At least five winning racehorses have been disqualified by Texas racing officials after testing positive for crystal meth.  

Officials believe the horses may have been contaminated by handlers, with drug testers having also identified seven horse grooms with methamphetamine in the bloodstream.  

"The low level of methamphetamine in the sample, and its absence in serum, as well as other facts presented in the case file indicate that this positive test is a case of human contamination instead of intentional administration," the rulings read.

A spokesman for the Texas Racing Commission said that while there was no way to determine whether traces of crystal meth affected the horses during races, it was possible, and disqualification was therefore inevitable. 

Horse grooms who tested positive have been handed a mandatory 30-day suspension and forced to attend drug counselling sessions.