Port Macquarie trainer John Sprague has been disqualified for 12 months after one of his horses returned an illegal cobalt reading.

Saint Denis returned a level above the allowable 100mcg/L in a pre-race sample taken at Tuncurry on October 29 last year when he ran third.

A level of 185 was detected in the first test while the B sample had a level of 177.

On Wednesday, Sprague appeared before Racing NSW stewards who disqualified him after finding him guilty.

Stewards said they took into account Sprague's unblemished record in 25 years of training and 40 years involvement in the industry.

Saint Denis was also disqualified from his placing in the race.

Cobalt is a naturally occurring trace element which can be detrimental to horses in high doses.