The Australian Turf Club has fired senior staff and shut down its mounted security operation in the wake of a horse mistreatment scandal.

The ATC's mounted security division takes in donated, retired racehorses and retrains them for life beyond the track. For seven years, the thoroughbreds have been used as horseback security patrols at race days, music festivals and doubled as props-for-hire at private events as well as modelling shoots for television shows including Australia's Next Top Model.

Pleaded guilty: Dennis Mitchell, the Australian Turf Club's general manager of security, risk and investigations.

But after Fairfax Media published explosive allegations that the horses were being mistreated and routinely sedated to fulfil gruelling routines, a Racing NSW inquiry hit two senior ATC employees with a string of charges under the Australian Rules of Racing. Last week, ATC mounted security co-ordinator Michelle Steele pleaded guilty to two counts of improper conduct. Along with the ATC's general manager of security, risk and investigations Dennis Mitchell, she also pleaded guilty to two charges of failing to provide veterinary treatment and a further count of conduct prejudicial to the image of racing. Fairfax Media understands their employment has been terminated.

ATC Chief Executive Darren Pearce said his organisation "acknowledges we must be an industry leader in everything we do, and maintain the very highest possible standards, especially around the care of our thoroughbreds".