Horses are found in many different environments, but the one in which they evolved ranges from forest dwellers to plains grazers in the Miocene. They were last seen in the wild on the grassland plains of Eurasia. Feral horses in that type of environment, or domestic horses kept in pastures, spend the majority of their time grazing. Grazing is a behavior that consists of not only eating, but also selecting the patch on which to graze and the plants within that patch to harvest. Once selected, the horse must prehend the plant, usually by grasping it with his prehensile upper lip, ripping the plant from its roots with his incisors, then masticating the plant with his heavily ridged molars, and finally swallowing. After a few mouthfuls, the horse will take a few steps and select new plants. This behavioral pattern of slowly moving (several kilometers per day) and chewing (about 40,000 times per day) can be considered optimal for the horse's foot and gastrointestinal health. Horses salivate only when they are chewing. Saliva contains sodium bicarbonate, so every one of those chewing movements delivers a few milliliters of sodium bicarbonate solution to the stomach. Every step pushes blood out of the hoof and allows fresh blood to enter.
This behavior pattern must be compared to that of the typical modern domestic horse. He lives in a box stall and is fed a minimal amount of hay and maximal amount of grain. He is turned out (usually alone) into a paddock (usually grassless) for a variable period of time and ridden
(usually at speed), depending on the recreational purpose of the owner. The most valuable horses are kept in this manner and their welfare is probably the poorest as indicated by the rate of stereotypic behavior displayed and the rate of gastrointestinal problems (colic) and lamenesses reported. The stalled horse will spend 20% or less of his time eating. He may compensate somewhat for the absence of grazing by foraging through the bedding of his stall, sometimes eating the wood shavings that are typical bedding for horses. If wooden surfaces are available, he may chew them. This behavior is not a response to confinement, but rather a response to lack of dietary roughage, i.e., chewing time. Provision of free-choice hay, a bale a day for a 500-kilogram horse, increases the eating time of a stalled horse to approximately that of the grazing horse. The hay-fed horse may chew enough, but he does not move as frequently, nor does he have equine companions.
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