A leading NSW greyhound trainer has been banned from the sport for 15 years, after an investigation found he engaged in the "systematic" killing of underperforming dogs and dumped their bodies in mass graves near Cessnock.

Thomas Pullman was hit with the penalty after an investigation, led by former Racing NSW chief steward Ray Murrihy, found his actions had been of such a "disheartening and intolerable nature" they had created "a prejudice in the minds of the general public about greyhound racing generally".

The bones of 99 dogs were found in the mass grave. Credit:Jonathan Carroll

It means Mr Pullman, deemed substantially responsible for the deaths of at least 99 dogs at the Keinbah Trial Track, will be well into his 80s before the ban expires.

Four other people were handed disqualifications ranging between two and four years, after the Murrihy report found they knew "to varying degrees" about Mr Pullman's actions.