Under pressure to keep quiet about Dr Tom Brennan's involvement in his cobalt case, Sam Kavanagh became enraged when even his father believed the vet over him.

The outed Sydney trainer has again said he was pressured by the Flemington Equine Clinic vet and its practice manager Aaron Corby not to reveal Brennan supplied a substance called vitamin complex.

Kavanagh said Brennan and Corby "poisoned" his reputation with his father Mark Kavanagh and friend, trainer Danny O'Brien, in an attempt to deflect the blame in their three cobalt cases.

Both Kavanaghs and O'Brien had used the vitamin complex in drips given to horses that returned cobalt positives.

Giving evidence to his father and O'Brien's appeal against their cobalt disqualifications, Sam Kavanagh said Brennan and Corby initially maintained the vitamin complex was not behind the cobalt positives.

"I was put under significant pressure from Brennan and Corby and they had spent a lot of time obviously talking to my father and Mr O'Brien, pleading their innocence that it wasn't their product that had caused their problems," he said on Tuesday.

Kavanagh said Brennan and Corby poisoned his credibility with his father, with whom he had a strained relationship, and O'Brien, fracturing their friendship.

"It was a lot to do with the poisonous talk from Brennan and Corby trying to deflect the blame on to me and get themselves out of trouble," he told the Victorian Civil and Administrative Tribunal.

Kavanagh has again said Brennan and Corby tried to stop him naming the vet after a vitamin complex bottle taken from the Sydney trainer's kitchen was found to contain cobalt.

VCAT heard Kavanagh was told if he brought the clinic into the case he would directly implicate his father and O'Brien.

Kavanagh told NSW stewards in February 2015 that the bottle came from Brennan.

VCAT heard senior racing executive Matt Rudolph tried to influence Kavanagh to change his evidence during a meeting with the trainer and his father at a Sydney hotel in March 2015.

"Tom had convinced them that he hadn't supplied me with the bottle of vitamin complex that the stewards found," Kavanagh said.

"I was enraged because my father believed the vet over me."

Kavanagh said Rudolph, then the Australian Turf Club's executive general manager of racing and a friend of Brennan, was the one doing the persuading.

"Matt Rudolph tried to persuade me, and my father sat through that," Kavanagh said.

Corby has denied trying to cover up the clinic's involvement or that he and Brennan tried to pressure Kavanagh.

Once Kavanagh finishes his evidence on Wednesday, the heads of three labs involved in the cobalt testing are due to testify.