Animals play a central role in three major spectator sports which involve gambling: horse-racing, dog-racing and, to a lesser extent, cock-fighting. Because of the large amounts of money staked on the outcome of such events, the animals are subject to many abuses including drugging, biological manipulation and torture. For example, greyhounds, although gentle by nature, are often trained to become aggressive through systematic starvation. It has been estimated that 90% of greyhound trainers use live lures (such as rabbits) to stimulate the dogs to higher performance, resulting in some 100,000 small animals being torn apart annually. When they are no longer of value for racing they may be sold to research laboratories (an estimated 1,500 to 2,000 per year in Massachusetts alone). In the process of racing or fighting, many animals suffer severe injuries and have to be destroyed.