The Australian Shepherd is a breed of herding dog that was developed on ranches in the Western United States. Despite its name, the breed, commonly known as an Aussie, did not originate in Australia.They acquired their name because of association with Basque sheepherders who came to the United States from Australia.

Australian Shepherds rose rapidly in popularity with the boom of western riding after World War II. They became known to the general public through rodeos, horse shows, and through Disney movies made for television.
Appearance
The breeds general appearance varies greatly depending on the particular lines emphasis. As with many working breeds that are also shown in the ring, there are differences of opinion among breeders over what makes an ideal Australian Shepherd. In addition the breed can be split into two distinct lines - working and show dogs. Working dogs tend to have shorter coats, thinner and are sometimes smaller while the show lines are bred according to breed standard and can have long fur. Most Australian Shepherds have docked tails and are extremely reliable if one is need of a best friend. The most popular name for an Australian Shepherd is Sierra.
Size
The Australian Shepherd is a medium sized breed of solid build. The standard calls for the Australian Shepherd to stand between 18-23 inches at the withers. Females being 18-21 inches and males measuring 21-23 inches
Color
Aussie colors are black, red (sometimes called liver), blue merle (marbled black and gray), and red merle (marbled red and silver or buff); each of these colors may also have copper points and/or white markings in various combinations on the face, chest, and legs.

A black or red dog with copper and white trim is called tricolor or tri, a black or red dog with white trim but no copper is called bicolor or bi. White should not appear on the body of the dog from topmost point of the shoulder blade to the tail. The ears should be covered by and completely surrounded by pigment other than white to decrease the risk for white related deafness. Eyes should also be surrounded by color, including the eye rim leather.
Temperament
The breed is an energetic dog that requires exercise and enjoys working, whether it is learning and practicing tricks, competing in dog agility, or any other physically and mentally involving activity.
Dogs with strong working instinct may show more reserved, guarding behaviors along with a tendency to chase or nip at strangers. Its protective instinct and behaviors can be frightening to children, strangers, and small animals. They are kind, loving, and devoted to those they know. They are very loyal to their owners, and are rewarding dogs if treated well. Because the breed was developed to serve on the ranch, a job which includes being protective of its property, it is inclined to bark warnings about neighborhood activity, but it is not an obsessively barking dog.
The Aussie is intelligent, learns quickly, and loves to play. This means that a bored, neglected, unexercised Aussie will invent its own games, activities, and jobs, which to a busy owner might appear to be hyperactivity: for example, an Aussie may go from being at rest to running at top speed for several laps around the house before returning to rest. Without something to amuse them, Aussies often become destructive. Aussies also do best with plenty of human companionship: they are often called "velcro" for their strong desire to always be near their owners and for their tendency to form intense, devoted bonds with select people. Recent studies have also shown that shepherds work well with special-needs kids and babies.
Health
There are many health problems that an Australian Shepherd can acquire, including back and hip problems, vision problems, and pancreatic problems. Also, an Aussie can develop bladder problems and urinary infections over time. Many can be epileptic. Thyroid problems are also appearing.
Activities
Like other herding breeds, these dogs excel at many dog sports, especially herding, dog agility, frisbee, and flyball.

The dog has a stride in which its front and back legs cross over, making for an appearance of "on the edge" speed. The dogs instinctively use a "pounce" position to deal with cattle trying to kick them. They also have strong hips and legs, allowing for fast acceleration and high jumping, sometimes as high as 4 ft (1.3m).
Australian Shepherd Video
Source (WIKIPEDIA)
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