The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". Pain is an important symptom in many medical conditions and can interfere with a horse’s general functioning, performance and quality of life. It is one of the main reasons for horse owners to consult their equine veterinarian but it can be difficult to objectively assess pain, particularly in our non-verbal veterinary patients.
Veterinarians and horse owners are often confronted with painful conditions in horses, varying from lameness to abdominal pain, post-surgical pain or more chronic pain states. Depending on the origin and intensity of pain, effective pain management can be provided either by single medications or with multi-modal analgesia. Dechra offers a comprehensive equine pain management range, helping vets and horse owners to confidently manage each equine patient.
What is essential for effective treatment of pain in horses?
Effective treatment of pain in horses relies upon:
- A good understanding of the underlying mechanisms of pain and the different steps in the pain pathway
- Effective recognition and monitoring of pain in the equine patient
- Availability of effective analgesic drugs, preferentially approved for use in horses
Pain and the pain pathway
What types of pain are commonly seen in horses? add
There are many different types of pain which can be classified according to origin, location, duration, etc. The types of pain most commonly encountered by equine veterinarians include:
- Lameness (common causes include pain in the foot, limbs and other parts of the musculoskeletal system, eg. the back and neck)
- Abdominal pain (colic)
- Post-surgical pain
- Painful conditions of the eyes or teeth
- Painful skin conditions or wounds
Pain Pathway Processes
The signal travels to the brainstem and to the cerebral cortex and higher brain centres where pain is perceived. Until the pain signal reaches the cerebral cortex pain is not perceived. However, even in the anaesthetised animal when pain may not be perceived, the sub-cerebral nociceptive mechanisms continue. This is why reflex responses such as increases in blood pressure may still occur in anaesthetised animals in response to surgical stimulus and why providing effective analgesia (systemically or via regional anaesthesia techniques) is vital even in the anaesthetised patient.
Molecules that target perception:
How to recognise pain in the horse?
What is important to consider when assessing pain in horses? add
When assessing pain it is important to remember what is normal behaviour for the horse/donkey and to recognise that observing the horse in unfamiliar surroundings (such as the hospital setting) or whilst under the influence of sedative medications can affect pain evaluation. Observing from a distance or via video recording can be helpful in some circumstances. Horses in pain can display certain general pain behaviours and can also display pain-specific behaviours and potentially changes in physiological parameters. Examples of pain-specific behaviours include decreased weight bearing due to orthopaedic pain and pawing, flank-watching and rolling in relation to colic pain. General pain behaviours include; restlessness, depression, decreased activity, decreased appetite and reduced interest in socialisation. Whenever a horse displays a dramatic change in attitude or performance it could be that pain is the underlying cause.
Various physiological parameters have been historically believed to correlate with degree of pain in the horse however studies have shown that this correlation is variable depending on the type of pain in most cases. Non-invasive blood pressure monitoring, serum cortisol and serum endorphins have been shown to correlate with pain but are practically less useful in the clinical setting.
How can EPWA (Equine Pain and Welfare app) help you monitoring pain in your equine patients?
Reliable pain recognition and monitoring are key for optimal pain treatment. EPWA has been developed by researchers from the Faculty of Veterinary Medicine at Utrecht University, in collaboration with De Paardenkamp Foundation and Friends of VetMed. EPWA aims to facilitate the recognition and monitoring of pain with the aim to improve welfare in equids. It provides a simple, accessible tool for clinicians, nurses and horse/donkey owners to be able to objectively measure a horse or donkey’s pain by means of Composite Pain Scale or Facial Expressions.
Dechra proudly supports EPWA.
How to treat pain in the horse?
Equine Pain Ladder
Local anaesthetics add
Local anaesthetics block the intracellular sodium channels and thus the development and transmission of an action potential, which leads to anesthesia in sensory fibres. Local anesthetics can be used for local and regional nerve blocks for diagnostic purposes (lameness examinations for instance) or for creating surgical conditions in sedated or anesthetised animals.
Courtesy Dr. Thijs van Loon, modification of the WHO Pain Ladder for Humans.
How does the anaesthetic protocol chosen affect intra and post- operative pain? add
We know that horses can react to nociceptive stimuli, even when anaesthetised. We also know that inadequate pain relief has been shown to adversely affect outcomes in terms of morbidity, mortality, complication rate, length of hospitalisation and overall cost of treatment in other species and this is likely to be the same for the horse. Not managing pain adequately is likely to adversely affect the nervous system, potentially causing hyperalgesia and allodynia.
Vets should be aware which drugs used in the anaesthetic protocol have analgesic properties eg. alpha-2 agonists, NSAIDs, opioids and ketamine, and which have no analgesic properties eg. acepromazine, midazolam, diazepam, isoflurane. This will allow proper planning of analgesia including preemptive analgesia, administered prior to surgery, and will ensure intra- and post-operative analgesia are provided. Good peri-operative analgesia is likely to smooth maintenance and recovery periods as well as improving overall outcomes.
Regional anaesthetic techniques allow more procedures to be performed during sedated, standing surgery, avoiding the risks associated with general anaesthesia. They also lower the requirement for general anaesthetics when used concurrently during general anaesthesia, improving analgesic efficacy and reducing the incidence of side effects from general anaesthetics.
Summary of key points
- Local anaesthetics: mepivacaine (Intra-Epicaine)
- Opioids: butorphanol (Alvegesic/Morphasol/Torphadine), buprenorphine (Buprenodale or Bupredine)
- NSAIDs: phenylbutazone (Equipalazone), meloxicam (Meloxidolor or Novaquin), ketoprofen (Ketodolor)
- NMDA receptor antagonists: ketamine (Anesketin)
- Alpha-2 agonists: detomidine (Domidine), romifidine, (Rominervin), xylazine (Nerfasin)
Bisgaard,T; Kehlet. H. and Rosenberg, J. (2001) ‘Pain and convalescence after laproscopic cholecystectomy’ Eur. J. Surg. 167; pp. 84-96
Bussieres, G; Jacques, C; Lainey, O; Beauchamp, G; Leblond, A; Cadore, J.L; Desmaiziéres, L.M; Cuveilliez, S.G. and Troncy, E. (2008) ‘Development of a composite orthopaedic pain scale in horses’ Res. Vet. Sci. 85; pp. 294-306
Dalla Costa, E; Minero, M; Lebelt, D; Stucke, D; Canali, E. and Leach, M.C. (2014) ‘Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration’ PLoS One 19:9; pp. 3
Dalla Costa, E; Stucke, D; Dai, F; Minero, M; Leach, MC. and Lebelt, D. (2016) ‘Using the Horse Grimace Scale (HGS) to Assess Pain Associated with Acute Laminitis in Horses (Equus caballus)’ Animals 6(8)
Gleerup, K,B; Forkman, B; Lindegaard, C. and Andersen, P.H. (2015) ‘An equine pain face’ Vet Anaesth Analg. 42(1); pp. 103-14
Graubner, C; Gerber, V; Doherr, M. and Spadavecchia, C. (2011) ‘Clinical application and reliability of a post abdominal surgery pain assessment scale (PASPAS) in horses’ Vet. J. 188(2); pp. 178-183
Sellon, D.C; Roberts, M.C; Bilkslager, A.T; Ulibarri, C. and Papich. (2004) ‘Effects of continuous rate infusion of butorphanol on physiologic and outcome variables in horses after celiotomy’ J. Vet. Int. Med. 18; pp. 555-563
Taffarel, M.O; Luna, S.P; de Oliveira, F.A; Cardoso, G.S; Alonso, J. M; Pantoja, J.C; Brondani, J.T; Love, E; Taylor, P; White, K and Murrell, J.C. (2015) ‘Refinement and partial validation of the UNESP-Botucatu multidimensional composite pain scale for assessing postoperative pain in horses.’ BMC Vet. Res. 11; pp. 83
van Loon, JPAM. and Van Dierendonck, M.C. (2019) ‘Pain assessment in horses after orthopaedic surgery and with orthopaedic trauma’ Vet. J. 246; pp. 85-91
van Loon, J,P. and Van Dierendonck, M.C. (2017) ‘Monitoring equine head-related pain with the Equine Utrecht University scale for facial assessment of pain (EQUUS-FAP)’ Vet. J. 220; pp. 88-90
van Loon, J.P. and Van Dierendonck, M.C. (2015) ‘Monitoring acute equine visceral pain with the Equine Utrecht University Scale for Composite Pain Assessment (EQUUS-COMPASS) and the Equine Utrecht University Scale for Facial Assessment of Pain (EQUUS-FAP): A scale-construction study’ Vet. J. 206(3); pp. 356-364
van Loon, J.P; Jonckheer-Sheehy, V.S; Back, W; van Weeren, P.R. and Hellebrekers L.J. (2014) ‘Monitoring equine visceral pain with a composite pain scale score and correlation with survival after emergency gastrointestinal surgery’ Vet. J. 200(1); pp. 109-115