Understanding Equine Pain

Would you know if your horse was in pain? "Sure," you think, perhaps picturing your horse with a notable limp or a gaping wound. But what about less dramatic scenarios? Does it hurt your horse when you pull his mane, give him an injection, or have him freeze branded? Would you know if he had internal discomfort or a low-level, nagging ache? What signs would you look for?

The reality is that identifying pain, not only in the horse world but in the animal kingdom at large, challenges even the professionals, from veterinarians to behaviorists. Through diligent observation and scientific research, our understanding continues to grow, improving our ability to assess pain in animals and manage it, so we can better give our horses the optimal quality of life they so richly deserve.

The Challenge of Individuality

What makes pain so difficult to assess and quantify? To begin with, regardless of species, there are differences in pain perception, says Bonnie Beaver, DVM, MS, Dipl. ACVB, a behaviorist at Texas A&M University. "If you rate pain on a scale of zero to 10, what's a seven for me might be a two for someone else," she explains.

Beaver, along with a veterinary student, a surgeon, and an anesthesiologist, conducted a study on ways to evaluate pain in horses. In part, the study looked for behaviors that would consistently indicate pain. "On an individual level, we could make that determination, but not across all horses," she notes.

The degree to which a horse expresses pain also varies from individual to individual, says Sue McDonnell, PhD, a Certified Applied Animal Behaviorist and head of the Equine Behavior Lab of the Veterinary School of the University of Pennsylvania. She sees many equine patients each year with behavioral problems stemming from pain-related sources. "Some horses don't show pain, and with some, it's right on the surface," she says. "It's great to have that stoicism for training--the horse just takes things in stride. But when they're hurting, it's harder to know, and we often don't recognize the pain soon enough."

Individual pain tolerances and/or reactions to pain might also vary based on such factors as the horse's age, sex, previous experiences, and even familiarity with the given environment or circumstances, says Sukumarannair S. Anil, BVSc, MVSc, PhD. A researcher in the University of Minnesota's Department of Veterinary Population Medicine department, Anil and colleagues Leena Anil, BVSc, MVSc, PhD; and John Deen, DVM, PhD, Dipl. ABVP, published a paper discussing types of pain in animals and the difficulties in identifying pain. "Pain threshold has been reported to vary during estrus, in late pregnancy, and immediately after birth," says Anil. "Position within a social hierarchy, ability to learn adaptive behaviors, and concurrent stressors all can cause variation in the animal's response to a pain stimulus."

Looking for Universal Indicators

Considering these challenges, it's no wonder that, as Anil says, there is no universal, objective tool for accurate pain assessment in animals. Traditional diagnostic tools, such as radiographs, ultrasounds, and nuclear scintigraphy, can help your veterinarian pinpoint an underlying cause of pain. But they can't actually tell you whether your horse is in pain or how much pain he is feeling. Research on these topics, however, is ongoing.

For instance, Anil notes that researchers at the University of Edinburgh have produced a behavior-based model, in a clinical setting, for studying pain in horses and the efficacy of analgesia (painkilling). He adds, "Pain scoring systems developed to assess pain in human infants have been tried in animals, with modifications." Researchers have also attempted to assign specific behaviors to a pain-level scale, based on studying animals' behavior after routine surgical procedures. "However, these hypotheses are species- and injury-specific, and therefore cannot be generalized," notes Anil.

Physiological variables, such as cortisol levels, have also been reviewed as potential pain indicators. "For instance, studies in lambs have revealed that during painful conditions, such as castration, plasma cortisol concentration increases significantly with respect to that of control animals," says Anil. "However, no specific value has been suggested as indicative of pain, and these indicators are more helpful in detecting acute pain rather than chronic pain."

Also under scrutiny are endogenous opioids (i.e., endorphins and enkephalins); metabolic changes such as fluid and electrolyte imbalance, metabolic acidosis, or glucose or lactate imbalance; and EEG (electroencephalograph) and brain-mapping analysis, says Anil.

Your Inside Advantage

So if qualifying and quantifying pain challenges the professionals, how can you hope to pinpoint it for yourself? Knowing your horse and his normal behavior gives you an advantage. As Anil says, "The absence of normal behavior is the most striking sign of pain in animals." Thus, adds McDonnell, any abnormal posture, movement, expression, attitude, or behavior is a potential sign of pain.

This can include obvious signs such as lameness or vital signs outside the normal range. Or abnormalities might be more subtle, such as isolation from herd mates, changes in attitude, altered performance ability, loss of libido in breeding stallions, or increased vocalization.

The catch, of course, is that nearly all of these signs could also have nothing at all to do with pain, professionals agree. For instance, adds Anil, non-painful stimuli such as sighting a predator, eating, exercise, or environmental changes can all lead to behavioral modifications as well.

"The presence of more than one indicator of pain helps to confirm pain," he says.

Repetition or continuation of a specific unusual behavior can also help determine whether that behavior is linked to pain. To pinpoint these trends and patterns, McDonnell often videotapes the horse (left to its own devices) over a six- to 10-hour span. This way, an action that might seem insignificant while you're with the horse--such as shifting hindlimb weight--might show up as a recurring habit over the extended time period.

Noticing that your horse is in pain is only the first step, of course. Next, you must determine what's causing the pain and realize the catalyst might not be a single overriding problem, but a number of smaller issues, says McDonnell. For help in identifying the cause or causes, Beaver encourages you to seek veterinary assistance. After all, your regular vet will not only be trained to recognize signs of pain, but will also be familiar with your horse's usual habits and health, making it easier to spot abnormalities.

Can Pain Be Beneficial?

With the difficulties of identifying pain and pain levels, it's fair to ask how veterinarians know when to treat a horse for pain and how much treatment is necessary to attain a reasonable comfort level for the horse. McDonnell and Beaver agree that the trend is to err on the side of pain management. In other words, if it's not clear whether a horse is in pain, most vets now act on the assumption that the horse is hurting.

The reason is fairly simple, says Beaver: "Ideally, we don't want the horse to feel pain any more than we want to feel pain."

Adds McDonnell, "If an animal is in trouble or injured, people generally feel responsible to relieve that pain and suffering. And for human-animal relationships, the less pain we inflict, the better the relationship will be."

There are, however, some caveats to pain control. For one, says Beaver, there are a limited number of pain-relieving drugs available for horses, and all come with side effects. For instance, she says, "A little Bute is okay, but how much can you give before you get stomach problems?"

Plus, says Anil, it's important to realize that certain analgesics can mask clinical signs of the underlying cause of pain. This can interfere with accurate diagnosis, potentially affecting important decisions such as whether or not a colic case is severe enough to warrant surgery.

What's more, agree McDonnell and Anil, pain can even be beneficial. "It causes the animal to rest and guard itself, so it can repair," explains McDonnell. "It's nature's way of slowing down the animal and limiting his activity."

Adds Anil, "Indiscriminate elimination of pain may become counterproductive if that leads to permanent damage. Analgesics may not be enough to treat the condition, and by alleviating the symptoms, these drugs may encourage the horse to move more than it should in cases such as laminitis, thus causing further damage."

On the other hand, he continues, pain itself can adversely affect the animal, leading to additional troubles. For instance, a horse that won't eat because of pain is probably in greater danger if you don't treat the discomfort than if you do. Unfortunately, says Anil, there is no objective technique to tell you or your veterinarian where the cutoff point is between "enough" pain to limit potential damage and so much pain that it's likely to be counterproductive to the overall healing process.

But perhaps it isn't necessary to identify such a particular threshold. After all, says Anil, "We have the moral obligation to avoid suffering of animals. Therefore, it may be appropriate to give the animals the benefit of the doubt and, when you think the animal is in pain, supply analgesia."

Then, if you're concerned about the horse over-exerting himself because he doesn't feel the pain, you need to take the responsibility to be conscientious in your schooling and management of the horse's activities, says Beaver. For instance, you might temporarily place a pastured horse in a small pen or stall to limit motion and/or cut back on the horse's grain intake to reduce his energy levels.

While we've come a long way in understanding and treating pain in horses, there are obviously many questions still to be answered. And, as Beaver notes, research continues along these lines so that every year, we become a little more adept at knowing when our horses are hurting and how to more effectively bring them relief.


HOW DOES IT HURT? The Many Types of Pain

Just as in humans, horses can experience different kinds of discomfort. Sukumarannair S. Anil, BVSc, MVSc, PhD, a researcher in the University of Minnesota's Department of Veterinary Population Medicine department, published a paper along with his colleagues Leena Anil, BVSc, MVSc, PhD, and John Deen, DVM, PhD, Dipl. ABVP, that categorized animal pain in several ways:

By Depth

  • Superficial pain results from stimulation of pain receptors in the skin. Example: A minor flesh wound.
  • Deep pain occurs in underlying structures, such as muscles, joints, tendons, and ligaments. Example: A bowed tendon.
  • Visceral pain comes from stretch receptors in the walls of the internal organs (visceral walls), which are sensitive to changes in shape and tension. Example: Colic.

By Time Frame

  • Acute pain lasts only through the healing process of an injury. It's generally accompanied by autonomic changes (such as increased heart rate or blood pressure) and responds to analgesic treatment. Acute recurrent pain is prolonged pain that has a definite cause and is characterized by repeated attacks of acute pain. Example: A cut, a strained ligament, or colic.
  • Chronic pain has no obvious cause or time of onset. Definitions vary, but pain might be considered chronic if it lasts more than six months, persists after you would expect the original disease or injury to have healed, or involves an alteration of the nervous system so that the state of discomfort continues even if the initial cause is gone. Thus, chronic pain might not respond to treatments directed at the original cause of pain. It can also be more difficult to recognize because the animal becomes more tolerant of the pain and adjusts its behavioral patterns accordingly to minimize the pain. Example: Mild arthritis, a cracked tooth, or chronic laminitis.

By Clarity of Expression

  • Level One defines an animal that clearly expresses signs of pain. The pain is typically acute and of a high degree. Example: A horse with a broken leg or with severe, advanced colic.
  • Level Two horses do not express their discomfort through obvious abnormalities in posture or behavior due to a lack of ability or a lack of opportunity. Example: A horse might not show signs of lameness if he doesn't have the chance to walk at least a short distance. Likewise, if pain is associated with an occasional activity, such as urination, you might not notice it unless the horse is under constant observation or you're lucky enough to be watching at just the right time.
  • Level Three defines a situation where the horse owner or other observer believes the animal is in pain, but cannot prove it. Example: You might suspect that a horse is experiencing discomfort if he is suddenly unwilling to take the left lead or begins tossing his head when being bridled.--Sushil Dulai Wenholz

MANE PULLING, SHOTS, ETC.: So...Does it Hurt?

Given the challenges of determining whether or not an individual horse even feels pain, it's difficult to generalize about what actually causes pain in the first place. Some things we can all agree on: A pulled muscle, a broken bone, or a gaping wound hurt. But other scenarios aren't so easy. For instance, does it hurt your horse when you pull his mane or give him an injection? Watch his reaction to decide for yourself, says Bonnie Beaver, DVM, MS, Dipl. ACVB, a behaviorist at Texas A&M University.

"Mane pulling, for instance, yields individual reaction," she says. "Some horses could care less, while others wiggle and squirm all over the place." And use common sense, she adds. "If you had dry ice on your skin would it hurt? Yes. So is freeze branding painful? Probably." But, she adds, you have to weigh the benefits of the action against the discomfort it causes. Take vaccinations, for example, where the benefit of avoiding disease typically far outweighs the minor and temporary pain inflicted by the needle.

Bear in mind, too, that the horse's reaction to a potentially painful stimulus can be dependent on the novelty of the experience, says Sue McDonnell, PhD, a Certified Applied Animal Behaviorist and head of the Equine Behavior Lab of the University of Pennsylvania Veterinary School. A horse might become accustomed to having its mane pulled and learn to stand still as he learns the discomfort is mild and not prolonged. In addition, she says, "A lot of the horse's reaction is dependent on our reaction," particularly for potentially uncomfortable, but relatively necessary aspects of good horsekeeping, such as giving those injections, floating teeth, or dressing a wound. "If you make a procedure as painless as possible, then proceed as if this is just ordinary, most horses will tolerate it," she states.--Sushil Dulai Wenholz

About the Author

Sushil Dulai Wenholz

Sushil Dulai Wenholz is a free-lance writer based in Lakewood, Colo. Her work appears in a number of leading equine publications, and she has earned awards from the American Horse Publications and the Western Fairs Association.

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