Horse behavior is best understood from the view that horses are prey animals with a well-developed fight-or-flight response. Their first reaction to a threat is often to flee, although sometimes they stand their ground and defend themselves or their offspring in cases where flight is untenable, such as when a foal would be threatened. Nonetheless, because of their physiology horses are also suited to a number of work and entertainment-related tasks. Humans domesticated horses thousands of years ago, and they have been used by humans ever since. Through selective breeding, some breeds of horses have been bred to be quite docile, particularly certain large draft horses. On the other hand, most light horse riding breeds were developed for speed, agility, alertness, and endurance; building on natural qualities that extended from their wild ancestors. Horses' instincts can be used to human advantage to create a bond between human and horse. These techniques vary, but are part of the art of horse training.
The "fight-or-flight" response Horses evolved from small mammals whose survival depended on their ability to flee from predators (for example: wolves, big cats, bears). This survival mechanism still exists in the modern domestic horse. Humans have removed many predators from the life of the domestic horse; however, its first instinct when frightened is to escape. If running is not possible, the horse resorts to biting, kicking, striking or rearing to protect itself. Many of the horse's natural behavior patterns, such as herd-formation and social facilitation of activities, are directly related to their being a prey species. The fight-or-flight response involves nervous impulses which result in hormone secretions into the bloodstream. When a horse reacts to a threat, it may initially "freeze" in preparation to take flight. The fight-or-flight reaction begins in the amygdala, which triggers a neural response in the hypothalamus. The initial reaction is followed by activation of the pituitary gland and secretion of the hormone ACTH. The adrenal gland is activated almost simultaneously and releases the neurotransmitters epinephrine (adrenaline) and norepinephrine (noradrenaline). The release of chemical messengers results in the production of the hormone cortisol, which increases blood pressure and blood sugar, and suppresses the immune system. Catecholamine hormones, such as epinephrine and norepinephrine, facilitate immediate physical reactions associated with a preparation for violent muscular action. The result is a rapid rise in blood pressure, resulting in an increased supply of oxygen and glucose for energy to the brain and skeletal muscles, the most vital organs the horse needs when fleeing from a perceived threat. However, the increased supply of oxygen and glucose to these areas is at the expense of "non-essential" flight organs, such as the skin and abdominal organs. Once the horse has removed itself from immediate danger, the body is returned to more "normal" conditions via the parasympathetic nervous system. This is triggered by the release of endorphins into the brain, and it effectively reverses the effects of noradrenaline – metabolic rate, blood pressure and heart rate all decrease and the increased oxygen and glucose being supplied to the muscles and brain are returned to normal. This is also known as the "rest and digest" state.
As herd animals Horses are highly social herd animals that prefer to live in a group. An older theory of hierarchy in herd of horses is the "linear dominance hierarchy".
Newer research shows that there is no "pecking order" in horse herds. Free ranging, wild horses are mostly communicating via positive reinforcement and less via punishment. Horses are able to form companionship attachments not only to their own species, but with other animals as well, most notably humans. In fact, many domesticated horses will become anxious, flighty, and hard to manage if they are isolated. Horses kept in near-complete isolation, particularly in a closed stable where they cannot see other animals, may require a stable companion such as a cat, goat, or even a small pony or donkey, to provide company and reduce stress. When anxiety over separation occurs while a horse is being handled by a human, the horse is described as "herd-bound". However, through proper training, horses learn to be comfortable away from other horses, often because they learn to trust a human handler. Horses are able to trust a human handler. Since it is not possible to form interspecies herds, humans cannot be part of a horse herd hierarchy and therefore can never take the place of "lead-mares" or "lead-stallions".
Social organization in the wild Feral and wild horse "herds" are usually made up of several separate, small "bands" which share a territory. Size may range from two to 25 individuals, mostly mares and their offspring, with one to five stallions. Bands are defined as a harem model. Each band is led by a dominant mare (sometimes called the "lead mare" or the "boss mare"). The composition of bands changes as young animals are driven out of their natal band and join other bands, or as stallions challenge each other for dominance. In bands, there is usually a single "herd" or "lead" stallion, though occasionally a few less-dominant males may remain on the fringes of the group. The reproductive success of the lead stallion is determined in part by his ability to prevent other males from mating with the mares of his harem. The stallion also exercises protective behavior, patrolling around the band, and taking the initiative when the band encounters a potential threat. The stability of the band is not affected by size, but tends to be more stable when there are subordinate stallions attached to the harem. In modern reintroduced populations of Przewalski's horse, the only remaining truly wild horse, family groups are formed by one adult stallion, one to three mares, and their common offspring that stay in the family group until they are no longer dependent, usually at two or three years old.
Hierarchical structure
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