Sadly, racing greyhounds are the "waste product" of the greyhound racing industry. Each year, thousands of young greyhounds who do not display potential to make money are disposed of at greyhound breeding and training farms. In addition, each week at tracks around the country, truckloads of failed or injured racers are sent to be killed at veterinary offices, animal shelters, research labs, and destinations unknown. Contrary to industry propaganda, the majority of greyhounds are not adopted out as pets each year. So long as large-scale dog racing exists, thousands of dogs will continue to be produced and destroyed.
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http://www.greyhounds.org/gpl/contents/proof.html