Free-ranging horses are very social and live in large mixed-age herds. Even so, domestic horses are often individually stabled. Welfare concerns about social isolation, as well as evidence that turning horses out in pairs, small groups, or herds is beneficial,1 have led to changes in equine housing practices.

But what happens when the horse is removed from the herd? Separating a horse from its companions for veterinary care, hoof trimming, or training is likely more distressing for group living than for individually stabled horses. The distress might also be more severe when the procedure is painful or unpleasant.

In a recent study published in the Journal of Veterinary Behavior, Katherine Reid, MS (Biomed), BVSc, and associates at Massey University’s Equine Research Centre, in New Zealand, evaluated what happens when horses are isolated from conspecifics during routine equine management procedures.2 They looked at the separate and combined effects of social isolation and mild pain in six Standardbred horses which had lived together on pasture for two years as part of the university’s teaching herd and were regularly handled by veterinary staff and students.

To see how horses would respond behaviorally and physiologically to social isolation and mild pain, the researchers first placed each horse in a turnout next to a familiar herdmate, with visual, olfactory (scent), and tactile contact over a fence. After an acclimation period, they tested each horse in three challenging situations:

  • Social isolation (they removed the herdmate from the area);
  • Mild physical pain (in which they pinched the skin on the horse’s neck with clamp forceps for five minutes); and
  • Social isolation and mild pain combined.

In each situation, the researchers recorded changes in the horses’ behavior and physiology. They observed several behaviors that have been linked to anxiety and pain in previous research, including locomotion, restlessness, kicking with the hindleg toward the pain source, flexing the neck around toward the pain, grinding teeth, chewing, headshaking, pawing, tail swishing, urinating or defecating, and seeking contact with the human observer.

The researchers also recorded the horses’ heart rates and heart rate variabilities; periodic beat-to-beat variation is normal during resting conditions, but this heart rate variability decreases during stressful conditions.

One of the team’s key findings was that social isolation seemed to eclipse pain expression. When horses were socially isolated but did not experience pain, they were restless, moved around, vocalized, and sought human contact. In contrast, when horses experienced mild pain but had a familiar companion nearby, they moved around, sought human contact, and vocalized less often. When horses experienced both social isolation and mild pain, they were restless, but no more so than when they were only socially isolated; this means the isolation appeared to mask pain’s effects.

The researchers observed a similar pattern in the horses’ physiological measurements. Horses who were socially isolated, with or without mild pain, showed increased distress with higher heart rate and lower heart rate variability. In contrast, horses who experienced pain and had a companion nearby didn’t show any changes in heart rate.

“Social isolation is perceived by the horse as a greater threat than pain,” the authors noted in their study They cautioned that, as a result, caretakers might underestimate the amount of pain and administer insufficient analgesia to anxious horses and recommended taking anxiety into account when assessing pain levels.

This study shows that, for horses normally housed and/or turned out in social groups, having a familiar, calm companion nearby could help reduce anxiety during routine management procedures. Making use of an experienced companion is already a common practice in situations such as trailer loading, and one research study showed that young horses who had observed an experienced demonstrator horse were less anxious about crossing a novel surface.3 If recruiting a companion isn’t possible, an interesting but untested alternative might be to use a model or a phantom image, which has been shown to reduce the heart rate of mares separated from their foals.4

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