Great Britain’s Michael Whitaker has been suspended for a doping incident affecting his show jumper Tackeray. The stallion tested positive for altrenogest, a hormone most commonly found in the product Regu-Mate, after an alleged feed bucket mix-up at the La Baule CSIO (France) in May.

The suspension will last four months, and Whitaker may return to the show ring on Oct. 25, due to his probationary status prior to the trial on Sept. 11.

The Fédération Equestre Internationale Tribunal found Whitaker had been “negligent” and was responsible for the mistake.

Whitaker’s groom, Cynthia Gurrie, who is no longer employed by Whitaker, claimed in a statement that she didn’t remember mixing the feeds incorrectly, but that it was the only explanation for the positive tests, according to the FEI report, which was released on Sept. 24. 

Because her argument did not provide any concrete factual evidence, the tribunal determined that it was insufficient to determine how the substance entered the horse’s body, and therefore the doping could not be proved accidental.

Regu-Mate, when present in the body of a male horse, is classified as a “Doping” Prohibited Substance under VR Article 1009 and the Equine Prohibited List. In mares, however, it is an acceptable drug as long as it is claimed on Medical Form 2, which reinforces that it is prohibited in stallions.

Whitaker, on several occasions, had made use of Medication Form 2 for his mares, and “he should have been well-aware that the substance was strictly prohibited in stallions,” according to the FEI report.