Why REM Sleep Is Essential for Your Horse’s Health

Have you ever been very irritable because you slept badly or not at all? Has that ever made you wonder whether your horse experiences being tired just the same? What actually is a “good night’s sleep” for your equine partner?

Horses can only achieve REM sleep when they're able to lie down.

My horses recently moved boarding facilities, and my older horse, who has had a difficult time adjusting to living in the Netherlands, has finally found her place. But how can I tell?

One of the biggest indicators of her welfare improving is the time she now spends lying down and entering REM phases. According to research, both feral and domestic horses spend approximately 43-216 minutes per day lying down. Lying down is essential for REM sleep, because horses cannot achieve REM without it.

And that matters more than many owners realise.

(Kelemen et al., 2021)

But what is REM sleep?

REM sleep, rapid eye movement sleep, is the deepest sleep phase. During REM, muscle tone disappears almost completely. The body softens, the horse is fully supported by the ground, and the nervous system becomes highly active in processing and regulating.

This is why lying down matters so much. REM sleep is when the horse is truly able to relax and reset.

If you see your horse lying fully on their side, or resting on their belly with the head supported on the ground, they are most likely able to enter REM sleep. That position requires trust in the environment and comfort in the body.

Standing rest is not the same.

What happens if horses don’t get enough REM sleep?

In humans, reduced REM sleep is linked to impaired learning ability, reduced concentration, increased pain perception, and emotional instability. Horses are not fundamentally different.

Research shows that sleep restriction in horses can lead to:

Lack of REM sleep can have many negative consequences for horses. A "good nights sleep" is crucial for maintaining welfare.

• Reduced learning capacity

• Decreased performance over time

• Increased stress responses

• Higher sympathetic nervous system activation

• Disturbed gut microbiome

• Greater physical tension

  
  

In practical terms, this may look like:

• A horse that struggles to learn new exercises

• More resistance or frustration during training

• Subtle reactivity or tension under saddle

• A general feeling of being “not quite settled”

• Might be sensitive when touching their belly

  
  

When horses are unable to fully rest, their nervous system remains in a heightened state. The sympathetic system, the fight-or-flight response, stays more active than it should. Over time, this affects immune function, metabolism, and overall resilience.

Sleep is not just rest. It is regulation.

(Chokroverty, 2009, Smith, 2013, Hämäläinen et al., 2026b, Greening & McBride, 2022, (Gomes et al., 2025)

Why might a horse refuse to lie down?

Horses do not lie down when they do not feel safe or comfortable.

Common reasons include:

Pinning her ears as another horse passes and ultimately getting up. Unstable herd dynamics can reduce time spent laying down.

• An unstable herd dynamic

• A recent move or environmental stress

• Wet, hard, or insufficient bedding

• Limited space

• Social insecurity

• Physical discomfort or pain

  
  

If lowering and rising feels uncomfortable, especially through the back or pelvis, some horses will simply avoid lying down altogether.

Over time, that avoidance leads to cumulative sleep deprivation.

(Gobbo et al., 2025)

How can you improve your horses’ REM sleep?

A clear contrast between two resting behaviours: one horse lying down with her head on the ground in deep relaxation, while another pony dozes standing nearby.

Management plays a significant role.

Providing deep, dry, soft bedding makes lying down physically inviting. Space also matters. Some studies suggest that horses show a preference for sleeping outdoors in paddocks, likely because of available space and the presence of companions creating a sense of safety.

If you truly want to encourage healthy lying behaviour, consider:

• A dry, well-bedded resting area

• Enough space to move and lie comfortably

• A stable, predictable herd environment

• Monitoring for subtle signs of discomfort

Sleep is deeply connected to safety.

(Gobbo et al., 2025).

How do you know if your horse lies down enough and sleep enough?

Sometimes the signs are surprisingly simple.

You may find straw or wood shavings in the mane and tail. If your horse lives outside, they may come back covered in sand. In our paddock, I can often see the distinct lying patterns in the sand and, because our horses differ in size, I can roughly guess who rested where.

If you want to be certain, a stable camera can provide clear insight into sleeping behaviour, if your facility allows it.

But often, you also feel it.

A horse that sleeps well tends to feel mentally available, less reactive, and more able to process new information.

Is it a problem if they don’t lay down for a night?

An interesting study recently simulated a competition environment in which some horses did not lie down for three consecutive days. Those horses showed increased stress indicators, and riders noticed reduced learning ability during that period

(Barbosa et al., 2025).

This does not mean a single restless night will cause long-term harm. But it does show how quickly sleep affects performance and nervous system balance.

If your horse has recently moved, competed, or experienced stress, and you notice reduced focus or increased tension, it may simply be that they have not yet fully recovered.

Sleep is one of the clearest indicators of welfare.

A horse that feels safe in its environment and comfortable in its body will lie down. A horse that remains vigilant, uncomfortable, or tense will hesitate to do so.

And sometimes, when we look closely, sleep tells us more than performance ever could.

Sources

Greening, L., & McBride, S. (2022). A review of Equine Sleep: Implications for Equine Welfare. Frontiers in Veterinary Science, 9, 916737. https://doi.org/10.3389/fvets.2022.916737

Kelemen, Z., Grimm, H., Long, M., Auer, U., & Jenner, F. (2021). Recumbency as an Equine Welfare Indicator in Geriatric Horses and Horses with Chronic Orthopaedic Disease. Animals, 11(11), 3189. https://doi.org/10.3390/ani11113189

Hämäläinen, M. J., Brotherus, I. L., Wigren, H. M., Kaimio, T. E., Suomala, H., Olbricht, A., Hänninen, L. T., & Mykkänen, A. K. (2026). Effect of horse sleep behavior on performance in a field-side spatial reversal learning test. Scientific Reports, 16(1), 4265. https://doi.org/10.1038/s41598-025-34463-9

Chokroverty, S. (2009). Sleep deprivation and sleepiness. In Elsevier eBooks (pp. 22–28). https://doi.org/10.1016/b978-0-7506-7584-0.00003-3

Smith, H. (2013). Fibromyalgia/Chronic fatigue syndrome and sleep. In Elsevier eBooks (pp. 422–427). https://doi.org/10.1016/b978-0-12-378610-4.00485-x

Gobbo, E., Maccario, C., Šemrov, M. Z., Bovo, M., Atallah, E., Minero, M., & Costa, E. D. (2025). Exploring the impact of housing routine on lying behavior in horses measured with triaxial accelerometer. Frontiers in Veterinary Science, 12, 1572051. https://doi.org/10.3389/fvets.2025.1572051

Barbosa, Â. P., Oliveira, T. M., Seidel, S. R. T., Tokawa, P. K. A., Jaramillo, F. M., Roncati, N. V., & Baccarin, R. Y. A. (2025). Could restricting horses’ REM sleep improve dressage performance? Applied Animal Behaviour Science, 291, 106740. https://doi.org/10.1016/j.applanim.2025.106740

Gomes, A. R. C., Oliveira, T. M., Campos, G. G., & Baccarin, R. Y. A. (2025). Gut microbiota and sleep deprivation: Potential interactions and implications for equine Research – Scoping review. International Journal of Equine Science, 4(S1), 38–48. https://doi.org/10.64292/ijes.203