Investigations into cases involving elevated levels of cobalt from three of the most prominent stables in Victorian racing are expected to take months.

Racing Victoria chief steward Terry Bailey says trying to find the source of the positives will be an exhaustive process.

Investigations will decide if charges are laid against trainers Peter Moody, Mark Kavanagh and Danny O'Brien - three of the biggest names in Australian racing.

"All I can go as far as to say is it will probably take months rather than weeks," Bailey told radio station RSN.

He said the three trainers had already been interviewed by Racing Victoria's compliance assurance team but he wouldn't put a timeframe on the investigation.

"I've learned not to try and guess. It will be obviously as quick as we can but when we're testing feed supplements and things, that all takes time," Bailey said.

The spate of positive swabs come out of the Victorian spring carnival, a showpiece time of the year for the racing industry.

Moody's stayer Lidari returned an elevated cobalt level after the Turnbull Stakes while the Mark Kavanagh-trained Magicool also returned a positive from the same meeting.

Three horses from the Danny O'Brien stable returned illegal levels during November.

Racing Victoria introduced a local rule in April last year, issuing a threshold for cobalt at 200 micrograms per litre of urine which Bailey said was "generous".

That figure was also adopted in a national rule introduced on January 1.

Racing Victoria chief veterinarian Dr Brian Stewart said research indicated the chances of a horse returning cobalt levels beyond the threshold on a normal feeding and supplement regime was in the "millions to one".

"To get above that threshold there has to be some either massive contamination of something or a pretty deliberate administration," he said.

Racing Victoria is also investigating elevated levels returned by three horses from the training partnership of Lee and Shannon Hope.

Moody, Kavanagh and O'Brien have all issued statements saying they were at a loss to explain the test results and that they would co-operate with racing authorities.