Kjellberg, L., Sassner, H., Yngvesson, J. 2022. Horses’ resting behaviour in shelters of varying size compared with single boxes. Applied Animal Behaviour Science 254, 105715.

Lying behaviour in horses is affected by factors such as bedding, housing and available lying area. For group-housed horses, social factors may influence access to available lying area and affect their ability to meet their need for sleep, including essential REM sleep. REM sleep can only be achieved when the whole body, including the head, is supported by the ground, so lateral recumbency is important to meet horses’ sleep requirements. This study investigated the effects of available lying area in shelters on horses’ lying and rising behaviour, on disturbance behaviour by horses, and on lying bouts by individual horses. Lying and rising behaviour was video-recorded for eight horses in single boxes (control treatment) and in an open-barn with three available lying area of 8, 18 and 28 m2/horse, respectively in the shelters. The results revealed significantly less lateral recumbency in the shelter with 8 m2 lying area/horse (22 min, p = 0.04) compared with the single boxes (52 min), and a tendency for more lateral recumbency with 18 m2 lying area/horse (48 min, p = 0.07) compared with 8 m2 lying area/horse. Rising without prior rolling was the most common rising behaviour in the single boxes. Frequency of rolling prior to rising varied from 14% to 55% for all housing systems, compared with previous observations of ~30% irrespective of available lying area. This may be due to inter-individual differences, indicating a need for detailed studies of rising behaviour. Lying behaviour was affected by the behaviour of other horses and also significantly affected by available lying area. With more available area in the shelter, horses lay down for almost twice as many bouts (p = 0.01) and for almost twice as long as compared to a smaller area (p = 0.001). Number of lying bouts (p = 0.001) and behaviour during rising from the lying position were also affected by available lying area. It is therefore likely that the space requirement to meet horses’ need for rest will be larger in group-housed horses than for horses in individual boxes.

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