For horses, as for people, a hospital stay can be exhausting because the environment is so disruptive to sleep patterns—and the effect is even worse for those with arthritis. That’s what researchers in Brazil found in a recent study.

Horses can doze while standing, of course. But to achieve restorative rapid-eye movement (REM) sleep a horse must lie down in either sternal (propped up on his chest) or lateral recumbency (stretched out flat). In an optimal environment, horses spend between 8 and 15 percent of each 24-hour period lying down.

“The sleep pattern in horses is already well described,” says Tiago Oliveira, DVM, PhD, of the University of São Paulo, “but we are still studying which situations can influence this pattern and what is the consequence of this interference in the well-being and athletic performance of these animals.”

Researchers focus on REM sleep because it is so important to overall health, says Oliveira: “REM sleep is critical to the rest and recovery process for horses, as it is for all animals. Horses with total REM sleep deprivation can have collapses, falls and incoordination, causing great harm to their health and welfare.”

To study how a hospital environment can affect REM sleep in horses, Oliveira and fellow researchers hospitalized eight healthy mares for a five-day period. Each mare was also classified as having either mild or severe arthritis based on full lameness, radiographic and ultrasound exams.

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 videos of her activity. The researchers then reviewed the footage and documented several types of behavior, including wakefulness, duration of drowsiness and time spent in sternal and or lateral recumbency.

The data revealed that for the first two days of hospitalization, all the mares spent significantly less time than normal lying down. Those with mild arthritis resumed expected levels of recumbency on day three, but those with severe arthritic changes did not lie down for the normal periods of time until day four.

Although four days of interrupted sleep patterns may sound exhausting, Oliveira says the horses probably fared better than people would have in those conditions.

“We believe that the horses were adapting to the environment,” he explains. “Compared to humans, the horse can withstand longer periods without REM sleep without major damage because it is a prey animal in nature. This characteristic allows it to stay on alert longer, being essential for its survival. It is estimated that animals begin to experience greater impairment after a few days of total REM sleep deprivation.”

Overall, the researchers found that the mares with severe arthritis spent significantly less time lying down. In fact, those horses spent so little time in recumbency over the course of the study period that they could be considered sleep deprived. “The transition to recumbency was impeded by the arthritis—the movement of lying down and getting up was more uncomfortable than standing,” Oliveira says.

He adds that when horses remain on their feet, they are not only deprived of REM sleep but also risk overloading their vulnerable limbs. “Husbandry, injury treatment and pain control for these animals are very important in enabling proper rest, even in animals that apparently do not have pain while standing,” he says.

These findings under-score the importance of management measures that enable horses to obtain adequate REM sleep, says Oliveira, particularly when they have other physiological challenges. “Studies show several changes in husbandry (bedding 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