The vet at the centre of the Sam Kavanagh cobalt case has admitted he originally lied to Racing NSW stewards to protect his Melbourne clients.

Dr Tom Brennan of the Flemington Equine Clinic changed his evidence last month to confirm he was the source of Vitamin Complex, a substance later found to contain large amounts of cobalt.

By the time Brennan was questioned in the Sam Kavanagh affair, Melbourne trainers Danny O'Brien and Mark Kavanagh, the father of Sam, had been told by Racing Victoria stewards they had levels over the cobalt threshold of 200mcg per litre.

"My primary concern was for the Victorian trainers," Brennan said.

"I work closely with two trainers in Victoria and I felt I had a duty to protect them as best I could but I have caused them more trouble."

Brennan said he suspected the Vitamin Complex, which came from another vet, Dr Adam Matthews, was the source of the elevated cobalt levels.

"He was a junior partner and I trusted him that it had no cobalt in it," Brennan said.

He also admitted destroying records relating to express post dispatches of two bottles of Vitamin Complex.

Sam Kavanagh is facing a raft of charges over caffeine and elevated levels of cobalt found in Midsummer Sun after the horse won the Gosford Cup on January 9.

Kavanagh said he did not use the Vitamin Complex after the end of December but was put in touch with harness racing identity John Camilleri through Matthews.

Camilleri facilitated race day treatment of Midsummer Sun before the Gosford Cup.

Both Brennan and Flemington Equine Clinic practice manager Aaron Corby denied pressuring Sam Kavanagh to say the substance did not come from them.

Corby flew to Sydney on February 17, the day after Sam Kavanagh was told of the Midsummer Sun results.

Kavanagh said he was threatened with bankruptcy and defamation if he named the clinic.

Brennan has been charged in the NSW case and also in the cases involving O'Brien and Mark Kavanagh.

Camilleri is expected to answer charges on Wednesday.

Sam Kavanagh said he understood Camilleri to be a bloodstock agent who could send horses to his stable.