Equine Sleep

Equine Sleep

Compared to other mammals, horses sleep relatively little with approximately a total sleep time of 5 hours, just 3 hours of sleep laying down and 30 minutes of paradoxical sleep (or REM) within any 24 hour period [1]. However, due to domesticated management practices, housing arrangements and environmental insecurity, the horse faces many challenges which regularly disrupt their natural sleep pattern [3,5]. These challenges include short stays at shows, the vets or the racetrack and housing conditions which are either too small, unfamiliar, uncomfortable or contain a threat [3,10].We know as humans how problematic lack of sleep can become for daily functioning, mental health and physical health. So is this the case for our horses too?

Sleep Deprivation in the horse

It is not fully known to what extent sleep deprivation can detriment the horse, as compared to other species, it is a difficult condition to recreate and monitor in an experimental setting. Nevertheless, from what we have learnt from studies in humans, other animals and observations of a sleep deprived horse, it can be assumed that it causes some discomfort, distress and impaired biomechanical function. Studies in humans and in particular, athletes, show that not only is performance affected due to sleep deprived consequences such as changes in metabolism, appetite, and protein synthesis but brain associated functions such as learning, memory, pain, perception, immunity and inflammation [4]. These correlate with findings from other animal studies in cats, dogs and rats where additional outcomes included prolonged muscle fatigue, weight loss, a reduction in red blood cells and reduced ability to regulate body temperature [7].

Some of these, such as prolonged muscle fatigue and inflammation could be particularly problematic for the horse due to lengthy periods of standing, short recumbency duration and slower glycogen uptake in fatigued muscles along with sustained periods of immobility due to inadequate domestic housing conditions [11]. Furthermore, horses are renowned for their unique ability to thermoregulate against the elements and could potentially suffer if compromised with sleep deprivation and were not able to do so as effectively.

Early studies between equine sleep deprivation and performance already confirm similarities with human research. In 2015, Dumbell monitored horses for standing and recumbent sleep before performing in a showjumping round two days later. This revealed that slower jumping rounds and a greater number of faults were observed in horses seen to spend less time in standing and recumbent positions than those displaying more frequent bouts of sleep [6]. Dumbell suggests although there were no significant correlations, equine sleep requires further investigation to identify its role as a management factor to monitor performance. Especially as sleep deprivation in horses has been described as relatively ‘common’ [9].

Although it may hinder performance, sleep deprivation is generally not a huge threat to the horse’s health, as naturally, they can go days without full sleep cycles due to their predatory status in the wild [5]. In most cases, normal sleep pattern tends to resume fairly quickly and the sleep-deprived horse has been deemed safe to ride although it is recommended they are seen by a vet prior to recommencing work after displaying sign of sleep deprivation [5]. These signs include excessive daytime sleepiness whereby the horse sways and lowers his head, sometimes looking as though his legs might buckle [9]. Further indications of buckling and collapsing are ‘chronic, recurrent abrasions over the front of the fetlocks, and the front knees [8]. Click here to see what sleep deprivation looks like.

How can I tell if my horse is getting enough sleep?

Good question. Sleep is not an easy thing to monitor in the horse. However, if they are regularly laying down, we can only assume without further investigation that they are getting some proper sleep. Normal signs include compacted patches of bedding and stains or pieces of bedding on the horse's body or rug. If concerned, you could also use video recording of their stable and spend time rewinding to check for recumbent behaviour. 

As we believe sleep is a crucial factor to monitor for good health, our Trackener app detects sleep by identifying between sternal and lateral recumbency and logging sleep behaviour around the clock. So far, our findings (from over 4000 hours of data) correlate with scientific results, with most horses sleeping for 2-5 hours between 12am and 4am but also during the evening between 7pm and 11pm. Shown below is an image of the app and how this information is displayed with time of day at the bottom and duration of each position along the side. For more information on how the app works, read more here.

A screenshot from the Trackener Life App
Key: Lying on side = Lateral recumbency
         Lying straight = Sternal recumbency

Why might my horse have sleep deprivation and what can I do?

Turnout

• Your horse may be lonely – Add another horse to their turnout for company or move him/her to a more heavily populated area so there are plenty of horses in sight [5].
• There may be something wrong within the social group – change the group around or remove a potential aggressor [5].
• There may be a threat such as excessive noise that is causing distress and making him feel unsafe e.g.- a train track or shooting ground nearby. Try where possible to eliminate the cause of fear if you suspect this is the case [5,9].

Stabling

• Your horse may not have enough room -Increase stable size. Research has shown horses prefer larger stables for laying down, particularly as they like to roll when laying down/getting up [12].
• Your horse may not feel comfortable -Try a different type of bedding. Straw has repeatedly proven to result in the highest frequency of recumbent behaviour from horses over wood shavings and straw pellets [13] 

Health

• Your horse might be in pain - Horses suffering from medical conditions such as multiple degenerative joint disease (older horses), old fractures, chronic colic and neurologic disease may find it uncomfortable getting up and down and therefore avoid it [9,12].
• Sterotypies – If your horse has a stereotypy, it may be affecting their ability to sleep. Research found that "crib-biting" horses had a 48% reduction in standing sleep time compared to "non-crib-biting" horses [14].

As our horse's preferences and temperaments are all very individual, it's difficult to know exactly what may be causing a change in sleep pattern. However, being aware of sleep, regular monitoring and knowing what is normal for your horse(s) can help identify these changes early on so that a solution can be found to redeem normal sleep behaviour. Whether your horse is retired, a happy hacker, local show horse or competing at the top, sleep could soon become a key health factor for well-being and performance as research develops. What do you think?

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Written by Ruth Box BSc, EEBW @ruth_box6910 Email Ruth

Further Reading

Study Evaluates Cribbers’ Sleeping Habits

British researchers found horses that crib spend less time in “standing sleep” mode than horses that don’t.

Sleep and Sleep Disorders in Horses, AAEP 2008

Unlike humans, adult horses average only about three to five hours of sleep per day, with sleep events occurring intermittently throughout the day and night, with most occurring at night. Lack of sleep or a sleep disorder has the potential to impact

Understanding narcolepsy in horses

"A rare and incurable sleep disorder of the central nervous system (CNS). It is characterised by spontaneous “sleep attacks” at inappropriate times – usually accompanied by an uncontrollable loss of muscle tone."

References

[1] Williams, D. C., Aleman, M., Holliday, T. A., Fletcher, D. J., Tharp, B., Kass, P. H., ... & LeCouteur, R. A. (2008). Qualitative and quantitative characteristics of the electroencephalogram in normal horses during spontaneous drowsiness and sleep. Journal of veterinary internal medicine, 22(3), 630-638.
[2] Zepelin, H., Siegel, J. M., & Tobler, I. (2005). Mammalian sleep. Principles and practice of sleep medicine, 4, 91-100.
[3] Greening, L., Shenton, V., Wilcockson, K., & Swanson, J. (2013). Investigating duration of nocturnal ingestive and sleep behaviors of horses bedded on straw versus shavings. Journal of Veterinary Behavior: Clinical Applications and Research, 8(2), 82-86.
[4] Halson, S. L. (2014). Sleep in elite athletes and nutritional interventions to enhance sleep. Sports Medicine, 44(1), 13-23.
[5] Bertone JJ. Excessive drowsiness secondary to recumbent sleep deprivation in two horses. Vet Clin North Am [Equine. Pract] 2006;22:157–162. 13
Accessible from https://thehorse.com/121155/understanding-equine-sleep-deprivation/
[6] Colley S., Murphy M., Dumbell L., Greening L. (2015)
A preliminary investigation of competition performance linked to duration and frequency of nocturnal sleep behaviours In Heleski C., Merkies K. (Eds.), 11th International Society of Equitation Science Conference (p. 36). Vancouver: ISES
Accessible from https://thehorse.com/113655/equine-sleep-patterns-effects-on-performance/
[7] Rechtschaffen, A., Bergmann, B. M., Everson, C. A., Kushida, C. A., & Gilliland, M. A. (1989). Sleep deprivation in the rat: X. Integration and discussion of the findings. Sleep, 12(1), 68-87.
[8] Loving, N.S. (2009) Sleep and Sleep Disorders in Horses, AAEP 2008 Accessible at:
https://thehorse.com/124308/sleep-and-sleep-disorders-in-horses-aaep-2008/
[9] Monica Aleman, M. V. Z., Williams, D. C., & Holliday, T. (2008) Sleep and Sleep Disorders in Horses. AAEP PROCEEDINGS. Vol.54, 180 - 185.
[10] Belling Jr, T. H. (1990). Sleep patterns in the horse. Equine Practice, 12, 2-26.
[11] Waller, A. P., & Lindinger, M. I. (2010). Nutritional aspects of post exercise skeletal muscle glycogen synthesis in horses: a comparative review. Equine veterinary journal, 42(3), 274-281.
[12] Raabymagle, P., & Ladewig, J. (2006). Lying behavior in horses in relation to box size. Journal of Equine Veterinary Science, 26(1), 11-17.
[13] Werhahn, H., Hessel, E. F., Bachhausen, I., & Van den Weghe, H. F. (2010). Effects of different bedding materials on the behavior of horses housed in single stalls. Journal of equine veterinary science, 30(8), 425-431.
[14] https://thehorse.com/115053/study-evaluates-cribbers-sleeping-habits/