The RSPCA has seized 21 sick or deceased greyhounds from a licensed and registered Marsden Park trainer.
Nine of the animals were found piled dead in a mass grave on the property.
Inspectors removed 12 sick and emaciated greyhounds from the property when they visited it on Tuesday, July 3. A further three sick greyhounds were taken during a subsequent visit on Monday, July 9.
The RSPCA said some of the 12 living greyhounds were starved while others had severe dental disease.
The RSPCA is investigating animal cruelty charges but none have been laid yet. The Greyhound Welfare Integrity Commission, launched on July 1, is also assisting.
The Hawkesbury Gazette has contacted the RSPCA and the Greyhound Welfare Integrity Commission and is awaiting reply.