The effect of altering routine husbandry factors on sleep duration and memory consolidation in the horse

Recumbency as an Equine Welfare Indicator in Geriatric Horses and Horses with Chronic Orthopaedic Disease

“…Recumbency is a prerequisite for horses achieving rapid eye movement (REM) sleep and complete a full sleep cycle [ 1 , 2 , 3 , 4 ]. While adult horses sleep only 2.5–5 h/day, 80% of which is in a standing position, they need a minimum of 30 min of recumbency per day to achieve 3.5–4.5 min of REM sleep and avoid REM sleep deprivation with excessive secondary drowsiness and collapse [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. However, as a prey species, horses only lie down when they feel comfortable to do so [ 2 , 4 , 5 , 14 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”

“…While adult horses sleep only 2.5–5 h/day, 80% of which is in a standing position, they need a minimum of 30 min of recumbency per day to achieve 3.5–4.5 min of REM sleep and avoid REM sleep deprivation with excessive secondary drowsiness and collapse [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. However, as a prey species, horses only lie down when they feel comfortable to do so [ 2 , 4 , 5 , 14 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Hence, measuring lying behavior is an essential component of equine welfare assessment [ 12 , 13 ].…”

“…Sleep is a basic maintenance behavior, essential for physiological and cognitive function. Horses sleep in a polyphasic pattern, distributed over 5–7 episodes, with most sleep occurring between midnight and 4:00 am [ 2 , 3 , 4 , 5 , 8 , 10 , 12 , 14 , 32 , 33 , 34 , 35 , 36 , 37 ]. Based on postural and behavioral indicators and specific cortical electronic activity, four sleep–wakefulness states are differentiated: wakefulness (18 h/d [ 3 ]), drowsiness (2 h/d [ 3 ]), slow-wave sleep (SWS, 3 h/d [ 3 ]), and paradoxical or rapid eye movement (REM) sleep (<1 h/d [ 3 ]) with only the latter two counting toward the total sleep time budget of typically 2.9–3.5 h/d (10–21% of the total daily time budget) [ 3 , 5 , 6 , 7 , 8 , 12 , 16 , 31 , 32 , 33 , 38 , 39 , 40 ].…”

“…REM sleep represents the smallest proportion (10–15%) of the total sleep time, while SWS, at 65% takes up most sleep time [ 4 , 5 , 7 ]. While sleep in horses, in contrast to most other species, is not uniquely associated with recumbency, as horses can go through SWS in both standing and recumbent positions, the muscle atonia associated with REM sleep requires sternal or lateral recumbency [ 1 , 2 , 3 , 4 , 5 , 7 , 11 , 14 , 16 , 31 ]. Indeed, since horses usually fall asleep shortly after lying down, recumbency can be used as an inferred measure of sleep [ 7 , 11 , 12 , 16 ].…”

“…Polysomnographic studies demonstrated that horses were in REM sleep 29.7% of the time spent sleeping in sternal and 33.7% of the time in lateral recumbency, with SWS accounting for the remaining time [ 16 , 39 ]. As a reduction in recumbent sleep states cannot be compensated for by increased sleep time standing, the reluctance of a horse to enter a recumbent position causes REM sleep deficiency and can have substantial effects on health and quality of life [ 14 ].…”