Trainer Darren Smith will front stewards at the end of the month over doping charges involving the use of cobalt.

Smith has been charged after 17 of his horses tested positive to cobalt in race-day swabs taken between February 14 and May 20 last year.

Three of the horses - Braided, Idle Chat and Prize - twice returned positive results.

Cobalt was also detected in one of Smith's horses during an out-of-competition drug test in May.

During the three months, 11 Smith-trained winners tested positive to cobalt including Testarhythm.

An accomplished sprinter, Testarhythm returned an abnormality after winning the Listed Ortensia Stakes during the two-day Scone Cup carnival.

Smith has been charged under four separate Australian racing rules including AR175 which relates to the administration of a prohibited substance to a horse which is racing.

He has been stood down from training since a stewards' raid on his Newcastle stable in May.

The matter will be heard on February 24, almost three months after stewards opened their inquiry.

Cobalt occurs naturally in horses but in small concentrations.

In higher doses it is believed to improve a horse's stamina and performance.

Smith is the only thoroughbred trainer facing charges over the use of cobalt but three of Melbourne's top horsemen - Peter Moody, Mark Kavanagh and Danny O'Brien - are under investigation.

Horses from their stables returned positive race-day samples to cobalt during the Melbourne spring carnival.

NSW trainer Paul Murray has also had a horse return a positive test to the substance while three Queensland trainers are at the centre of a Racing Queensland investigation into positive swabs to cobalt.

Racing Victoria established a threshold of 200 micrograms of cobalt per litre of urine last April, a stance adopted Australia-wide on January 1 this year.