Horse racing is one of the most popular and profitable sports, a £5 billion industry in the UK and Ireland followed by millions. Panorama reporter Darragh MacIntyre investigates what can happen to racehorses when their careers end. The industry says that racing is now safer than ever, that the number of deaths on the track is falling and that the animals are looked after in retirement. Panorama discovers that off the track, many horses suffer career-ending injuries, and rather than being rehabilitated or retrained for life outside the sport, race horses that have been owned and trained by some of the biggest names in the industry have been put down, some meeting grisly deaths.