For horses, as for humans, a hospital stay can be exhausting because the environment disrupts sleep patterns so much – and the effect is even worse for people with arthritis. This is what Brazilian researchers discovered in a recent study.
Horses can doze standing up, of course. But to achieve restorative REM sleep (REM), a horse must lie in sternal recumbency (leaning on its chest) or lateral recumbency (lying flat). In an optimal environment, horses spend between 8 and 15% of each 24 hour period lying down.
“The sleep pattern in horses is already well described,” says Tiago Oliveira, DVM, PhD, from the University of São Paulo, “but we are still studying what situations can influence this pattern and what is the consequence of this interference in welfare and athletic performance of these animals.
Researchers focus on REM sleep because it is so important to overall health, says Oliveira: “REM sleep is essential to the rest and recovery process in horses, as it is for all animals. Horses suffering from total REM sleep deprivation can experience collapses, falls and incoordination, which seriously impairs their health and well-being.
To study how a hospital environment can affect REM sleep in horses, Oliveira and his fellow researchers hospitalized eight healthy mares for a period of five days. Each mare was also categorized as suffering from mild or severe arthritis based on complete lameness, x-ray and ultrasound examinations.
Although the mares were hospitalized for study purposes only, they were kept on the same management schedule as horses admitted to the facility for diagnosis or treatment.
During the study period, cameras mounted in each mare’s stall continuously captured video of her activity. The researchers then examined the images and documented several types of behavior, including wakefulness, duration of sleepiness, and time spent in sternal and/or lateral recumbency.
The data revealed that during the first two days of hospitalization, all mares spent significantly less time than normal lying down. Those with mild arthritis returned to expected levels of recumbency on day three, but those with severe arthritic changes did not lie down during normal periods until day four.
Although four days of interrupted sleep might seem exhausting, Oliveira says the horses probably did better than people would have under those conditions.
“We think the horses were adapting to the environment,” he explains. “Compared to humans, the horse can endure longer periods without REM sleep without major damage because it is a prey animal in nature. This characteristic allows it to stay alert for longer, being essential for its survival. believes that animals begin to experience greater impairment after a few days of complete REM sleep deprivation.
Overall, the researchers found that mares with severe arthritis spent significantly less time lying down. In fact, these horses spent so little time in recumbency during the study period that they could be considered sleep deprived. “The transition to recumbency was hampered by arthritis – the motion of lying down and getting up was more uncomfortable than standing up,” says Oliveira.
He adds that when horses are left standing, they are not only deprived of REM sleep but also risk overloading their vulnerable limbs. “The husbandry, treatment of injuries, and pain control of these animals are very important to allow adequate rest, even in animals that apparently feel no pain when standing,” he says.
These findings underscore the importance of management measures that allow horses to achieve adequate REM sleep, Oliveira says, especially when they have other physiological challenges. “Studies show that several changes in husbandry (bed depth, lights on, space to lie down) can improve horses’ rest,” he says. “If the horse has a chronic disease, it is very important to follow up with a veterinarian to promote comfort and allow the animal to express its natural behaviors.”
Reference: “Hospitalization and disease severity alter the resting pattern of horses,” Journal of Equine Veterinary Science, December 2021