Antibodies for erythropoeitin, a blood-doping substance commonly known as EPO, were found in six racehorses at Sam Houston Race Park, the Dallas Morning News reported Feb. 18.EPO is a Class 2 substance under the guidelines of the Association of Racing Commissioners International. Because EPO and related substances are administered over time, they have been classified as a "prohibited practices" by several racing associations and jurisdictions.Currently, testing can only be done for EPO antibodies. The drug has led some in the racing industry to consider out-of-competition testing, which would not be done on race days. The proposal has raised some legal questions.The Morning News reported that the Texas Racing Commission would notify owners and trainers of the affected horses, but their names would not be made public at this time. Commission executive secretary Paula Flowerday said the tests were a "trial" to determine if blood-doping is a problem in Texas.