Things went wrong for lying Victorian trainers Danny O'Brien and Mark Kavanagh when NSW stewards caught Kavanagh's son with a bottle containing cobalt, a tribunal has heard.

Racing Victoria barrister Jeff Gleeson QC said O'Brien and Kavanagh had told many lies about their racehorses' extraordinarily high cobalt readings.

"To this day we'd be seeing and hearing the mock astonished shrug of the shoulders: 'I just can't understand what happened, we just feed them the same, we don't know'," Gleeson said.

But Gleeson said things went terribly wrong for the trainers when Kavanagh's son, trainer Sam Kavanagh, was caught with a bottle containing massive quantities of cobalt hidden in his kitchen cupboard in NSW.

He said vet Tom Brennan eventually cracked and admitted O'Brien and Mark Kavanagh paid him $3000 for three bottles labelled vitamin complex.

Gleeson said Kavanagh had told lies but knew, or at least suspected, his horse Magicool had received cobalt.

O'Brien continued to tell many lies over his four horses' elevated cobalt readings and to his horror had to admit paying for the bottles as there was a record of the bank transfer, Gleeson said on Monday.

Kavanagh denies paying Brennan for the bottles, the Victorian Civil and Administrative Tribunal heard.

O'Brien and Kavanagh are trying to have their respective four- and three-year disqualifications overturned by arguing the laboratories that did the cobalt testing were not properly accredited at the time.

Their barrister Damian Sheales said RV jumped the gun and created a mess by bringing in its cobalt threshold in April 2014 without waiting for the proper science to be determined.

He said Racing Victoria had misled the public about cobalt over the past 18 months when ultimately science had proved it to be "about absolutely nothing".

"What Racing Victoria has really done is fire an arrow and then walk up to the tree and draw a bullseye around where the arrow landed," he said.

Sheales said in April 2014, Australasian racing labs proposed a combined scientific study that would allow for the establishment of appropriate thresholds for arsenic and cobalt.

"Well too late in Victoria - the gun had been well and truly jumped on no science," Sheales said.

Sheales said the Perth-based ChemCentre and Hong Kong Jockey Club labs were not properly accredited to test for cobalt at the time of the O'Brien and Kanavagh tests.

He said Racing Victoria needed two certificates of analysis of the tests but charged and prosecuted the case with only one, misleading everyone including the Racing Appeals and Disciplinary Board.

Sheales said Brennan had always maintained he thought the bottles contained vitamin B12.

Brennan, who has also been outed by Racing NSW stewards, is no longer appealing his five-year ban in Victoria.