Horses require approximately 3 hours of recumbent (lying down) sleep daily for full REM sleep cycles. Sleep deprivation causes significant welfare compromise yet is commonly overlooked in equine management.
Horses can doze standing using the stay apparatus (passive ligament and muscle locking system), but REM sleep—essential for neurological health—only occurs during lateral recumbency. Horses typically lie down for 30-60 minutes in 2-3 sessions during the night. Factors preventing lying include: inadequate space to lie comfortably; fear of inability to rise (in horses with musculoskeletal pain or weakness); inadequate companionship (horses need to trust that another individual is watching while they sleep); and social dominance preventing lower-ranked horses from lying safely.
Sleep-deprived horses may demonstrate: sudden collapse—microsleeps causing the horse to buckle at the knees unexpectedly; wounds to the front of the knees from repeated microsleep stumbling; profound lethargy; reduced performance and responsiveness; and behavioural changes reflecting fatigue. These signs are often misdiagnosed as neurological disease or musculoskeletal problems before sleep deprivation is considered.
Addressing sleep deprivation requires identifying and removing the underlying cause. Solutions include: ensuring adequate stable or shelter size for lying comfortably (minimum 3.5m Ă— 3.5m for a horse); managing social groups to ensure subordinate horses can lie safely; treating pain conditions preventing safe lying; providing appropriate companionship; and reducing environmental stressors preventing sufficient nighttime rest. Video cameras provide objective assessment of whether horses are lying down overnight.
Sleep deprivation affects not only individual horse welfare but performance—fatigue from insufficient REM sleep impairs learning, responsiveness, and athletic function. Recognising sleep welfare as a component of overall equine welfare and performance improves management practices across disciplines. Equine welfare assessment should routinely consider sleep quality and opportunity, not only physical health parameters.