Most authorities consider the greyhound to be the world’s fastest dog breed, with breeds such as Salukis, Afghan hounds, vizslas, border collies and whippets, falling shortly behind them in terms of top speed. Purposely bred for speed, greyhounds have been clocked at speeds of up to 45 mph. Nevertheless, the website Vetstreet reports that veterinarian Dr. Christine Zink suggests that many other lightweight, fast breeds are nearly as fast as greyhounds are, and reach speeds between 35 and 40 mph.