Irish trainer Luke Comer has been banned from racing for three years after 12 of his horses tested positive for banned anabolic steroids in an "unprecedented" scandal.
He was also fined a total of 85,000 euros and the 12 horses banned from running for a period of two years.
Comer has been ordered to pay 755,754 euros (£650,000) in costs.
He categorically denied that he or his staff were involved in doping the animals.
Comer admitted traces of banned steroids methandienone and methyltestosterone were found in hair samples taken from the horses at his stables in County Meath.
The case failed to establish how the drugs got into the horses' systems. Comer argued that hay fed to the horses may have been contaminated with drugs through pig slurry.
An Irish Horseracing Regulatory Board referrals committee, which dealt with the case, said the presence of banned substances in so many horses at one time was "quite unprecedented".
"It is fair to say that there was no direct evidence of deliberate doping in this case," it added.
"The board makes the case that there is no basis for concluding that there was environmental contamination."
The billionaire property mogul made history three years ago when he saddled He Knows No Fear to be the longest-priced winner in racing history at odds of 300-1.
He Knows No Fear was among the horses based at Comer's stables in County Meath that tested positive in November 2021.
The Irish St Leger, won by Eldar Eldarov at the Curragh last Sunday, was sponsored by the trainer's Comer Group International.