After the final morning of submissions, Dr Tom Brennan's legal counsel gave an impassioned plea for leniency in relation to his cobalt offences.

Brennan's counsel, former AFL football operations manager Adrian Anderson, said he was hoping to establish special circumstances that might influence  sentencing for his client.

"Tom [Brennan] is truly and profoundly sorry. He knows he has let down the stewards, his profession and the racing industry, which has been his life. He did not know about cobalt and had nothing to gain," Anderson said.

He argued that Brennan's problems were caused by his once loyal friend Adam Matthews.

"He was taken for a ride by an untrustworthy person in Adam Matthews. He [Matthews] is an addicted gambler with shady connections," the barrister said. Judge Russell Lewis then described Matthews as a "serpent".

In a hearing lasting nearly three hours on Tuesday, much of the discussion related to penalties for the three parties, who were found guilty of cobalt charges in December.

O'Brien was found guilty of four charges of administering cobalt while Kavanagh was found guilty of one administration charge. Brennan was found guilty of five administration charges.

Damien Sheales, who was representing Kavanagh and O'Brien, spoke of the hardships that would confront his two clients.

Sheales pointed out that they had invested huge sums in their businesses. "The financial fallout will be spectacular, we're talking millions," Sheales said.

In contrast, Dr Cliff Pannam, QC, for Racing Victoria stewards, said that the professed lack of knowledge from all three parties about the make-up of the drips used was no defence.

"It's unreal to come to the conclusion they [O'Brien and Kavanagh] can be innocent because they say they did not know what was in the substance," Pannam said.

Cobalt cases in NSW led to huge penalties and, so far in Melbourne, trainers Lee and Shannon Hope have been disqualified for three and five years respectively after being found guilty of administering cobalt.