Trainer Mark Kavanagh and veterinary surgeon Tom Brennan each got a second mobile phone because they feared racing authorities were listening to their conversations, an inquiry has been told.

Brennan is a key figure in the inquiry into elevated cobalt levels in horses trained by Kavanagh and Danny O'Brien.

All three have been charged with Brennan giving evidence for a second day at the hearing before the Racing Appeals and Disciplinary board in Melbourne on Wednesday.

Brennan said he was talking to Kavanagh one day when he was told to ring him on the new number.

"If there's anything to do with cobalt I was to ring him on that phone," Brennan said.

"He was worried if someone was listening."

Brennan said he wasn't sure when Kavanagh got the second phone, believing it to be shortly after the trainer was notified on January 14 that Magicool had returned a cobalt level above the 200mcg per litre of urine threshold.

Brennan himself got a second phone in March.

"I only made one or two calls on it and that was it," Brennan said.

"We were jumping at shadows."

He said Adam Matthews, a junior partner in the Flemington Equine Clinic where Brennan was a partner, had supplied him with a bottle of Vitamin Complex that he was assured was free of cobalt and other prohibited substances.

He said there was no financial motivation and no personal motivation in taking the product which was later found to contain high levels of cobalt.

Brennan said as a racetrack vet he was always being asked to produce new vitamins that were within the rules.

"Every day I would walk into Kav's stable and he would say to me, 'if you don't find something, you are gone'", he said.

"I should have brushed it off."

Brennan, who is appealing a six-year disqualification imposed by Racing NSW stewards, said he had never walked away from a fight and that he was at the inquiry to tell the truth.

"I was deceived by Adam and that led me to deceive the trainers," he said.

"I'm extremely remorseful."

Brennan added Vitamin Complex to IV drips containing registered vitamin supplements.

Earlier the inquiry heard Brennan threw away the remains of a bottle of Vitamin Complex in a skip bin on the day he found out about the positive cobalt readings.

He said it was a mistake not to tell stewards of the Vitamin Complex but he was in a panic trying to protect himself, the Flemington Equine Clinic and the trainers.

"It started to snowball," he said.

"I was in a situation where it wasn't getting any better."

The hearing continues on Thursday.