Faalcon, a 5-year-old chestnut gelding, won the Otago race by three-quarters of a length.
A swab and urine test afterwards showed traces of Ketoprofen.
It was later revealed that Dr Casey gave Faalcon a dose 55 per cent in excess of what was recommended for a horse of his weight, the tribunal heard.
Faalcon was disqualified, and his owners and trainers forfeited the $25,000 prize money and were fined $7500. Dr Casey is defending the allegations, and his lawyers are due to call expert witnesses as part of his defence when the hearing resumes today.
Yesterday, the council heard evidence from two of the horse's owners who said they were unaware of the dosage of Ketoprofen used before the race.
Faalcon was owned by eight people including Auckland lawyer John Carter and Whangarei trainer Kenny Rae who, with his wife Lisa, trained the horse.
In the lead-up to the Otago race on January 31, 2009, Mr Rae arranged for Faalcon to receive pre-race treatment from Dr Casey, a "reputable independent veterinarian" who had worked with Mr Rae for up to eight years.
Dr Casey had previously treated Faalcon with Ketoprofen because the horse suffered from arthritic knees, and it was not unusual for him to be treated prior to travelling.
The drug was used as an anti-inflammatory and pain killer.
The standard and accepted practice was to administer the drug 72 hours before a race so it was not in the horse's system during competition.
Evidence that Dr Casey had given Faalcon a dose in excess of what he should have was referred to the Veterinary Council and investigated by its Complaints Assessment Committee, which has brought the charges of misconduct.
Mr Rae yesterday told the hearing he had no indication Dr Casey had given Faalcon an incorrect dose of Ketoprofen. "There was nothing to alert me to a potential problem," Mr Rae said.
The hearing is set down for five days.
Ketoprofen
• A prohibited substance under the New Zealand Rules of Racing.
• Period of detection is 72 hours after it is administered at the recommended level.
• It is general practice that veterinarians administer a dose 96 hours before competition to add a 24-hour buffer to the 72 hour "detection time".
Source: Veterinary Council's Complaints Assessment Committee