saddle [8].
The conclusion was that girthiness is a nonspecific clinical sign that could be caused by multiple conditions. The recommendation is that a complete physical and lameness examination, including saddle fit evaluation, should be performed in all horses to rule out painful conditions. Linking to the primary issue undergoing investigation, gastroscopy was recommended to evaluate the horse for gastric ulceration, which was one of the most consistent causes of girthiness found.
SO far, there are overlapping signs of pain and behaviour for kissing spines and EGUS, but what about lameness? The signs of lameness, beyond the obvious asymmetry of the gait, have been reported to include: bucking, rearing, gait too slow, intense stare, sclera exposed, eyes half/shut, lids closed [3 & 9]. Again, quite a lot of familiar signs of pain, and certainly not distinct from those reported for pain from other regions.
Further work has been carried out, back stepping from behaviours when ridden, to the behaviour observed during tacking up of the horses and when being mounted [10]. In Dr Dyson’s study as 193 riders were mounting, or immediately after, 26.4% (n = 51) of the horses fidgeted,17.1% (n = 33) swished their tail, 16.8% (n = 32/191) chomped on the bit, 14.0% (n = 27) extended the thoracolumbar region, 12.4% (n = 24) yanked down on the reins, 10.9%(n = 21) tossed their head and 7.8% (n = 15) needed to beheld. Some of the horses (<2.6%) were seen to flex the thoracolumbar region (n = 5), grind their teeth (n = 5), kickout with a hindlimb (n = 5), paw the ground with a forelimb(n = 3), attempt to bite (n = 2), or yawn (n = 1)
The analysis of the behaviours during tacking up were contrasted to the signs of pain also assessed for and there was a significant relationship between epaxial muscle pain, lameness and tight tree points. The authors suggest that such behaviour is in anticipation of pain, either caused directly by the tack or reflecting musculoskeletal pain during ridden exercise.
In conclusion, we need to be aware that behaviours displayed during tacking up, mounting and ridden work may be due to the anticipation of, or actual pain. When comparing diagnoses the behavioural signs of pain are common for different causes, there is an overlap in reported expressions of pain for back pain, for pain from equine gastric ulcer syndrome and for pain that causes lameness.
References
[1] Gleerup KB, Forkman B, Lindegaard C, Andersen PH. An equine pain face. Veterinary anaesthesia and analgesia. 2015 Jan 1;42(1):103-14.
[2] Dalla Costa E, Pascuzzo R, Leach MC, Dai F, Lebelt D, Vantini S, Minero M. Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier. PloS one. 2018 Aug 1;13(8):e0200339.
[3] Dyson S. The ridden horse pain ethogram. Equine Veterinary Education. 2022 Jul;34(7):372-80.
[4] Jeffcott LB. Disorders of the thoracolumbar spine of the horse—a survey of 443 cases. Equine Veterinary Journal. 1980 Oct;12(4):197-210.
[5] Coomer RP, McKane SA, Smith N, Vandeweerd JM. A controlled study evaluating a novel surgical treatment for kissing spines in standing sedated horses. Veterinary Surgery. 2012 Oct;41(7):890-7.
[6] Prisk AJ, García‐López JM. Long‐term prognosis for return to athletic function after interspinous ligament desmotomy for treatment of impinging and overriding dorsal spinous processes in horses: 71 cases (2012–2017). Veterinary Surgery. 2019 Oct;48(7):1278-86.
[7] de Souza TC, Crowe OM, Bowles D, Poore LA, Suthers JM. Minimally invasive cranial ostectomy for the treatment of impinging dorsal spinous processes in 102 standing horses. Veterinary Surgery. 2022 Jul;51:O60-8.
[8] Millares-Ramirez EM, Le Jeune SS. Girthiness: Retrospective study of 37 horses (2004–2016). Journal of Equine Veterinary Science. 2019 Aug 1;79:100-4.
[9] Dyson S, Berger J, Ellis AD, Mullard J. Development of an ethogram for a pain scoring system in ridden horses and its application to determine the presence of musculoskeletal pain. Journal of Veterinary Behavior. 2018 Jan 1;23:47-57.
[10] Dyson S, Bondi A, Routh J, Pollard D. An investigation into the relationship between equine behaviour when tacked‐up and mounted and epaxial muscle hypertonicity or pain, girth region hypersensitivity, saddle‐fit, rider position and balance, and lameness. Equine veterinary education. 2022 Jun;34(6):e258-67.
