A random drug test on Mythilus carried out during the Games picked up traces of the prohibited substance Felbinac in the horse's system.

Courtney King-Dye, the horse’s rider claimed afterwards that Mythilus was contaminated while being treated for stress at the Hong Kong Jockey Club

But 22nd Sept, the International Equestrian Federation (FEI) announced that its disciplinary tribunal has disqualified Courtney. Her disqualification automatically loses America its fourth place in the Olympic team dressage competition.

In its ruling, the FEI disciplinary tribunal dismissed as "speculation" Courtney King-Dye's claims that her horse was contaminated while being treated at the Hong Kong Jockey Club.

But while it dismissed their claims as speculation, the FEI tribunal said it found the evidence of the rider and US dressage team vet "credible".

An FEI statement said: "The tribunal accepted [Courtney King-Dye] and US Equestrian Federation's arguments that they have done almost everything in their power to ensure no rule violation shall occur".

The disciplinary tribunal also weighed up the evidence that Felbinac, a non-steroidal anti-inflammatory drug (NSAID), has therapeutic applications and is considered as a "doping substance".

As a consequence, the FEI has imposed a one-month suspension on King-Dye. This has been in place since the Olympic Games, and ended yesterday (21 September). It has also fined her and imposed costs.

The FEI added that it took into consideration "the hardship already caused to Courtney King-Dye, including the fact that the US dressage team has already lost its 4th place at the Olympic Games".