The influence of bedding on the time horses spend recumbent

To determine if bedding has any influence on the time horses spend recumbent, 8 horses kept on straw and 8 kept on wood shavings were observed from 10:00 to 5:30 for two successive nights. Observations were conducted using time-lapse video recordings. Lying down and rising behavior, as well as frequency and duration of bouts spent in lateral and sternal recumbency, was registered. The results showed that horses on straw were lying in lateral recumbency three times longer than horses on shavings (P < .001), whereas the time horses spent in sternal recumbency did not differ. The longest period of noninterrupted lateral recumbency was longer for horses on straw than for those on shavings. Because horses must lie down, preferably in lateral recumbency, to achieve paradoxical sleep, the reduced time spent in lateral recumbency in horses on wood shavings may affect their welfare and performance. Independent of the bedding, we further observed that, as the horses got up from recumbency, most of them made attempts to roll over before rising. This behavior appeared to be caused by some difficulty in rising, possibly due to the box size, and might have a connection with the fact that horses sometimes get stuck against the box wall.

Introduction

Many riding horses spend the majority of their life in an artificial environment. Horse owners keep their horses under certain conditions because of tradition, because they want to make the horse feel comfortable from a human point of view, or to reduce the amount of work involved in horse husbandry. Often the choice of bedding substrate is made from a subjective point of view without assessing both short-term and long-term effects of the bedding. Part of the reason is that only few studies have analyzed horses' preferences for different bedding substrates and their effect on the time horses spend recumbent. In one study comparing straw and wood shavings, no significant preference was found.1] In another study comparing plastic, wheat straw, and wood shavings, the time horses spent standing, sleeping, or lying down was not affected significantly by the bedding substrates. 2] Mills et al 3] found that horses, given a choice between straw and wood shavings, spent significantly more time on straw. Whereas the substrates had no significant effect on behaviors such as eating, lying, and standing alert, horses spent more time performing bedding-directed behaviors on straw but more time dozing on shavings. Finally, it has been reported that the use of nonstraw bedding may increase the risk of abnormal behaviors such as weaving. 4]As far as bedding properties are concerned, Airaksinen et al5] concluded that air quality in the stable and utilization of manure can be improved by selecting a good bedding material. According to Reed and Redhead, 6] both straw and shavings are economical and easy to obtain, and they make a bright, comfortable bed. Straw bales are convenient to store, but may be eaten by the horse, are labor intensive, and may be dusty or contain fungal spores. Wood shavings are not eaten by the horse and are good for respiratory problems but need to be kept very clean because they are porous. In addition, they are not as warm as straw because they do not trap air the way straw does.Electroencephalographic (EEG) studies in cats have demonstrated that sleep can be divided into two stages of differing electrocorticographic (EcoG) patterns, ie, slow-wave-sleep (SWS) and paradoxical sleep (PS).7] During PS, bursts of rapid eye movements (REM) can be seen at irregular intervals. 8] In humans, dreaming occurs during this stage. 9 and 10] Horses are able to sleep while standing, 11] but in this position they only go into SWS. 14, 15 and 16] During PS there is a complete abolition of muscular tone of antigravity muscles and of neck muscles, as shown in cats. 17] In horses, there is a gradual loss of muscular tone until the middle of the recorded SWS period, whence it decreases to a negligible amount during PS. 15] Consequently, muscular tone disappears entirely at the onset of PS. 18] Horses are unable to complete a sleeping cycle without lying down to enter PS. 8, 19 and 20] They normally fall asleep while standing and, when they feel confident about their environment, lie down in sternocostal recumbency. 8] Thereafter, they proceed to lateral recumbency and enter PS. 14 and 19] Dallaire and Ruckebusch 18] demonstrated that the SWS state was infrequent in the standing animal and most often occurred during sternocostal recumbency with the head resting or not on the ground. PS occurred in both sternocostal and lateral recumbency, although the animal frequently had to readjust its position into sternocostal recumbency due to the disappearance of neck muscular tone.The sleep pattern of horses depends on many circumstances, such as age,21, 22 and 23] diet, 16] and familiarity with the environment. When horses are put outdoors it may take some days before they lie down. If one horse that is familiar with the environment lies down, the others usually follow. 8 and 13] Dallaire and Ruckebusch 16] subjected three horses to a four-day period of perceptual (visual and auditive) deprivation. After this period total sleep time increased due to an augmentation of both SWS and PS. Finally, there is large individual variation between horses in the time they spend recumbent and sleeping. 15]Horses spend 11% to 20% of the total time in recumbency.11 and 15] Lateral recumbency represents about 20% of total recumbency time, and uninterrupted periods of lateral recumbency vary from 1 to 13 minutes (mean, 4.6 min). 14 and 16] Steinhart 11] found that the mean length of uninterrupted lateral recumbency periods was 23 minutes, the longest period being one hour. Total sleeping time in the stabled horse averages 3 to 5 hours per day or 15% of the total time. 8, 13 and 16] Keiper and Keenan 24] found similar time budgets in feral horses that were recumbent approximately 26% of the night. PS is about 17% to 25% of total sleeping time, and the mean length of a single PS period is 4 to 4.8 minutes. 13 and 18]In stabled horses sleep is mainly nocturnal and occurs during three to seven periods during the night.8, 13 and 16] Ruckebusch 13] observed that neither sleep nor recumbency occurred during daytime in three ponies observed for a month and, in another experiment conducted on horses, PS occurred only during nighttime. 15] A group of ponies observed for more than a month between 8:45 and 4:45 spent only 1% of the daytime recumbent.25] The maximum concentration of sleep occurs from 12:00 to 4:00 .8, 16, 18 and 24]The purpose of this study was to examine two groups of horses in a familiar environment, one group kept on a bedding consisting of straw, and the other kept on wood shavings, and to determine if there was any difference between the two groups in the time they spend recumbent.

Materials and methods

Housing. The study was conducted in one of the biggest riding clubs in Denmark, housing about 150 horses. The 18 horses used in the study stood in three different parts of the stable. They were all stabled in boxes measuring 3 × 3 m and subjected to the same feeding and management routine. They were unable to see their next-door neighbor because of a tall wooden board, but they were able to see the horses stabled on the opposite side of the corridor through bars. Nine horses were stabled on wheat straw (15 cm long, dry matter content 87-88%) and nine on oven-dried wood shavings (80% spruce and 20% pine, dry matter content 82%).Animals. All horses used in the study were privately owned. They had been kept in the boxes in which they were observed a minimum of three weeks. Three of the horses were mares and 15 were geldings. Most of them were Danish Warmblood used for dressage riding. Their ages ranged from 5 to 18 years (mean, 10.6 y) and their height ranged from 1.60 to 1.76 m (mean, 1.68 m). All horses wore a blanket. Age and sex distribution between the two groups is shown in Table 1.