Trainer Doug O’Neill has been suspended by the California Horse Racing Board for 45 days because one of his horses tested positive for high levels of carbon dioxide in 2010.

O’Neill’s punishment won’t start before July 1, allowing him to continue training the horse I’ll Have Another for the Belmont Stakes on June 9.

I’ll Have Another won the Kentucky Derby and Preakness and is bidding to become horse racing’s first Triple Crown winner since Affirmed in 1978.

The racing board met in a closed session Thursday at Betfair Hollywood Park.

Lab tests showed that an O’Neill-trained horse, Argenta, tested positive for high carbon dioxide levels after a race at Del Mar in August 2010.

High levels of carbon dioxide are often considered evidence that a horse has been administered a “milkshake,” consisting in part of baking soda and sugar, to illegally boost its stamina.

The racing board in a statement said a hearing officer concluded that “milkshaking was not the cause” of the elevated carbon dioxide found in Argenta. However, the board said trainers are responsible for elevated carbon dioxide levels regardless of the cause.

O’Neill has repeatedly said he is innocent.


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California racing board suspends trainer Doug O'Neill