We’re getting the message now: Horses don’t like being separated from other horses. And as the research pours in, we’re finding more and more support for that idea. Case in point: British researchers have confirmed that horses tend to show more physiological signs of stress when they’re housed in individual stalls, whether they act like it or not.

“The physiological changes we saw in our study horses cannot be masked in the same way that a horse can mask behavior (a survival mechanism in a prey species),” said Kelly Yarnell, PhD, researcher at Nottingham Trent University, in Nottingham, U.K. “And unfortunately, in the most isolated housing (individual box stalls), adrenal activity was very high (which can result in high levels of cortisol, the “stress hormone,” being released). If very high levels of cortisol are present chronically or on a highly repetitive basis, then this can be detrimental for our horses’ health.”

In their study, Yarnell and her colleagues tested fecal cortisol levels, eye temperature, and behavior during handling in 16 university lesson horses housed in four environments:

  • Individual box stalls with no physical contact;
  • Individual box stalls with limited physical contact;
  • Group stalls housing two horses together; and
  • Group pens housing several horses together.

All horses were on a break from lessons during the summer and were kept in a pasture before the experiment began. They had, however, all been introduced and were accustomed to each kind of housing situation before the study began, so nothing was new.