Trainer Danny O'Brien has criticised Victoria's cobalt threshold and says he is hoping for a quick resolution to the case which has engulfed three leading Melbourne stables.

O'Brien, Peter Moody and Mark Kavanagh are the subject of an investigation into elevated levels of cobalt detected in swabs taken during the spring carnival.

The threshold was set at 200 micrograms per litre of urine in April last year.

O'Brien said he was frustrated at the way the controversy had been handled and insisted he, Moody and Kavanagh had done nothing wrong.

"It didn't take us long to work out what our routines are and what they were but we had to know what that meant in the context of this cobalt threshold," O'Brien told radio station SEN.

"And we've got a fair idea now what's happened.

"We've certainly done nothing different than we've done for a lot of years but it doesn't appear that this rule has been terribly well thought out or researched as to what normal treatments can have an effect on this threshold.

"There has been no cobalt administered in any way shape or form to any of our horses and we're expecting a quick resolution to this, hopefully in the next few days."

Chief steward Terry Bailey said he had heard O'Brien's criticism but would make no comment.

Bailey has said previously he would not put a timeframe on the investigations.

The chief steward has described the cobalt threshold as being "generous" while Racing Victoria's head veterinarian Dr Brian Stewart has said to get above the threshold would require a massive contamination or a pretty deliberate administration.

O'Brien said he has always given horses drips and certain supplements to horses to make sure they race at their best and recover quickly as well.

"There's nothing sinister that's gone on with these horses and the numbers on the tests certainly show that," he said.

He said the horses from his stable had tested marginally over the threshold.

"It appears to have happened over a period of time on a build up of their normal race day supplements and treatments," he said.