The Lausanne-based CAS has deliberated on the matter after two American dressage athletes, Adrienne Lyle and Kaitlin Blythe, launched an appeal.

Their horses Horizon and Don Principe were both handed provisional two month bans on April 5 after samples collected at an event in Florida in February 2017 tested positive for banned substance ractopamine.

Both athletes were also given provisional suspensions before these were lifted by the FEI Tribunal.

The Tribunal did not clear the horses, however, but Lyle and Blythe's appeal allowed them to return to action while the CAS proceedings were ongoing.

CAS has now ruled that the two-month rule was created by the FEI "in pursuit of a legitimate aim" and has "a consensus of approval in the equine community".

It was also accepted that the policy promotes horse welfare and a level playing field and that it is "proportionate even in cases where it could be shown that any residual effect of the substances has disappeared before the end of the two-month period".

"We are delighted to have received such a clear endorsement of the FEI's policy on equine provisional suspensions from the Court of Arbitration for Sport," FEI secretary general Sabrina Ibáñez said. 

"Horse welfare is always top of the agenda for the FEI and the mandatory two-month provisional suspension of horses in banned substance cases is an important measure to ensure that the welfare of our equine athletes is not compromised."

Cases against Lyle and Blythe remain ongoing.