A horse trainer who was issued a hefty fine after stewards discovered the horse's blood contained nicotine during a race at Morphettville Race Course suspects a staff member vaping near the animal may have been the cause. 

Leon Macdonald, the co-trainer of the horse named Pimm's Party, said he had no idea how the blood sample provided after a Saturday race in July tested positive to nicotine and cotinine.

Both substances are prohibited under racing rules. 

The steward's report was released on November 7 and an inquiry into the positive blood result collected for Pimm's Party after it won Race 9 of the 1200-metre Zilzie Wines Handicap resulted in a $9,000 fine for Mr Macdonald.

According to the report, Mr Macdonald and his co-trainer Andrew Gluyas pleaded guilty to the charge after allowing the horse to compete with the presence of nicotine and cotinine in its blood. 

"In the circumstances, stewards imposed a fine of $12,000 , however having regard for mitigating factors, which included Mr Macdonald's and Mr Gluyas's guilty pleas, their cooperation and forthrightness during the process ... stewards reduced the penalty to a fine of $9000," the report stated. 

Mr Macdonald said injecting a horse with nicotine could be toxic which was why he was particularly confused by the positive sample. 

There are signs alerting staff and stable hands at Morphettville declaring vaping and smoking is not permitted near the horses.

Appealing the decision

Pimm's Party had to be disqualified from the race after the decision was made meaning it lost its first-place result. 

Mr Macdonald says he and Mr Gluyas intended on appealing the sentence. 

"We've appealed the penalty; I just think it's a ridiculous penalty.... we want to reduce it."