Images of Biddell, Kah and assistant foreman Ruby McIntyre with a plate of what appeared to be a white powder arranged in lines were circulated on social media last month.
In a hearing on Thursday, the Greyhound Racing Integrity Unit found Biddell guilty of conduct detrimental to the interests of greyhound racing and handed him a conditionally suspended one-month ban.
"Mr Biddell pleaded not guilty to the charge and made further submissions," the hearing report said.
"Having considered all available evidence, the charge was found proven and Mr Biddell formally found guilty."
Biddell must undergo an "agreed program" and provide proof of its completion within six months or the suspension of his registration will be enacted.
The stewards based their penalty on the trainer's good record and time in the industry, his personal circumstances and the need for a specific and general deterrence.
Kah and McIntyre are yet to face a tribunal after being charged by Racing Victoria for prejudicial conduct to the image, interests, integrity and/or welfare of racing.
McIntyre recorded and later shared images of Kah using an identification card to arrange the white powder into three lines during a gathering at Kah's home in June, Racing Victoria stewards allege.
After the photos were published, Kah said was she was focused on her recovery after a fall at Flemington in March left her in an induced coma for several days with bleeding to the brain.
"I won't be making any further comment," she tweeted on June 23.
Kah rode more than 100 metropolitan winners in the 2020/21 season to become the first woman to claim the Melbourne jockeys' premiership.
8°C