Horses typically sleep more when they have deeper bedding—which might also affect their moods and, consequently, their well-being and physical and mental capacities, said Amber Matthews, MSc, equine lecturer at Hartpury University, in Gloucestershire, U.K.

“We are starting to see more how we can impact the amount of sleep a horse achieves from bedding practices,” she said during the 2022 International Society for Equitation Science (ISES) Conference, held Aug. 9-12 in Hartpury.

“This could mean that we could have a happier horse,” she said. “And that would, of course, increase equine welfare and potentially performance.”

Bedding Depth and REM Sleep

Researchers already know bedding depth matters when horses sleep, Matthews said. Bedding depth can affect the amount of rapid eye movement (REM) sleep horses experience, which requires the horse lying down on his side or, in some cases, on his chest with his nose on the ground. A lack of REM sleep can lead to horses falling into deep sleep while standing and literally collapsing. But researchers had yet to investigate the effects poor sleep has on horses’ moods.

Matthews and her fellow researchers tested six mixed-breed riding school horses, averaging 15 years old, housed on different depths of wood shavings. Half the horses started the experiment on 2-inch (5-centimeter) deep bedding for five nights, and the other half started with 6-inch (15-centimeters) deep bedding for five nights. Then, after a five-day period back on their standard bedding, all six horses switched to the opposite experimental bedding for five nights.

The team recorded each horse in their usual stable from 7 p.m. to 7 a.m. using infrared cameras. They assessed the amount of time the horses spent lying down completely, lying on the chest with or without the nose down, and sleeping standing up (non-REM sleep).

They found the horses spent significantly more time in REM sleep—as well as non-REM sleep—in the deeper bedding, Matthews said.

Sleep Quality Might Influence Optimism

Before this study commenced, the researchers trained the horses to find treats in a bucket in one part of an arena and nothing in a bucket in another part. They then placed a bucket between the two original locations and observed how likely the horses were to check the new bucket. This was the start of a cognitive bias test that measures animals’ optimism.

To determine how sleep influences optimism, the team tested the horses’ interest in the “in-between buckets” after each five-night stay in an experimental bedding thickness.

The horses that had a better night’s sleep tended to show more optimism in the cognitive bias test, Matthews said. Despite this tendency, though, the results in this small study did not reach a level of scientifically statistical significance, she added.

Take-Home Message

These findings support previous study results showing bedding depth impacts equine sleep, and they suggest a link between equine sleep and mood. Further research would provide greater clarity, Matthews said.

How that might affect training performance remains to be investigated, she explained. “It’s definitely of interest to think about that.”