(CNN) -- The ruler of Dubai's prestigious Godolphin operation in Britain is at the center of a major doping scandal after 11 of the stable's horses failed drugs tests.
Godolphin said Sheikh Mohammed bin Rashid Al Maktoum was "absolutely appalled" after regulator British Horseracing Authority (BHA) found anabolic steroids -- ethylestranol and stanozolol -- in 11 samples taken from 45 horses from its Newmarket stable in eastern England on April 9.
"I deeply regret what has happened," said Godolphin trainer Mahmood Al Zarooni, who now faces a BHA disciplinary inquiry, in a statement by Godolphin.
"I have made a catastrophic error. Because the horses involved were not racing at the time, I did not realize that what I was doing was in breach of the rules of racing.
"I can only apologize for the damage this will cause to Godolphin and to racing generally."
Anabolic steroids work on horses as they do on humans -- helping to build strength and muscle.
Stanozolol was still legal as recently as 2008, when Big Brown won the Kentucky Derby and the Preakness Stakes in the U.S. after having regular injections. His trainer's admission, and the subsequent outcry, led to the drug being widely banned.
However, it is still legal for out-of-competition use in Australia, such as helping to overcome injuries.
''Any horse that has been treated with anabolic steroids must be free of them by race day," Racing Victoria vet Dr Brian Stewart told the Sydney Morning Herald on Tuesday in reaction to Monday's Godolphin announcement.
Godolphin is one of the world's most successful stables, with more than 2,000 race wins since it was formed in 1992. It has been named Champion British Owner eight times, including last year, while Sheikh Mohammed and his family have also taken the title on multiple occasions going back to the 1980s.
Godolphin's Certify, unbeaten in four career outings and winner of the Shadwell Stud Fillies' Mile at Newmarket last September, was one of the horses to test positive and will not be allowed to take part in the 1,000 Guineas at Newmarket next month.
"Mahmood Al Zarooni has been advised of the analysts' findings and has been visited by an investigating officer," said Adam Brickell, Director of Integrity, Legal and Risk for the BHA.
Former Dubai Gold Cup winner Opinion Poll was another horse to test positive. Opinion Poll was ridden to victory in that race by Frankie Dettori, who worked for the Godolphin team for 18 years, but is now serving a six-month ban for doping.
"This is a dark day for Godolphin," said the British stable's racing manager Simon Crisford. "We are all shocked by what has happened. His Highness Sheikh Mohammed was absolutely appalled when he was told and this is completely unacceptable to him.
"We will await the outcome of the BHA inquiry before taking any further internal action.
"Sheikh Mohammed has instructed me to begin an urgent review of all of our procedures and controls. That is already underway and we will take advice from the BHA in completing it."
The BHA said the disciplinary hearing will take place at the "first available opportunity."
"Ethylestranol and stanozolol are anabolic steroids and therefore prohibited substances under British Rules of Racing, at any time -- either in training or racing," added Brickell, outlining the sport's doping rules on the BHA's website.
"The horses which have produced positive tests will also not be permitted to race with immediate effect and for an extended period of time.
"As part of the ongoing process, a decision will be made as to what period this suspension will be imposed for.
"The BHA understands the importance of this process being carried out as quickly as possible because of implications for betting markets."
Zarooni joined Godolphin in March 2010 and won the St. Leger, one of Britain's five classics, in his first season.
"News reports so far suggest this case is an aberration and is not indicative of wider use of anabolic steroids in British horse racing," said National Trainers' Federation chief executive Rupert Arnold.