DEL MAR, Calif. – Doug O’Neill, the leading trainer this summer at Del Mar, has been cited for having his horse Argenta test for a high amount of total carbon dioxide (TCO2), commonly referred to as a milkshake, the California Horse Racing Board announced Tuesday. Argenta finished eighth in the sixth race on Aug. 25 at Del Mar. No hearing has yet been scheduled for O’Neill. Based on the level of TCO2 allegedly found in the test sample taken from Argenta, O’Neill could be facing a “minimum 30-day suspension,” Dr. Rick Arthur, the racing board’s equine medical director, said Tuesday afternoon. “To the best of my knowledge, no substance was given to this horse that would have raised her TCO2 level,” O’Neill said Tuesday afternoon. “Consequently, I’m working with CHRB investigators, trying to figure out what happened.” This is the second time O’Neill has been cited for a TCO2 infraction this year. In April, his horse Stephen Got Hope tested for a high amount of TCO2 at the Illinois Derby at Hawthorne. After a delay, O’Neill eventually served a 15-day suspension, from June 30 until July 15, during the end of the summer season at Hollywood Park. During that time, O’Neill’s owners joined him in solidarity, and he did not start any horses in the name of his assistant, Leandro Mora. O’Neill has won the Del Mar training title three times previously, in 2004, 2006, and 2007. John Sadler was the leader the last two summers.