Asthma: A chronic respiratory disease, often arising from allergies, that is characterized by sudden recurring attacks of labored breathing, chest constriction, and coughing.

Asymptomatic: Neither causing nor exhibiting symptoms of disease.

Australian Cattle Dog: Also known as the Queensland Heeler or Blue Heeler, a herding dog developed in Australia. A medium-sized dog characterized by much energy and an independent streak.

Australian Kelpie: A medium-sized Australian breed of sheep dog that comes in a variety of colors including red and black with white tips.

Australian Silky Terrier: See Silky Terrier

Australian Terrier: A small dog of a breed originally bred in Australia, having a coarse blackish coat with tan markings.

Auto-immune disease: A disease resulting from an immune reaction produced by an individual's white blood cells or antibodies acting on the body's own tissues or extracellular proteins.

Awn hairs: A part of the undercoat that is coarse and longer than the downy undercoat yet shorter than the primary guard coat.