Is your horse getting enough sleep?

Horses may not need as much sleep as humans, but getting sufficient, quality rest is still crucial for their overall health and well-being.

While horses are able to sleep while standing, thanks to their specialised stay apparatus, they can only experience REM sleep when lying down, allowing their muscles to fully relax.

Several factors can interfere with a horse’s ability to get enough restful sleep, leading to signs of sleep deprivation. These factors include pain, injury, health issues, noisy or overly bright barn environments, and even the horse’s position in the social hierarchy.

Although equine sleep disorders are not yet well understood, horse owners should familiarise themselves with the symptoms of sleep deprivation in horses and take steps to enhance their horse's sleep quality.

This article will explore the latest understanding of equine sleep patterns, as well as some causes and symptoms, and when to seek help.

Equine Sleep Cycles

While limited information is available about equine sleep behaviour, studies indicate that horses go through various sleep patterns and are unable to experience the full range of sleep cycles while standing (Belling, 1990).

Similar to humans, horses progress through multiple sleep cycles, which include different stages such as rapid eye movement (REM) and non-rapid eye movement (NREM) sleep (Peever at al., 2017).

NREM Sleep

Researchers classify NREM sleep into four stages (N1–N4) based on brainwave activity, representing the progression from wakefulness to deep sleep. Beta waves indicate full wakefulness, while slower alpha waves signal relaxation. As horses enter N1 sleep, brain activity shifts to theta waves, often accompanied by a lowered head, semi-closed eyes, and a droopy lip (Huang et al., 2021).

N2 marks full sleep onset with increased theta wave activity, a stage commonly seen in both humans and horses. The deeper stages, N3 and N4, are characterized by slow, high-amplitude delta waves. While researchers have observed N3 sleep in horses, N4 has not been detected (Greening et al., 2022).

Equine Stay Apparatus

Horses can enter light NREM sleep while standing, thanks to a specialised system called the stay apparatus. This structure, made up of ligaments and tendons, allows horses to remain upright with minimal muscle effort by locking major joints and stabilising the limbs, preventing the horse from losing balance (Hermanson et al., 1991).

Passive Stay Apparatus

In the front limbs, the passive stay apparatus involves the shoulder, biceps, elbow, and triceps. The biceps muscle prevents shoulder flexion, while the triceps fixes the elbow. The Lacertus fibrosus tendon locks the limb without muscle use, while flexor tendons and ligaments prevent overextension of lower joints.

Pelvic Stay Apparatus

In the hind limbs, the stay apparatus stabilises the stifle, hock, and lower joints. Locking the stifle also stabilises the hock through the reciprocal mechanism, allowing the joints to work together. This system enables horses to support their body weight effortlessly, shifting weight and resting one hind leg at a time (Schumann et al., 2003).

Why Won’t My Horse Lie Down to Sleep?

Horses may avoid lying down to sleep for several reasons. They might feel uncomfortable due to inadequate bedding, a small stall, or being separated from other horses. Pain or stress is the most common cause of sleep deprivation in horses and can also be contribute toward not wanting to lie down (Kelemen, 2021). If your horse isn’t lying down to rest, assess their environment and consult a veterinarian to check for potential sleep disorders or underlying issues.

Signs of Sleep Deprivation in Horses

Sleep deprivation in horses is a serious welfare issue, leading to increased stress and a higher risk of health complications. One major concern is that sleep-deprived horses may collapse during REM sleep while standing, posing a danger to both the horse and handlers.

Symptoms of sleep deprivation can take up to two weeks to appear and vary between horses.

Common signs include (Greening et al., 2022)

• Collapsing into a bowing position

• Sudden complete collapse

• Lack of shavings on the horse’s tail or blanket, indicating they haven’t been lying down

• Unexplained injuries to the fetlock, knee, or face

• Increased daytime drowsiness

• Hyper-vigilance

• Poor performance

Monitoring your horse with a stall or paddock camera can help track how often they are lying down to sleep.

References: Belling, T. Sleep Patterns in the Horse. Equine Practice. 1990. Peever, J. et al. The Biology of REM Sleep. Current Biol. 2017.

Huang, H. et al. EEG-Based Sleep Staging Analysis with Functional Connectivity. Sensor (Basel). 2021.

Greening, L. et al. A Review of Equine Sleep: Implications for Equine Welfare. Front Vet Sci. 2022.

Hermanson, J. et al. Evolutionary and functional morphology of the shoulder region and stay apparatus in fossil and extant horses. J Vertevr Paleontol. 1991

Schumann, S. et al. The equine hind limb is actively stabilized during standing. J Anat. 2003

Kelemen, Z. Recumbency as an Equine Welfare Indicator in Geriatric Horses and Horses with Chronic Orthopaedic Disease. Animals. 2021