Racing Victoria’s Head of Integrity Services, Terry Bailey, has defended the national Cobalt threshold that resulted in three trainers being issued notification of elevated readings during the week, reports Racing Victoria.

It comes a day after Danny O’Brien, who had three runners return elevated readings,suggested the introduction of the rule was not 'terribly well thought-out or researched'.

In April last year Racing Victoria implemented a Cobalt threshold level of 200 micrograms per litre.

The threshold has since been adopted nationally, which Bailey said backed Racing Victoria’s stance.

“We were very keen, Racing Victoria, to implement a threshold back in April of last year and some eight months later the Australian Racing Board nationally saw fit to put the same rule in place,” Bailey told RSN’s Correct Weight.

“It certainly wasn’t done willy nilly and unfortunately the matter’s going to take time.

“There’s a number of vets around Australia that sit regularly to discuss these things and I suspect that they too didn’t come to this threshold without a great deal of thought into it.

“It’s the same threshold level that Harness Racing New South Wales put in place and is now in place nationally in both codes, harness and thoroughbreds.”

Bailey reiterated that the threshold was a generous one. Racing Victoria’s head of veterinary services, Dr Brian Stewart, said during the week that natural levels of Cobalt produced by horses were typically five to 10 micrograms per litre.

“Our view, and Harness Racing New South Wales’ view, was that 200 was a fair level to put in place to ensure that innocent people weren’t trapped,” Bailey said.

“At the end of the day, if you exceed the 200 there’s been some outside influence.”

The investigation into the elevated readings of O’Brien’s three runners, along with those returned by horses trained by Peter Moody and Mark Kavanagh, is ongoing and no charges have yet been laid.

WATCH: Danny O'Brien's initial response to the Cobalt investigation