In group resting areas, horses wake each other up and force each other to move about every 10 minutes. And when the space is too small, they end up only getting about half the amount of sleep they do when they have larger resting spaces, said Linda Kjellberg, a PhD candidate in the department of anatomy, physiology, and biochemistry at the Swedish University of Agricultural Sciences, in Uppsala.

“Group housing gives horses the opportunity to have freer movement, but also more opportunities to show their social behavior,” Kjellberg said. In group housing, that social behavior can cause disrupted sleep patterns. “Sleep is a welfare issue for a lot of horses, and we have to give them enough opportunity to sleep. It’s important to be sure we’re not impairing the total welfare, just to make some welfare issues better.”

Housing Affects Sleep

Group housing has become popular in Sweden and other parts of Europe, Kjellberg said. But until recently, researchers had not studied how this management style influences horses’ sleep.

So Kjellberg and her fellow researchers studied sleep habits in 12 Swedish Warmblood geldings, aged 3 to 17, at the Swedish National Equestrian Centre Strömsholm. The horses were used for riding classes and training three to four days per week. They ranged from 16.1 to 17.2 hands tall and had been housed in a group prior to the study.

The researchers placed the horses in four housing situations for 10 days:

• Box Stall: Single 114-square-foot box stalls at night and group paddock by day;
• Small Lying Area: Group paddock day and night with one shelter providing 86 square feet of lying space per horse;
• Medium Lying Area: Group paddock day and night with two shelters providing 194 square feet of lying space per horse; and
• Large Lying Area: Group paddock day and night with one shelter providing 300 square feet of lying space per horse.

In the box stalls the horses had wood shavings. In the shelters lying spaces were bedded with about 12 inches of straw.

Box Stalls and Medium-Sized Areas

In all the shelters, regardless of size, the horses disturbed each other and got up about every 10 minutes, Kjellberg said.

Enclosure size mattered when it came to the total amount of sleep horses got, including lying in sternal position on the chest and lying flat out on the side—which is when horses generally enter the most restful state of sleep (although horses can sometimes also enter this state in sternal position with their heads dropped to the floor), she said.

Horses had the least amount of sleep in the smallest group rest area in the study, said Kjellberg. On average, the horses laid down less often and for shorter periods–only 69 minutes per 24-hour period, compared to 145 minutes in stalls, which included 52 minutes of lying fully on their sides.

The average time lying on their sides in the small rest area was 22 minutes per 24 hours, she said. Three of the horses only spent half that much time lying on their sides—and one never laid down fully. That horse, she added, never lay down on his side in the individual box, either—suggesting he would be at risk of sleep deprivation if kept in a stall or a paddock with a small resting area.

By contrast, the horses in individual box stalls and medium lying areas got similar amounts of sleep—averaging 130 minutes per 24-hour period. The difference in lying time between the medium and large areas (132 minutes) was not significant, suggesting farm managers do not need to invest in excessively large resting areas.

Lying occurred in several bouts over the 24-period and varied according to the housing situation, Kjellberg added. Each horse would lie down one to six times in the stalls, two to six times in the medium rest area, and zero to five times in the small rest area, she said.

She said they noted no significant differences between individual horses. While free-roaming horses in the wild sleep in groups, Kjellberg said they can choose their groups—unlike domestic horses.

“All groups aren’t best buddies,” she said. “They might respect that they have to share their space, but that’s different from being best buddies. So they might need more space.”

Paddocks and Pastures

While horses might lie down on hard ground, they are more likely to sleep longer and more frequently when bedding is comfortable and they feel safe and secure, Kjellberg said.

“I don’t think just laying down outside in the paddock is always a safe and comfortable opportunity for horses,” she said. “Of course, if that’s all that is offered to them, they might lie down … In our study, there was one horse we saw lying down twice in the hard surface outside the bedded area during the (small rest area test), but we hadn’t seen him do that before or after. He needed to lie down, but it just wasn’t comfortable enough for him to squeeze in with the other horses.”

Horses’ resting behaviour in shelters of varying size compared with single boxes first appeared in Applied Animal Behaviour Science in 2022.