Explosive Miss won its 1200m race in Tauranga earlier this year and subsequently failed a random post-race drug test for caffeine - which is a prohibited substance in horse racing.
The horse's trainer, Clinton Isdale, told the Racing Integrity Board he had no idea how caffeine got into his horse's system - but said he drank roughly three cups of coffee a day and would then urinate in the same corner of the stables behind the horse stalls every morning.
Investigators for the board took soil samples from this area and confirmed the presence of caffeine.
"It is believed that the probable cause of Explosive Miss' positive has been via contamination by Mr Isdale urinating in the corner of the stables by the stalls," the board said in its decision.
As a consequence Isdale had to forfeit the $15,000 prize from his horse's win and was fined $2000.
Isdale had no previous charges for prohibited substances and told the board that he was truly sorry for what happened.
"I am a hard-working young trainer in the industry and have worked tirelessly to get to this position in racing.
"I'm truly sorry this happened and take full responsibility and have thoroughly improved my stable practices to ensure nothing like this happens again."
The board also noted in its decision that it had sent an advisory in 2018 after a spate of horses had been contaminated with prohibited substances through sawdust.
It recommended that sawdust in stables should be replaced regularly and that trainers stop urinating in their stalls.
A similar case in March last year resulted in a trainer also being fined $2000 after his horse tested positive for caffeine. It was found its trainer had also been urinating in the corner of its stall.
Caffeine is banned in the sport because it's purported to give the animals an edge.
The Equestrian Sports NZ website warns trainers to "be aware when drinking soft drinks around your horse, or eating snacks such as biscuits or chocolate bars as caffeine is a common positive test result."
