Father and son team Stephen and Michael McConville have been banned from racing for three years for horse doping.
Anseanachai Cliste was withdrawn from a race at the Cheltenham Festival on 17 March after being injected with a tonic which contained banned cobalt.
Trainer Stephen and owner and jockey Michael admitted doping charges at a British Horseracing Authority hearing.
The pair have apologised for the incident and said it was down to "lack of knowledge".
"This is no excuse for what happened at Cheltenham," they added in a statement.
Elevated levels of Cobalt are banned in racing as it is said to have a similar effect on horses to performance-enhancing EPO in humans.
Michael was originally banned for five years and Stephen for four, but the bans were reduced to three years after mitigation was taken into consideration by the disciplinary panel.
Cheltenham stewards ordered the horse, trained in County Armagh, Northern Ireland, to be withdrawn from the Foxhunter Chase on 17 March.
Anseanachai Cliste won the Ulster Grand National at Downpatrick nine days later, after which the Irish Turf Club says a drugs test came back negative.
At a hearing on Tuesday, the McConvilles faced charges of allowing or causing the administration, or conniving in the administration of prohibited substances, having such items in their possession on a racecourse, on a race day and attempting to obstruct the proper administration or control of racing specifically by deliberately misleading, or endeavouring to mislead stewards and/or a BHA employee.
Michael McConville also had to answer whether he failed to act in the interests of the horse's best health and welfare by administering substances, namely adrenal cortex, without veterinary consultation or advice.
Stephen McConville had to answer if he was complicit in assisting, aiding and/or engaging the responsible person (his son) for the horse in violations of the equine anti-doping rules.
Following the hearing, the pair released a statement accepting full responsibility and apologising for the incident.
"The horse was administered the tonic - Hemo 15 - which is a widely used nutritional supplement which, unknown to us, contained cobalt," it read.
"We now just wish to put this unfortunate matter behind us as it has caused a lot of stress to all members of our family."