Trainer Ivan Furtado was fined £2,000 for running the wrong horses in two races at Southwell last month.
African Trader and Scribner Creek raced on January 14 in the incorrect races, despite new scanning procedures brought into place. Both horses were having their first runs for Furtado.
Scribner Creek ran in the 3.25pm race, for which African Trader had been declared, and came third.
African Trader ran in the 3.55pm race, which should have featured Scribner Creek, and dead-heated for seventh of 10 runners.
The latter was routinely tested and the British Horseracing Authority said the mistake showed up the following day through an audit process which reconciles raceday sampling information collected via a new IT-based collection system.
The BHA's view was that the horses became mixed up prior to arriving at the course and there was no deliberate attempt to conceal their identities.
But as it was the trainer's responsibility to ensure horses run in the correct race, a disciplinary panel fined Furtado £2,000 at a hearing on Thursday.
In July, Newmarket-based handler Charlie McBride sent out the 'wrong' horse to victory at Yarmouth.
McBride thought he had saddled 50-1 shot Mandarin Princess to win the opening two-year-old race at the Norfolk circuit, only for it to emerge it was year-older stablemate Millie's Kiss who passed the post in first place. He was fined £1,500.
Furtado, who is based near Doncaster, said: "It has been a costly mistake for a small training yard like ours, but we put our hand up that we made a mistake and we have to pay for it.
"It's not good that it happened, but we will introduce new measures in our yard to make sure it doesn't happen again.
"I believe it was a very fair hearing. The BHA was also very fair the way they conducted the investigation.
"Hopefully we can now put it behind us and concentrate on training horses."
