Above the Bit: Where the horse evades the riders aids by raising the head above the level of the rider's hands. This reduces the amount of control the rider has over the horse.
Action: The movement of the horse's legs.
Aged: A horse of 15 years of age or older. Prior to this age, experienced horsemen can estimate the age of a horse by examining the teeth.
Aging: The process of estimating the age of a horse by examining the appearance and development of the teeth.
Aids: Signals or cues by which the rider communicates his wishes to the horse. The "natural" aids include the voice, the legs, the hands and the weight. "Artifical" aids include the whip and spurs.
Airs Above the Ground: High school movements performed by highly trained horses, where either the front legs or all four legs are off the ground. Airs above the ground include the levade and the capriole.
Akhal-Teke: Ancient breed of horse originating in the Turkmenistan area, north of Iran and east of the Caspian Sea.
Albino: Term used to indicate lack of pigment. True albino horses have pink skin, white hair coat and pink eyes.
Amble: The slower form of the lateral pacing gait. (See Pacer)
Andalusian: Elegant breed of horse originating in the Iberian Peninsula. Known in Portugal as the Lusitano.
Anhidrosis: A condition in which the horse has a limited ability to sweat.
Anthelmintics: Name given to the various deworming medications used to control equine internal parasites.
Appaloosa: Breed of horse exhibiting one of a number of distinct coloration patterns of spots on the body. Develeped by the Nez Perce Indians and named for the River Palouse. Coloration patterns include leopard spot, blanket, snowflake, frost.
Appendix: A horse registered in the Appendix of the American Quarter Horse Registry. Quarter Horse/Thoroughbred cross.
Arabian: Ancient and graceful breed of horse, originating in the deserts of the Middle East and having a strong influence on many other breeds, including the Thoroughbred.
Ascarids: Equine internal parasite, also known as roundworms.
Artificial Aids: Mechanical means by which the rider conveys his wishes to the horse. Includes spurs and whip.
At Grass: A horse that has been turned out in a paddock or field.
Azoturia: Condition in which the horse experiences prolonged muscle contractions during exercise. Exercise-induced myositis. Also known as tying-up and Monday Morning sickness, because the condition often appears in fit horses following a period of rest.
Azteca Horse: Relatively new breed of horse, developed in Mexico by crossing Andalusians, Criollos and Quarter Horses.