Kentucky regulators have drawn blood from all 20 entrants in Saturday's Derby in order to test for the illegal use of blood-doping agents such as erythropoietin and darbepoietin, Kentucky state steward John Veitch said on Thursday.
Results from the tests will not be available until after the Derby is run, but Veitch said the testing was significant because the entire Derby field had never before been subject to the blood-doping test.
Veitch said the tests are "another tool to ensure integrity."
Blood-doping agents, which increase the number of oxygen-carrying red-blood cells, are illegal in every racing jurisdiction.
According to Veitch, the blood sample from each Derby horse was divided in two, with one sample being sent to the Kentucky Horse Racing Authority's drug-testing laboratory at Iowa State University. If the tests indicate the possible presence of the drug, the other sample will be sent to the University of Pennsylvania for confirmation.
Blood-doping agents are so-called Class 1 drugs and the use of the drugs carry the strictest penalties in racing.