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".Heitor F, do Mar Oom M, Vicente L (2006) Social relationships in a herd of Sorraia horses Part I. Correlates of social dominance and contexts of aggression. Behav Process 73, 170–177. doi: http://doi.org/10.1016/j.beproc.2006.05.004Keiper R, Receveur H (1992) Social interactions of free-ranging Przewalski horses in semi-reserves in the Netherlands. Appl Anim Behav Sci 33, 303–318. doi: http://doi.org/10.1016/S0168-1591(05)80068-1Keiper RR (1988) Social interactions of the Przewalski horse (Equus przewalskii Poliakov, 1881) herd at the Munich Zoo. Appl Anim Behav Sci 21, 89–97. doi: http://doi.org/10.1016/0168-1591(88)90102-5 Vervaecke H, Stevens J, Vandemoortele H, Sigurjönsdöttir H, De Vries H (2007) Aggression and dominance in matched groups of subadult Icelandic horses (Equus caballus). J Ethol 25, 239–248. doi: http://doi.org/10.1007/s10164-006-0019-7 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
Horses have evolved to live in herds. As with many animals that live in large groups, establishment of a stable hierarchical system or "pecking order" is important to reduce aggression and increase group cohesion. This is often, but not always, a linear system. In non-linear hierarchies horse A may be dominant over horse B, who is dominant over horse C, yet horse C may be dominant over horse A. Dominance can depend on a variety of factors, including an individual's need for a particular resource at a given time. It can therefore be variable throughout the lifetime of the herd or individual animal. Some horses may be dominant over all resources and others may be submissive for all resources. This is not part of natural horse behavior. It is forced by humans forcing horses to live together in limited space with limited resources. So called "dominant horses" are often horses with dysfunctional social abilities - caused by human intervention in their early lives.
Once a dominance hierarchy is established, horses more often than not will travel in rank order.
Most young horses in the wild are allowed to stay with the herd until they reach sexual maturity, usually in their first or second year. Studies of wild herds have shown that the herd stallion will usually drive out both colts and fillies; this may be an instinct that prevents inbreeding. The fillies usually join another band soon afterward, and the colts driven out from several herds usually join in small "bachelor" groups until those who are able to establish dominance over an older stallion in another herd.
Role of the lead mare
Contrary to popular belief, the herd stallion is not the "ruler" of a harem of females, though he usually engages in herding and protective behavior. Rather, the horse that tends to lead a wild or feral herd is most commonly a dominant mare. The mare "guides the herd to food and water, controls the daily routine and movement of the herd, and ensures the general wellbeing of the herd."
A recent supplemental theory posits that there is "distributed leadership", and no single individual is a universal herd leader. A 2014 study of horses in Italy, described as "feral" by the researcher, observed that some herd movements may be initiated by any individual, although higher-ranked members are followed more often by other herd members.Krueger, K., Flauger, B., Farmer, K., & Hemelrijk, C. (2014). Movement initiation in groups of feral horses. Behavioural Process., 103, 91–101. viewed January 9, 20144, http://www.rug.nl/research/behavioural-ecology-and-self-organization/_pdf/kr_ea_bp14.pdf
Role of the stallion
Stallions tend to stay on the periphery of the herd where they fight off both predators and other males. When the herd travels, the stallion is usually at the rear and apparently drives straggling herd members forward, keeping the herd together. Mares and lower-ranked males do not usually engage in this herding behavior. During the mating season, stallions tend to act more aggressively to keep the mares within the herd, however, most of the time, the stallion is relaxed and spends much of his time "guarding" the herd by scent-marking manure piles and urination spots to communicate his dominance as herd stallion."The Natural Horse and Unnatural Behaviour." Reproduced with permission from the Proceedings of the BEVA Specialist Days on Behaviour and Nutrition. Ed. P.A.Harris et al. Pub. Equine Veterinary Journal Ltd. Website accessed June 22, 2007 at Effem-Equine.com
Ratio of stallions and mares
Domesticated stallions, with human management, often mate with ("cover") more mares in a year than is possible in the wild. Traditionally, thoroughbred stud farms limited stallions to breeding with between 40 and 60 mares a year. By breeding mares only at the peak of their estrous cycle, a few thoroughbred stallions have mated with over 200 mares per year. With use of artificial insemination, one stallion could potentially sire thousands of offspring annually, though in practice, economic considerations usually limit the number of foals produced.Bergstein, Stan. "We have the technology..." originally published in Daily Racing Form, March 12, 2002.
Domesticated stallion behavior