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Understanding Pain in Horses
Merriam-Webster defines pain as “a localized or generalized unpleasant bodily sensation or complex of sensations that causes mild to severe physical discomfort and emotional distress and typically results from bodily disorder such as injury or disease.”
For those of us who have experienced real pain ourselves or witnessed a horse in pain, this definition might seem cold and distant … far from just unpleasant! It simply fails to adequately describe the excruciating nature of pain or the emotional toll it takes on its victims.
Further, this definition doesn’t address the different types of pain horses can experience.
NOCICEPTIVE PAIN
The traditional acute pain many of us think of is called nociceptive pain. This occurs when a noxious stimulus, such as extreme heat or cold, tearing, crushing, penetrating injuries, chemicals/toxins, and inflammation, triggers pain receptors in one part of the body. More specifically, horses can experience nociceptive pain after fracturing a bone; sustaining a penetrating injury or laceration or a tendon or ligament tear; or developing acute laminitis—inflammation in the sensitive layers of the hoof.
These stimulated pain receptors at the site of injury or inflammation in turn activate local (peripheral) sensory nerve fibers. Those sensory nerves start a signal, called an action potential, and transmit it to the spinal cord, then the brain. Different areas of the brain then perceive the details of the pain—where exactly the pain is located and how intense it is.
Some of the pain fibers can transmit the pain signal so quickly that animals withdraw from the painful stimulus before they even register how painful it was (e.g., touching an electric fence with their nose and reflexively leaping backward).
NEUROPATHIC PAIN
In this type of pain, damaged or dysfunctional nerves send abnormal signals to the brain, resulting in the horse perceiving pain.
INFLAMMATORY PAIN
Inflammation also causes pain. One mechanism of inflammatory pain involves the stimulation of pain receptors by the inflammatory mediator tumor necrosis factor alpha (TNF-α). Veterinarians need to identify and treat nociceptive, neuropathic, and inflammatory pain, preferably using a multimodal treatment approach, because “one-stop shopping” in the pain treatment aisle does not exist. They select from a variety of pain medications based on the perceived pain level, such as:
- Non-steroidal anti-inflammatory drugs (NSAIDs, e.g., phenylbutazone [Bute] or flunixin meglumine [Banamine]);
- Steroids (e.g., dexamethasone);
- Opiates/narcotics (e.g., morphine, hydromorphone, butorphanol);
- Alpha-2 agonists (α2, g., xylazine);
- Dissociative anesthetics (e.g., ketamine); and
- Local anesthetics such as lidocaine or bupivacaine.
Dr. Garfinkel can administer these drugs by several systemic routes such as intravenously (IV), intramuscularly (IM), or subcutaneously (SC/SQ); intra-articularly (IA, into a joint); orally (per os, PO); via epidural injection (into the spinal canal but not the spinal cord itself); via regional perfusions; and topically/transdermally (through the skin).
“With improvements in management and veterinary care, we are seeing horses live longer lives and remain in work for more years than ever before. With these changes, the incidence of chronic pain is inevitably going to increase, making it essential that we find more effective ways of mitigating and managing pain in affected individuals. The need for long-term therapy makes it imperative that we identify therapeutic approaches to pain management that do not carry high levels of risk for complications. The multimodal approach is one of the key ways in which we can make progress in achieving this goal.
If you think your horse is in pain call us at 619-659-1180.
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