Could restricting horses' REM sleep improve dressage performance?

Abstract

The relationship between athletic performance and sleep deprivation is well-described in human medicine. Little is known about whether sleep deprivation affects the horses’ athletic performance. Previous studies show how changing environment, such as hospitals, can alter sleep patterns in horses, decreasing their total rapid eye movement (REM) during sleep time. Periods of REM sleep deprivation are frequently encountered in the management of athletic horses, particularly during transportation and temporary stabling at competitions. The objective of this study was to evaluate whether an association exists between athletic performance, welfare, and sleep deprivation in horses subject to potential REM sleep deprivation. The horses in this study were placed in a simulation of a competition setting, in which the horses did not laydown. A randomized crossover study simulating a competition outside from home was performed using ten dressage athletes Lusitano Pure Breed horses, aged 4–7 years, divided into two groups: sleep deprivation and control. All animals were observed in both conditions. REM sleep deprivation was accomplished by preventing horses from entering sternal or lateral recumbency for three consecutive days (72 h). The Horse Grimace Scale (HGS) was used in the morning and afternoon. Salivary cortisol was collected once daily at 10 a.m. Heart rate variability (HRV) was measured once daily for 7 min using a frequency meter. After 72 h, the horses participated in a voluntary approach test and a test competition, with scores from judges based on FEI young horses test competition and a questionnaire for riders. Sleep deprivation did not affect horses’ physical performance when comparing the judges’ scores. Judges’ scores in the dressage competition had weak reliability. The riders were not able to identify with accuracy sleep deprived animals; however, some riders described their horses with lower level of focus or tired when sleep deprived. HGS is a valuable tool in the measurement of acute pain in horses, but it is not sufficiently sensitive to identify REM sleep alteration. HRV and salivary cortisol concentration did not change in horses subjected to REM sleep deprivation. Irritability and reluctance in horses with sleep deprivation should be further investigated in larger groups. There were no marked alterations in the parameters evaluated regarding REM sleep interference in horses, and there was no notable change in test competition scores, indicating that short sleep pattern interference does not affect their athletic performance. However, sleep pattern interference may link to changes in their focus during exercise.