Mutual grooming not only allows horses to reach areas that defy self-grooming strategies, but also facilitates exchange of odors² and has been shown to reduce heart rate when conducted in certain parts of the mane and withers.³ Grooming of withers by humans has a similar calming effect.⁴ The effects on cardiac function are particularly striking in foals, with a mean reduction of 14% in heart rate being reported when preferred areas were scratched by humans.³ This phenomenon is regularly harnessed by personnel who want to reward horses of any age without using food.

Mutual grooming can begin in the first week of life^5,6 but peaks in the second and third months of life,⁷ a period during which foals seem to find physical contact intensely gratifying. In the first instance the foal’s mutual grooming partner is its dam, who may dismiss other grooming partners if her foal solicits her attention by attempting to allogroom.⁵ Although some mature horses never allogroom, most regularly indulge in reciprocated activity of this sort with favored affiliates for periods of about three minutes at a time.⁸ Broadly speaking, regardless of their age, females spend more time mutually grooming than males. Mutual grooming partners are usually preferred associates that are close in social rank.⁹ In a natal band, mares and their offspring mutually groom kin rather than unrelated conspecifics.¹⁰ The absence of a stallion seems to bring with it some liberation in that grooming partners are preferentially from same sex-age groups.¹¹ The stallions in multi-stallion harems will mutually groom one another.¹²

Mutual grooming often starts at the cranial neck and proceeds to the withers (Fig. 10.1), the shoulders and then to the tail-head, sometimes changing sides (see Fig. 2.15).¹³ While youngsters often attempt to begin allogrooming, such overtures are rarely reciprocated by unrelated adults.⁵ As discussed in Chapter 5, there is equivocal evidence for the role of rank when a bout of mutual grooming begins.^5,11 Reports indicate that low-ranking individuals groom more and initiate more groomings and that allogrooming may have a role in appeasement.¹² However, most bouts are ended by the departure of the higher-ranking member of the dyad.⁵ Mutual grooming between foals is often observed before or after a bout of play.¹⁴

Figure 10.1 Mutual grooming helps equids to develop and maintain pair bonds.

(Photograph courtesy of Sandra Hannan.)

The frequency of mutual grooming is subject to daily and seasonal variation, with predictable troughs that coincide with recumbency.¹⁵ Shedding the winter coat and the seasonal peak in idling behavior account for annual peaks in mutual grooming (i.e. April and July in northern hemisphere studies⁵). When allowed to interact freely with other horses after 9 months of social deprivation, colts stabled singly showed significantly more social grooming than colts stabled in groups, which may reflect a build-up of motivation (a post-inhibitory rebound effect).¹⁶

Self-grooming brings out a great deal of resourcefulness in horses as they use their hooves, their mouths and objects in their environment to relieve irritation (Fig. 10.2). The frequency of self-grooming peaks at 12.3 times per hour in weeks 5–8 of a foal’s life.¹⁷ The relative proportion of body parts and the innate flexibility of foals both help to explain their relatively enhanced ability to self-groom and may account for the decline in frequency of self-grooming to 1.2–2.2 times per hour in adults.¹⁸ While their dams focus self-grooming on rolling and rubbing against the forelimbs, conspecifics or inanimate objects, foals are more frequently found scratching anteriorly with their hindlimbs or nibbling posteriorly.¹⁷

Figure 10.2 Grooming styles used by horses include rolling, shaking, rubbing, scratching and nibbling (of both the back and forelegs).

(Redrawn, with permission, from Waring.¹³)

Along with appetite and growth, pelage cycles are related to the duration of the photoperiod.¹⁸ Therefore the amount of self-grooming peaks with the shedding of the winter coat.

Scratching by humans can act as a highly valuable primary reinforcer, so an appreciation of the pleasure that grooming may bring can help to consolidate the horse–human bond. However, grooming by humans must take account of the variable sensitivity of different individuals and breeds.² The need to have a clean horse has been overstated by some horse-care manuals. Further, the perceived need to pull manes and tails undoubtedly irritates many horses and possibly compromises the horse–handler bond.

Rolling

Because preferred substrates are sand, fine dry soil and occasionally mud, horses at pasture tend to select bare patches on which to roll, often beside gates or water troughs.¹⁹ Some feral horses have been observed to roll preferentially in water.⁸ With more than 80% of rolling occurring where another horse has rolled,² its function is believed to include the opportunity to deposit scent over the body. The fact that horses, especially males,²⁰ smell chosen sites before and after rolling appears to support this view.

The head and neck help to propel the horse laterally while rolling (Fig. 10.3).¹³ Similarly, lateral flexion of the vertebral column and thrashing of hindlegs seems to help the horse to balance itself on the dorsal midline.¹³ Rolling horses usually return to the same side they started lying on but often repeat the roll before rising.¹³

Figure 10.3 (A) Sequence showing horse rolling. (B) After a bath horses seem more itchy than normal and enjoy rolling, especially in dusty substrates.

((A) Redrawn, with permission, from Waring.¹³)

The physical environment can affect horses’ inclination to get down onto the ground. For example, there is evidence that small boxes inhibit sternal recumbency.²¹ Apart from some foaling boxes, the space on the floor of most stables and many custom-built sand rolls is less than the width of most natural rolling sites. This helps to explain why we should be pleased that more horses do not get cast (stuck against the walls of stables or upside down in their stables). The use of anti-casting rails is a measure believed to help inverted horses to right themselves when stuck against the side of a stable. These rails are set about one meter from the floor, although their height should, strictly speaking, depend on that of the occupant. They work by providing some purchase against which the horse can push in a bid to move itself away from the wall.

Bedding materials such as straw that lend themselves to being banked up against the side of the stable wall are likely to reduce the risk of casting. Whatever bedding is selected must be managed carefully to maintain air hygiene. Beds that drain readily are less likely to be accompanied by high ammonia concentrations or allow humidity to rise to concentrations that increase the viability of fungal spores implicated in lower-airway disease.²² Bedding preference studies suggest that the appeal of straw depends on its being deep and is linked to its alternative use as a source of dietary fiber.^23,24

Nibbling and licking

The use of teeth in body care varies from a rhythmic scratching action by the upper incisors, to small bites. While the areas that can be reached by the teeth include the sides and loins (see self-mutilation in Ch. 11) and even the hindlegs (Fig. 10.4), the forelegs seem to receive especially detailed attention that incorporates considerable licking. This is a means of removing bot eggs from the hairs that effectively facilitates their ingestion. Although licking seldom occurs as part of mutual grooming,¹³ the licking of a neonate by its dam is probably the most important instance of a horse using its tongue during grooming a conspecific. This can last for 30 minutes and, as well as consolidating the mother–infant bond, it provides tactile stimuli that may have a role in stimulating responses such as standing. Licking by a stallion as part of courtship is a means of tasting rather than grooming.

Figure 10.4 Horses sometimes use their mouths to groom the hindlegs.

(Photograph courtesy of Francis Burton.)

A drowsing horse stands with its eyelids partly opened and its head hanging at a medium height (Fig. 10.7). The flexion of a single hindlimb is facilitated by the reciprocal apparatus in the hindlimb, which means that movements of the stifle joint drive those of the hock.³⁸ Thus, once the stifle is fixed in position, the hock is obliged to follow suit. In combination with the stay apparatus found in the forelimb as a means of supporting the fetlock, this allows the horse to remain upright with a minimum of muscular effort. The advantages of remaining standing include being able to achieve a quick escape if threatened, but also to avoid cardiorespiratory compromise that comes with recumbency. Interestingly, adopting certain postures for rest has been shown to have familial tendencies.³⁹

Figure 10.7 A horse’s posture changes in various states of activation: (A) resting with weight distributed among only three legs; (B) lying down; (C and D) recumbent resting attitudes; (E) arising.

(Redrawn, with permission, from Waring.¹³)

The distinction between drowsing and sleep necessitates understanding the different physiological characteristics of various states of wakefulness. In adult horses, sleep occupies 3–5 hours per day, while drowsing consumes a further 2 hours.⁴⁰ Postural changes tend to accompany certain states – for example, although the eyes remain partly open, the head gradually descends as the horse goes from drowsing to sleep.³⁶ Animals may rest without sleeping and while the distinction between drowsiness and sleep is reasonably subtle, since they may appear very similar externally, electrophysiological studies of animals in various stages of sensitivity to their environment have helped to unpick the differences. Although such measurements require subjects to be restrained, we can assume that the same differences apply in unrestrained horses. Using data extrapolated from restrained subjects, inferences can be made from the posture of horses indulging in various rest behaviors.

The two types of sleep clearly defined in horses are slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep (also known as deep or paradoxical sleep).⁴⁰ The electroencephalogram (EEG) waves of SWS, as the name suggests, are characterized by a low frequency, a feature that disappears as the horse drifts into REM sleep. Some muscular tone is retained in SWS, even when the head is resting on the ground during sternal recumbency. It is the only form of sleep that occurs in standing horses. Although it may increase in horses that are unable or reluctant to lie down, SWS cannot compensate for lost REM. This is illustrated by post-inhibitory rebound in REM sleep after periods without recumbency.⁴⁰ Along with the suggestion that horses do not lie down unless they are confident about their surroundings,^35,40 this accounts for some of the concerns for the welfare of horses that do not or cannot lie down.⁴¹

REM sleep was dubbed paradoxical because, while its EEG is similar to that of wakefulness (Fig. 10.8A), it has the highest arousal threshold. Cardiac and respiratory rates decrease in all forms of sleep.⁴² REM sleep is peculiar in that it involves the absence of postural tone (and therefore the eyes are shut). It occurs entirely during recumbency and is marked by the greatest degree of variability in cardiac and respiratory frequencies of any state, including wakefulness. As its name implies, REM sleep is also often accompanied by rapid eye movements. In REM sleep during lateral recumbency, limb movements, especially of the upper limbs, may occur.¹³

Stay updated, free articles. Join our Telegram channel

Join