Limited data about the effects of cobalt on racehorses makes it difficult to rule out legal supplements producing unacceptable levels of the banned substance, a Queensland stewards' inquiry has been told.

Stewards resumed an inquiry on Thursday into a positive swab to cobalt returned from last year's Rockhampton Cup winner Vandalised.

Vandalised returned cobalt levels at 280 and 293 micrograms per litre, which is above the national threshold of 200mcg/L.

Trainer Jamie McConachy denied knowingly administering cobalt to Vandalised, saying it may have come from a legal supplement.

Dr Robert Kinobe, a James Cook University senior lecturer and pharmacologist, told Thursday's hearing while there was a lot of research into cobalt's effects on humans and some mammals, there was minimal information regarding horses.

He said there seemed to be only a handful of investigations on cobalt in horses which were held over a time frame he considered too short.

Dr Kinobe believes cobalt could be accumulated if administered intravenously over a period of 33 days.

He said it was likely absorbing the drug orally could increase cobalt levels as could having a horse in full training.

However, he said current research and scientific readings seemed to be inconclusive and there needed to be further research.

Dr Bruce Young, from the Racing Scientific Centre, said a lot of data had been collected over the past month which showed a low percentage of horses had cobalt readings around 200 micrograms per litre.

He said he understood about 50 per cent of trainers used supplements with a cobalt component but few horses were showing high readings.

Chief steward Allan Reardon adjourned the inquiry to a date to be fixed.

North Queensland trainer Glen Baker was recently disqualified for two years for a cobalt irregularity found in January's Doomben winner French Lesson.

His appeal is on July 17.