Veterinarians and owners can use a variety of methods to detect pain in horses
As you unlatch the paddock gate, expecting your horse to come running for breakfast, you notice him standing in the back of his run-in, head and neck lowered, with his right front leg extended ever so slightly. He raises his head at your entry but remains where he stands. Although hardly dramatic, this is not his usual behavior. If your horse had words, he’d shout, “Look!” He is, in fact, speaking loudly through his posture and facial expressions, conveying he’s in pain from an injury incurred overnight.
Horses can be demonstrative in how they communicate with humans—they nuzzle for affection, and they display certain body postures when resisting or acquiescing to an interaction or event. Somewhat unique among other species in the animal kingdom, they can make facial and eye expressions that convey volumes if you understand what you are seeing. In this article we’ll explore how you can use these expressions and body language to pick up on painful conditions your horse might be experiencing.
Behavioral Signs of Pain
During a visit to the doctor’s office, you might have seen a wall chart with multiple faces, exhibiting big smiles, deep frowns, tears, and everything between. Physicians use this Visual Analogue Scale (VAS) of 1 to 10 to score pain in people who can verbally communicate what they are feeling. Because we can’t rely on horses to tell us what they’re feeling, we use other observations to determine if a horse is in pain and, if so, how much.
Historically, the main implement in our equine pain detection toolbox has been behavior. A horse that acts out might do so for no reason or a reason unrelated to pain, such as social factors. Or his behavior might indicate true discomfort. Indicators that all is not right can include:
- Reduced weight-bearing on a painful limb;
- Flank-watching, pawing, rolling;
- Decreased activity;
- Diminishing interest in surroundings;
- Retiring to the back of the stall or paddock;
- Standing with head lowered;
- Decreased appetite;
- Decreased socialization;
- Self-mutilation, such as chewing on a painful leg;
- Change in attitude and/or performance;
- Rearing when ridden;
- Hypersensitivity of the flanks; and
Physiologic Signs of Pain
Other pain indicators include an elevated heart rate and increases in blood cortisol (the stress hormone) and/or β-endorphins (a natural pain suppressor). Elevated oxytocin (a social bonding and reproduction hormone) levels can also indicate reduced well-being.
Lea Lansade, PhD, and her colleagues at the French Horse and Riding Institute and the National Institute for Agricultural Research, in Tours, France, have been studying oxytocin in horses.
“A low level of basal (the minimal level that achieves a physiologic effect) oxytocin could be a marker of better well-being, in a social context,” she says. “For instance, higher basal levels of oxytocin in plasma were observed in prairie voles subjected to chronic social isolation, in lambs reared without a mother, and in humans with greater relational distress. It is also known that oxytocin affects levels of anxiety and stress, and during periods of distress oxytocin levels increase. This could also be the case in horses, but further research is required to confirm this result and understand the underlying mechanisms.”
Future studies on eye blink rate might also yield more information, because blink rate is associated with levels of dopamine, a neurotransmitter that tends to elevate with pain.
Testing for Pain
Owners and veterinarians can test horses for pain using a variety of methods. One is gauging a horse’s response to analgesics (painkillers) such as non-steroidal anti-inflammatory (NSAID) or opioid-type medications. They can also palpate or manipulate limb structures to see if the horse withdraws from the touch due to discomfort. A device called a pressure algometer allows them to detect areas of back pain by amplifying pressure over a suspected injury until the horse reacts.
However, all these methods are time-consuming and don’t always correlate with pain, because a variety of other stimuli might elicit similar behavioral changes or elevated heart rates.
This article continues in the December 2019 issue of The Horse: Your Guide to Equine Health Care. Subscribe now and get an immediate download of this issue, including this in-depth feature on a variety of methods veterinarians and owners can use to detect pain in horses.