The vet at the centre of a cobalt hearing into prominent Melbourne trainers Mark Kavanagh and Danny O'Brien has told an inquiry he is prepared to "cop my whack" for his involvement.

"As the primary care vet for these two trainers I have let them down," Dr Tom Brennan the Racing Appeals and Disciplinary Board.

"I was in a position of trust. I don't want to buck pass, I'll cop my whack."

Kavanagh and O'Brien have pleaded not guilty to charges of presenting horses to race with an elevated level of cobalt in their system.

But Brennan has pleaded guilty to all charges except the administration of cobalt to affect the performance of the horses.

The inquiry heard Brennan had made a mistake by providing IV drips containing cobalt to the horses trained by O'Brien and Kavanagh.

A partner in the Flemington Equine Clinic, Brennan told the second day of the hearing on Tuesday that the clinic's junior partner Dr Adam Matthews had sourced a bottle of vitamins from Canada that had been used in harness racing circles.

He was told the bottle contained concentrated B vitamins that aided recovery.

Brennan said there was innuendo about a trainer using IV vitamin drips and there was always pressure to access the latest veterinary products.

Brennan claimed Kavanagh had paid $3000 cash, which he passed on to Matthews, for three bottles of the substance and began using IV drips on September 27 last year.

The inquiry heard Kavanagh stopped the procedure a month later, saying he didn't see the benefit.

Brennan said O'Brien had made an electronic transfer of $3000 to his bank account which he then withdrew to pay Matthews.

O'Brien used the drips until late December.

The barrister representing Kavanagh and O'Brien earlier said Racing Victoria stewards as well as the trainers had been deceived by Brennan.

"We don't dispute that Brennan didn't know that the bottles contained cobalt, it was his conduct from (the) fourteenth of January," Damian Sheales QC said.

"He's been kryptonite to everyone."

Sheales said his clients had been consistent with their evidence to stewards throughout the investigation and did so under duress from Brennan.

The hearing will continue on Wednesday.