15/12/2022
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Pain Management in Horses
Brian S. Burks DVM
Diplomate, ABVP
Board-Certified in Equine Practice
The term pain comes from the Latin work peona, meaning a penalty. Horses experience acute and chronic pain; managing pain is critical to minimizing secondary problems. Pain is a part of life; indeed, it is necessary for life. Pain often produces a withdrawal response or avoidance behavior that is protective in nature- continuing the current behavior may result in permanent dysfunction or even death. As a medical professional, keeping in mind the above statement, striving to control pain is important, which often means correcting the underlying problem. If, say, a fracture heals, then the pain will cease. In the meantime, post-operative pain needs to be controlled.
Horses, like people, become injured and suffer pain in a variety of ways. Lacerations, punctures, fractures, burns, chemicals, etc. all cause pain. These result in emergencies daily. Pain can also come from injury during a disaster, such as a major storm.
The sensation of pain is initiated in the peripheral nerves, often in very small nociceptive c-fibers. Pain is transmitted from the site of injury to the central nervous system, where it is consciously noted. Pain can obviously be from very small aches to unrelenting, excruciating pain. Stimuli causing pain includes heat, cold, tearing, blunt force trauma, penetrating injuries, or chemicals/toxins.
Horses suffer a range of painful stimuli:
■ Minor cuts/scrapes, fly bites, osteochondrosis dissecans (OCD) lesions, minor medical procedures (e.g., endoscopic guided biopsy, castration, arthroscopy), and minor musculoskeletal injuries such as a soft-tissue strain or bowed tendon.
• Fractured bones
■ Corneal (eye) ulcer, joint infection, abdominal surgery, and fractures.
■ Peritonitis (inflammation of the abdominal lining), exertional rhabdomyolysis (tying-up), and laminitis/founder with rotation and sinking of the coffin bone.
In horses, facial pain expressions can manifest as:
• Low or asymmetric ears and outwardly rotated ears;
• Angled appearance of the eyes;
• Withdrawn and intense stare;
• Dilated nostrils; and
• Tension of certain facial muscles.
Horses with musculoskeletal pain may be reluctant to ambulate, hold up a limb, hold a limb(s) in an abnormal position, swing around a foot, and spend an increased amount of time recumbent. Those experiencing colic may paw at the ground, look or bite at the abdomen, frequently lie down and then rise, sweat profusely, roll, groan, or exhibit bruxism.
With chronic pain, such as laminitis or arthritis, horses may exhibit weight loss, partial to complete anorexia, and decreased response to external stimuli. Acute pain may manifest as restlessness, anxiousness, dilated pupils and glassy eyes, flared nostrils, muscle tremors, profuse sweating, and increased respiratory and heart rates.
For many years, equine veterinarians have relied largely on phenylbutazone and other non-steroidal anti-inflammatory drugs (NSAID) for pain control, with a few older narcotic medications. Topical applications of ice and soothing poultices were used but produced limited pain relief and undesirable side effects.
“Pain and suffering are clinically important conditions that can adversely affect an animal’s quality of life.” This statement from the American College of Veterinary Anesthesiologists helped promulgate research into the physiology of pain. The development of newer drugs and administration techniques has afforded us with better ways to control pain.
Our current armamentarium for fighting pain relies heavily on the following:
• Non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (Bute) and flunixin meglumine (Banamine) and firocoxib (Equioxx);
• Steroidal medication such as dexamethasone;
• Opioids such as butorphanol, morphine, hydromorphone, and tramadol; and
• Xylazine and other α2-adrenergic agents used for sedation, anesthesia, muscle relaxation, and analgesia.
• Acetaminophen (Tylenol) is newer to the equine world, but has shown some promise when combined with firocoxib;
• Lidocaine nerve blocks or continuous rate infusions.
These types of medications have been available for some time, and are effective for a vast array of acute and chronic conditions, including:
• Lameness and musculoskeletal disorders, predominantly osteoarthritis (OA) and laminitis;
• Colic;
• Lacerations and other injuries;
• Corneal ulcers and other ophthalmic conditions; and
• Reproductive emergencies such as dystocia (difficult birth), metritis (inflammation of the uterus), and mastitis (mammary gland inflammation).
If you have ever experienced substantial discomfort, you know that single medications are not always effective, many medications wear off quickly, and some only come in oral form (which takes longer to have an effect as the medication must be absorbed from the gastrointestinal tract before reaching the bloodstream). Alternative therapies to improve pain management in both human and equine patients have been investigated.
Recent advances in equine pain management include:
• A COX-2 inhibitor NSAID called firocoxib. It is designed to offer strong pain relief without the damaging gastrointestinal side effects of some other NSAIDs;
• A transdermal NSAID ointment—diclofenac sodium—for delivery to only the treated area; this method of administration can prevent the systemic levels of NSAID that cause side effects;
• A transdermal narcotic patch that provides significant analgesia without side effects;
• A new method of using ketamine, an older anesthetic, for pain relief by administering it as an intravenous drip for several days in burned horses;
• Continuous rate infusion of narcotics and other analgesic medications;
• New techniques and materials for administering epidural (spinal) pain relief for weeks at a time with a very low rate of complication;
• Extracorporeal shock wave therapy is providing long-term pain relief for several equine orthopedic injuries; and
• New injection techniques to provide relief for joint pain, such as IRAP and stem cells.
Other types of pain management include supportive/nursing care such as a quiet area, deep bedding, wound care, hydrotherapy, application of heat or cold, bandaging or splinting, and physical therapy. Further, extracorporeal shock wave therapy (ECSWT) and surgery- such as injury repair or a neurectomy where nerves are cut- are used to help control pain.
Consider pain in horses as three types:
• Type I pain is commonly associated with sudden tissue damage—for example, from a kick. This type of pain is usually sharp, localized, and of limited duration.
• Type II pain is more diffuse and longer lasting than Type 1. By protecting the injured limb until that tissue has healed, Type II pain has apparent survival value.
• The most long-term and damaging pain, Type III, can develop when Types I and II progress without relief. The patient experiencing Type III pain no longer needs specific tissue injury to experience discomfort. Normal nervous system mechanisms that balance the excitement and inhibition of nerve pathways for pain act spontaneously and without controls. At this stage, chronic pain is considered a state of disease rather than as a symptom of disease, and affected patients often deteriorate further.
The goal of effective pain management is the restoration of normal sensation and the return of the patient to normal function. It is exciting to see this goal receive increased recognition in equine practice.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
Your horse's health is always our top priority
