Equine Maintenance Behavior: Feeding, Drinking, Coat Care and Behavioral Thermoregulation
Katherine Albro Houpt
Laboratory of Equine Behavior and Welfare, College of Veterinary Medicine
Cornell University, Ithaca, New York 14853-6401 USA
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The maintenance behavior of horses falls into four general areas: ingestive behaviors, coat care, thermoregulation, and rest. Ingestive behaviors include eating, drinking, and procurement of salt. Coat care includes auto- and allo-grooming. Behavioral thermoregulation includes both means of conserving heat in cold weather and means of dissipating heat in hot weather. Autogrooming consists of tail swishing, rolling, rubbing on inanimate objects or rubbing one part of the body on the other. For example, horses will rub their heads on their forelegs and young (or limber) horses will scratch their head and ears with their hind limb. Self-grooming can include rubbing or using the head to swipe at the body. Mutual grooming involves grasping a fold of the partner’s skin with the teeth.
Feeding behavior by feral (Salter and Hudson, 1979; Keiper and Keenan, 1980; Rubenstein, 1981; Duncan, 1985), wild (Boyd, 2002), and pastured horses (Crowell Davis et al, 1985) is primarily grazing. Grazing is not just ingesting grass, but consists of appetitive and consumptive phases. The horse must select the area - called a feeding station - in which to graze, prehend the stems with his prehensile upper lip, bite it off, chew and swallow it. He may bite 30,000 times per day (Mayes and Duncan, 1986). He will take a few bites and then walk a few steps to the next feeding station. This behavior occupies the majority of his time, but consists of exercise as well as feeding. The amount of time spent grazing varies with the season, with the age and sex of the horse, and with the herbage availability. When grass is scarce horses will browse on branches of trees, eat seaweed, and may become coprophagic. Stabled horses fed free choice hay spend almost as much time eating as free ranging ones (Houpt et al, 2001), but reduction of hay and substitution of grain or pelleted feed reduces feeding time considerably and may lead to physical and behavioral abnormalities (Ralston et al, 1979).
Sleep in horses has not been studied extensively, because of the difficulty of obtaining electroencephalograms from the head of an animal with large jaw and facial muscles (Dallaire and Ruckebusch, 1974). The few physiological studies have been supplemented with more numerous observational ones. Observational studies reveal that horses stand with a hind limb flexed, their head lowered and their eyes half closed for two to four hours per day (Ruckebusch, 1972). This posture is believed to indicate that the horse is in slow wave sleep. In order to enter Rapid Eye Movement (REM) sleep, the horse must lie down because of the lack of muscle tone in that stage of sleep. When horses cannot lie down, they may lean or otherwise support their weight when they enter that stage of sleep. Recumbent rest (presumably REM sleep) occupies more of the foal’s time budget than that of the adult. There is a gradual decrease with age. Two year olds lie down more than adults (Boy and Duncan, 1979).
Rolling is a behavior that may be related to coat care or general comfort behavior. It is the only way a single horse can rub the dorsal surface of the body. In order to roll, the horse will first lower his head, sniff the ground, and often paw. Then he will flex all four limbs and sink to the ground to one side or the other. He may roll from side to side or remain on one side. If he doesn't roll to a second side, he may arise and lie down again with the second side down. When a normal healthy horse has rolled, he will shake, dislodging some of the soil that clings to his coat. Rolling may also have a marking function because stallions roll more than mares. Although foals perform other forms of self grooming more than adults, they roll less.
Horses switch their tails for two reasons--coat care and aggression. Tactile stimuli produced by insects, especially biting flies, result in the fly swishing response. Horse tails are rarely docked now in Europe or North American except for some breeds of show horse. In some countries, docking or cutting the tail so it is less than 20 cm long is common especially for harness horses or horses whose saddles are stabilized by a crupper. Flies can also be dislodged if they stimulate the panniculus response in which the skin is shaken. This might be a more frequent response in docked horses. A final response to external irritation is a simple swipe of the muzzle across the skin of the side or chest, presumably to brush off the irritating stimulus.
Horses rub their heads against their own front limbs or other objects. This is frequently seen when a horse, sweating after strenuous exercise, rubs his head on a person. Some rubbing is normal, but an increase in frequency or duration of rubbing may indicate a health problem. External parasites, especially lice or dermatitis, can produce pruritus to which the horse responds by rubbing. Horses will rub their heads or their rumps against solid inanimate objects.
Horses also allogroom or mutually groom (Clutton-Brock et al, 1976). They either stand in reverse parallel position and swish flies from one another's face and forequarters or they stand in reverse parallel position and groom one another, usually on the back or withers. A facial gesture that signals intention to groom has not been identified nor has the signal that causes the horse to change sides so that a horse that was grooming the right side of his partner now grooms the left. Mares spend more time allogrooming than stallions, and fillies spend more time allogrooming than colts. Among adults, the grooming partner is usually the preferred associate and close in social rank. Stallions do allogroom but mostly as a form of courtship, and this type of grooming is not reciprocated by the mare. Occasionally unidirectional grooming is observed in other horses usually young horses. Mutual grooming is most common in the spring when the winter coat is being shed. The seasonal pattern indicates that the horses are reacting to the discomfort of a thick coat in warm weather or to changes in day length.
Most species, such as swine, tend to clump in cold weather; in contrast, horses stand closer together in the summer presumably to take advantage of one another's tails for protection from flies. Another strategy is to stand in water or on barren patches of ground (Duncan and Cowtan, 1980). In some climates, patches of snow remain even in the summer and horses will stand there to avoid insects (Keiper and Berger, 1982). To avoid direct solar radiation, they will stand in the shade during the warmest parts of the day (Crowell-Davis, 1994). When a water source is nearby, the number of drinking bouts per day is proportional to the environmental temperature (Crowell-Davis et al, 1985). Horses spend more time grazing in the winter both because herbage is scarce and because their caloric needs are greater in the cold (Tyler, 1972). Horses will face away from wind and seek shelter particularly in wet weather (Boyd and Houpt, 1994).
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