Last year's English St Leger hero Encke is among seven further horses formerly in the care of Mahmood Al Zarooni to test positive for anabolic steroids, the British Horseracing Authority has said.
The BHA undertook an extensive testing programme at the yard of the trainer following his eight-year suspension after he admitted adminstering banned drugs to 15 horses in his care.
The BHA testing has now uncovered another seven horses, including the Doncaster winner, who have returned positive results for the steroid stanozolol.
Testing at the other Godolphin yard of Saeed bin Suroor returned no positive results for banned substances, the BHA said.
Encke will now be banned from running for six months, meaning he cannot return to action until October 29.
The other six horses - Energizer, Genius Beast, Improvisation, Stamford, Steeler and Zip Top - will also be barred from racing until that date.
Al Zarooni has lodged an appeal against the severity of his initial suspension and the BHA has confirmed it will not take any further action until that matter is resolved, with the last week in June currently favoured as a potential hearing date.
Adam Brickell, director of integrity, legal and risk for the BHA, said: "We will not be taking any separate action in respect of these additional positive results whilst Mr Al Zarooni's appeal process is on-going.
"In the meantime, the latest findings from HFL Sport Science will form the subject of further interviews as part of the BHA's continuing investigation.
"From the outset, one of the aims of the investigation, in addition to trying to understand the environment within which such serious breaches came to be committed, has been to identify what measures are needed to ensure the yard operates in accordance with the Rules in future.
"The findings will be shared with Godolphin and will also assist the BHA with regard to the future licensing of the yard."
Paul Bittar, the BHA chief executive, said: "These test results endorse the swift action and measures taken by the BHA in this matter.
"Whatever the outcome of his appeal before the independent Appeal Board, the gravity and scale of the infringements warranted Mahmood Al Zarooni being removed from control of the yard as quickly as possible.
"We welcome the news that Saeed bin Suroor's horses tested negative and this clears the way for him to now take charge of Moulton Paddocks."