The Australian Cattle Dog (ACD), or simply Cattle Dog, is a breed of herding dog originally developed in Australia for droving cattle over long distances across rough terrain. The female Australian Cattle Dog measures approximately 43–48 centimetres (17–19 in) at the withers, and the male measures about 46–51 centimetres (18–20 in) at the withers. The dog should be longer than tall, that is, the length of the body from breast bone to buttocks is greater than the height at the withers, in a ratio of 10 to 9. An Australian Cattle Dog in good condition weighs around 18–25 kilograms (40–55 lb). Barking can be a sign of boredom or frustration, although research has shown that pet dogs increase their vocalisation when raised in a noisy environment. It responds well to familiar dogs, but when multiple dogs are present, establishing a pecking order can trigger aggression.