Glen Baker has become the first Queensland trainer charged by stewards after one of his horses returned a positive test to cobalt in excess of the national threshold.

Stewards opened an inquiry into the cobalt levels found in Baker's horse French Lesson after it won a benchmark race at Doomben on January 31.

After taking expert evidence and hearing from Baker, stewards charged the North Queensland trainer under Australian Racing Rule 178 for presenting a horse to race with a level of cobalt in its system exceeding the threshold of 200 micro grams per litre of urine.

Baker pleaded not guilty and asked for an adjournment so he could seek legal advice.

Chief steward Alan Reardon agreed to the postponement, provided Baker put in writing answers to submissions made by stewards before next Friday.

Outside the inquiry, Baker said he would consult barrister Matt Tutt who is handling another cobalt irregularity case involving Rockhampton trainer Jamie McConachy.

The McConachy matter has been adjourned until May 20 and he has not been charged.

During Wednesday's inquiry, the Racing Scientific Centre's Dr Bruce Young said two samples taken from French Lesson and tested in different laboratories returned readings well in excess of the Australia-wide cobalt threshold, which has been in place since January 1 this year.

One sample returned a reading of 790 micro grams per litre of urine and the other showed up at 846 micro grams per litre.

Professor Paul Mills of the University of Queensland said tests had shown that cobalt could help the production of red blood cells which could in turn aid performance.

He said the levels found in French Lesson would not naturally be present in a horse.

However, Baker told the inquiry he had no idea why the cobalt readings were so high and was adamant he had given French Lesson only legal supplements.

The Atherton trainer told stewards it was very hot when he left his North Queensland stables to take French Lesson to Brisbane and the horse lost condition during the trip.

He gave the horse what he believed were legal supplements to try to boost his red blood cells.

"In no way or form did I try to boost anything (illegally). I had no idea about how cobalt works and I was ignorant about it," Baker said.

Baker said he had seen Racing Queensland notices warning about the use of cobalt and threshold levels but did not fully understand them.