3 Sept 2018
April Lawson and Stefania Scarabelli look at dealing with types of discomfort in horses, possible problems, latest ideas and numerous treatment options.
Pain management is of great importance when considering equine welfare. The recognition of pain is a necessity to enable appropriate management. Pain scales for horses have increasingly been published, and are likely to demonstrate utility and benefit in equine practice.
Managing pain for different clinical conditions involves a varied approach, and a multitude of methods, complications and research have been explored in the management of visceral, orthopaedic, laminitic and perioperative pain. Inherent concerns exist in masking certain types of pain, especially colic, and these will be discussed in this article.
Multimodal analgesic approaches – with drugs acting at different levels of the pain pathway – play a crucial role in the management of different types of pain.
This article will explore some of the medications, techniques, and their benefits and complications, as well as ancillary therapies – such as acupuncture, physical manipulation with ice and heat, magnetic field compression and movement – that have been described as part of pain management and rehabilitation plans in the horse.
Appropriate pain management in horses requires the ability to recognise and measure pain. In animals, this is no easy task.
Many scales have been developed in an attempt to quantify pain, such as:
Equine-specific pain scales are also being investigated (de Grauw and van Loon, 2016; Gleerup and Lindegaard, 2016).
Horses in the EU are considered by law to be food-producing animals and certain pain medications may preclude horses from entering the human food chain. This should be declared in their passport.
Information about legislation can be found at www.vmd.defra.gov.uk
Challenges associated with treating the acute trauma patient include excitement, distress, pain and significant blood loss. Case-dependent considerations may include cardiovascular, respiratory and intracranial pressure status. A chemical restraint is often required in the first instance, and alpha-2 agonists will provide sedation and analgesia; however, these can have deleterious effects on the cardiovascular system, particularly at the higher doses often required in excited animals. The adjunct of an opioid can be helpful to decrease the dose of the alpha-2 agonist.
Acepromazine is less reliable than an alpha-2 agonist, is not an analgesic and should be administered with caution in hypovolaemic or excited animals.
In head trauma cases with suspected increased intracranial pressure, opioids should be administered with caution since hypoventilation can worsen this condition. Additionally, if sedated, care should be taken to not allow the horse’s head to drop below the level of the heart.
NSAIDs have anti-inflammatory and analgesic properties, but hypovolaemia – a possible complication in acute trauma – can increase the risk of nephrotoxicity.
In both the hospital setting and the field, multimodal analgesia should be performed when a surgical procedure is undertaken. The type and intensity of surgical stimulus influences drug choice. When possible, local anaesthesia should be performed as an effective way to provide analgesia by interrupting transmission of the painful stimulus. Description of loco-regional techniques is beyond the scope of this article; the reader can refer to Michou and Leece (2012).
It is the authors’ belief all horses should receive an NSAID prior to surgery unless a significant contraindication exists. No scientific evidence has demonstrated one NSAID is a “better” analgesic than another for specific situations and, most commonly, the choice is dictated by the clinician’s preference or ease of administration. NSAIDs can be continued as required at the recommended dose postoperatively.
Opioids are commonly administered during surgical procedures. Butorphanol, buprenorphine and pethidine are licensed opioids in horses, and butorphanol is commonly used in equine practice. In the authors’ practices, morphine is the most commonly used opioid for surgical procedures – usually at a dose of 0.1mg/kg to 0.2mg/kg. Morphine is best administered after (for example, an alpha-2 agonist) sedation to prevent excitation in non-painful animals.
Some quarters have been reluctant to administer full mu-agonists, such as morphine, due to the perceived adverse effects on gastrointestinal motility and locomotor excitement. In practice, the limited adverse effects of administration are rarely seen, and are outweighed by the analgesic benefits. It is also worth considering pain itself will cause a significant reduction in gastrointestinal motility.
Continuous rate infusions (CRIs) during anaesthesia of some analgesic agents may provide analgesia and decrease the minimum alveolar concentration of inhalant anaesthetics. However, these agents can have deleterious side effects – for example, lidocaine can worsen recovery by inducing ataxia, so infusion should be stopped 30 minutes before recovery; alpha-2 agonists cause decreased cardiac output and peripheral vasoconstriction; and ketamine can cause recovery problems (Gozalo-Marcilla et al, 2014; 2015).
Visceral pain may originate from ischaemia, distension of organs or organ capsules, traction of the mesentery, and inflammation. It should be, therefore, controlled for the welfare of – and to minimise risk of injury to – horses and handlers. Appropriate pain control has significant benefits on recovery of horses following colic (Mair, 2017):
Following major surgery, the predominant causes for postoperative ileus are pain, inflammation and stress. Pain scoring is warranted and the authors advocate the use of composite pain scales in this context.
Common clinical issues with chronic orthopaedic pain include welfare, side effects due to long-term NSAID management, and governing body medication restrictions with certain medications. An increasing number of treatment options are available, especially for the management of chronic orthopaedic pain, including systemic treatment, targeted treatment (for example, intra-articular medication), adjunct therapy and surgical management.
Systemic treatment often involves NSAIDs for pain management. Long-term NSAIDs may be useful in non-competing horses, with anecdotal evidence indicating phenylbutazone is “most” effective for orthopaedic pain.
Care must be taken over prolonged administration. Possible complications, such as colitis and renal toxicity, should be monitored and warned for. Selective cyclooxygenase-2 inhibitors have become of interest for their potential reduction in adverse effects, although evidence is lacking (Doucet et al, 2008). Other drugs, such as bisphosphonates, may be appropriate for modifying disease processes.
Targeted treatments – for example, intra-articular medications – may be deemed more effective with fewer side effects than drugs administered systemically. Several treatment options are available, including corticosteroids, hyaluronic acid, polyacrylamide hydrogel, as well as regenerative medicine products (autologous conditioned serum or interleukin-1 receptor antagonist protein), platelet-rich plasma and stem cells, to mention a few (McIlwraith, 2015).
Corticosteroids are the most widely used and regarded as the most effective, among which triamcinolone acetonide is suggested to be the more chondroprotective. Corticosteroids may be contraindicated or administered at lower doses in horses at high risk of laminitis.
Adjunct therapy may encompass rest, physiotherapy and rehabilitation. Primarily, many injuries require appropriate rest and rehabilitation periods, whereas more advanced injuries may necessitate surgery. Rehabilitation may include the treadmill, farriery and shockwave (Yocom and Bass, 2017); specific adjunct therapy will be dependent on condition (Figure 2).
Surgical management may be required in circumstances of advanced injuries, and these procedures may encompass arthroscopic treatments, arthrodesis (for example, of the proximal interphalangeal joint), neurectomy (such as of the palmar digital nerve or deep branch of the lateral plantar nerve) and ostectomy/ desmotomy (for example, for the impingement of dorsal spinous processes). Salvage surgeries, fundamentally, require appropriate case selection and complications may occur.
Uncontrolled pain is undoubtedly one of the main characteristics of horses suffering from laminitis. Depending on the stage and cause of the disease, different types of pain can be involved – from inflammatory pain in acute stages, to neuropathic pain in chronic cases. The involvement of different pain pathways underlies the importance of a multimodal analgesic approach.
Several drugs have been used to provide pain relief in the laminitic horse:
Other strategies:
Acupuncture has been part of traditional Chinese veterinary medicine for centuries and, nowadays, is integrated into the health care of animal patients. It can contribute to the rehabilitation of competition horses and be used to help relieve pain in many musculoskeletal disorders, and promote tissue healing and muscle strength (le Jeune et al, 2016).
Two types of magnet therapy are available – static and pulsatile. Static implies the use of iron, steel or other elements that generate a constant magnetic field. Pulsatile requires electricity to generate a pulsed magnetic field. Pulsed electromagnetic fields (PEMF) provides analgesia mainly through an opioid-mediated effect and changes in blood flow to the affected area, and are used in human medicine to treat chronic and neuropathic pain. PEMF has been anecdotally used in horses to treat several conditions, including arthritis and laminitis, but, to the authors’ knowledge, no scientific reports exist evaluating its efficacy.
Veterinary manual therapy includes a variety of manipulative techniques, such as massage, chiropractic and osteopathy. Evidence exists for its effectiveness in human patients suffering low back pain, but evidence is limited to support the effectiveness of spinal mobilisation and manipulation in reducing pain in horses.
The authors would like to thank Mark Senior for reviewing the article, and Peter Milner and David Stack for appraising the chronic orthopaedic pain management section.
