Father and son training partners Lee and Shannon Hope have changed their pleas on six of their elevated cobalt charges.

The trainers on Friday night changed their pleas to guilty to charges relating to the administration, or causing to be administered, a prohibited substance to Windy Citi Bear, Best Suggestion and Choose last year.

The guilty pleas do not address any intention to affect the performance of the horses and relates to the administration of cobalt resulting in readings inadvertently or unintentionally above the threshold level of 200 micrograms per litre of urine.

The trainers have kept their not guilty pleas over the administration of cobalt for the purpose of affecting the performance of the horses in their respective races.

The Hope's hearing before the RAD Board commenced on October 15 and was adjourned on Tuesday.

It is due to resume on the day after the Melbourne Cup.

Trainers Danny O'Brien and Mark Kavanagh are due to front the RAD Board to have their elevated cobalt charges heard next month with Peter Moody's hearing in December.