It is highly unlikely that a sedative will show up five weeks after it has been administered to a horse, according to an International Equestrian Federation (FEI) official.
Dr Frits Sluyter, head of the federation's veterinary department, told The Irish Timesyesterday that such a case, as described by Irish Olympic gold medallist Mr Cian O'Connor in relation to his horse Waterford Crystal, would be "unprecedented".
Similar results could only be envisaged if the actual date of administration was closer to competition or if the drug in question was for human use, according to Dr Sluyter. The use of drugs meant for humans is deemed a "serious infringement".
Dr Sluyter responded to Mr O'Connor's claims that only "minute" traces of a mild sedative were found in the samples from Waterford Crystal and the mare, ABC Landliebe, which tested positive at the Italian Nations Cup fixture in Rome last May.
However, under FEI regulations there is zero tolerance policy on sedatives, and therefore a concentration level would not usually be revealed.
Mr O'Connor's vet, Mr James Sheeran, last night said the substance administered to the horses was "not specifically a human drug".
Dr Sluyter said that would be "surprised" if an equine sedative had been administered to the horses five weeks before the competitions.
However, he said, no conclusions should be drawn at least until the B sample from Waterford Crystal has been tested. This process is expected to take at least three weeks.
Mr Sheeran, who treated both Waterford Crystal and ABC Landliebe, claimed only "traces" of a sedative were found in the samples from both horses.
"The levels given are so small", he said. Mr Sheeran blames the positive results on hyper-sensitive scanning techniques.
Neither the international governing body nor the national federation have made any statement about concentration levels in the samples.