TOKYO (REUTERS) - Why the long face?

Simple. A pus-filled horse tooth has spelled the end of Victoria Max-Theurer's Olympic dressage dreams.

The Austrian's 11-year-old horse, Abegglen NRW, had been behaving strangely in training and, while the Olympic opening ceremony was under way on Friday (July 23) night, a health check revealed a tooth infection.

"This news is a heavy setback for Victoria. We hope that Abegglen will feel better soon and that Victoria will continue on her path," said Peter Mennel of the Austrian Olympic Committee.

Max-Theurer's teammates Christian Schumach and Florian Bacher will now compete only as individuals.

On Saturday and Sunday, the world's best riders and horses will compete for team and individual medals in dressage, also known as "horse ballet".

Germany's Isabell Werth, the most decorated Olympian of her sport, and Britain's dressage world number one Charlotte Dujardin, are hot medal contenders.