Let sleeping horses lie: Researchers explore snoozing in older, lame equines

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Horses need to doze, and it's essential they get to lie down so they can achieve the required REM portion of their sleep cycle.
Horses need to doze, and it’s essential they get to lie down so they can achieve the required REM portion of their sleep cycle.

Neither age nor lameness arising from chronic orthopaedic disease significantly influenced the time that horses spent lying down in a recent Austrian study.

Adult horses sleep 2.5 to 5 hours a day, 80 percent of which is completed while standing. However, horses need to spend a minimum of 30 minutes lying down per day for the 3.5 to 4.5 minutes of REM sleep needed to achieve a full daily sleep cycle.

Horses, as a prey species, lie down only when they feel comfortable to do so. Horses that do not, or cannot, lie down for environmental reasons or because of discomfort, can suffer from REM sleep deficiency.

REM sleep deprivation can result in excessive secondary drowsiness and collapse, commonly incorrectly diagnosed as narcolepsy.

Researchers with the University of Veterinary Medicine Vienna set out to assess the influence of chronic orthopedic disease and old age on the time horses lie down.

Zsofia Kelemen and her fellow researchers fitted wearable automated sensor technology to 83 old and young adult horses at an animal sanctuary to measure the time spent lying down, moving, or standing. The horses comprised 39 warmbloods, 17 draft horses, and 27 horses of other breeds.

The study team was able to compare the daily time budgets of geriatric horses with and without chronic lameness to younger adult horses, both sound and lame.

The photograph, left, shows the skin lesions over the fetlock joints and carpi of a horse with chronic REM deficit. The other image shows a horse equipped with the automated equine monitoring system in the lycra bib. Photos: Kelemen et al. https://doi.org/10.3390/ani11113189

“Interestingly, neither age nor lameness due to chronic orthopedic disease significantly influenced the time spent lying down,” the researchers reported in the open-access journal Animals.

Recumbency times ranged from 0 to 319 minutes per day, with an overall average of 67.4 minutes. The average time budget for locomotion was 19.1%, while for standing (eating or resting) it was 75.6%.

Eight horses in the study were assessed as showing symptoms of REM deficit. “These horses had significantly shorter lying times and smaller locomotion time budgets than the other horses enrolled in this study, indicating a general compromise of well‐being,” the researchers reported.

The study team had expected that geriatric horses, and those with chronic orthopedic discomfort, would spend less time recumbent than healthy adult control horses. This was not the case with these horses.

“Geriatric horses and horses suffering from chronic orthopedic conditions can achieve recumbency times comparable to younger, healthy horses, but may require optimized husbandry conditions,” they said.

Neither pasture access nor housing conditions (single box stable versus group housing) significantly affected recumbency times. This, they said, may be because of the stable group composition and availability of adequate lying surfaces in the sanctuary.

The authors hailed the effectiveness of the wearable sensor technology, which they said can be employed to identify horses with short recumbency times at risk for REM sleep deficiency.

To identify potentially REM‐deficient horses, it proved essential to track them for more extended periods, to determine whether they do not lie down at all, or only do so when exhausted or under specific environmental conditions.

“For example, one horse with physical problems lying down due to severe osteoarthritis in both carpi did lie down on an incline in the pasture, which made it easier for the horse to get up.”

The researchers said the technology can be used to assess and monitor equine welfare objectively and optimize husbandry conditions so that old horses and those with chronic orthopedic conditions can achieve lying-down times comparable to younger, healthy horses.

The study team comprised Kelemen, Herwig Grimm, Mariessa Long, Ulrike Auer and Florien Jenner.

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

The study, published under a Creative Commons License, can be read here

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