It follows horse Flogas Sunset Cruise collapsing and dying after a practice routine at Cagnes-sur-Mer in France on October 10, 2016.

Thornton has been suspended for four months from the date of the decision, June 6, and has been fined CHF5,000 (£4,000/$5,300/€4,600) plus costs of the same amount.

In its findings, the FEI Tribunal determined that the athlete's behaviour "went way beyond what could be considered an acceptable conduct towards a horse".

It further concluded "with confidence" that the "horse has been whipped repeatedly, substantially and excessively and clearly more than the three times alleged by Mr Thornton".

The FEI stated in its testimony that "even if the horse had survived, a case of horse abuse would still have been opened by the FEI".

As the autopsy did not confirm the cause of death, the FEI Tribunal clarified that it was "not deciding on the potential responsibility of Mr Thornton for the tragic death of the horse".

FEI secretary general Sabrina Ibáñez felt the punishment was too lenient. 

"The FEI stood up for horse welfare by taking this case to the FEI Tribunal and given the severity of this incident I truly would have expected a much tougher sanction," she said.

"It was important to the FEI that the allegation of horse abuse was confirmed by the Tribunal.

"We had requested a two-year suspension, but the level of sanctions is at the discretion of the Tribunal and we respect its independence."

The decision can be appealed at the Court of Arbitration for Sport within 21 days from the date of notification, June 6.

The FEI opened a disciplinary case against Thornton in November.

It came after the launch of an investigation by the FEI, who claimed the welfare of horses was their "number one priority".

Horse Sport Ireland claimed to be "extremely concerned" by the incident, while the French Equestrian Federation opened their own investigation.

The Cagnes-sur-Mer Organising Committee filed a report with local police.

At the time Thornton admitted in a statement that the 10-year-old horse "felt very weird" and "suddenly collapsed".

He admitted to whipping him "once or twice" during the performance in order to encourage forward movement.

However, he strongly denied suggestions of wrongdoing and said he had been the victim of a "witch-hunt".

The 28-year-old added that he was "very sad and devastated about this tragic incident" and that "it is heart-breaking to see a horse die".