South Coast trainer Paul Murray has been found guilty of five cobalt offences relating to a stored sample taken from Alma's Fury four years ago.

Racing NSW stewards have rejected arguments by counsel for Murray that cobalt was not a prohibited substance at the time because there was no threshold in place.

The two tests on the sample taken after Alma's Fury ran second in the 2013 Doncaster Prelude showed levels of 890 and 940 micrograms per litre of urine.

A cobalt threshold of 200mcg/L was introduced in January 2015 and halved from September last year.

Stewards found a substance labelled "concentrated trace mineral" in a fridge during a stable inspection in June 2014.

They released their findings on Thursday but have not set a date for Murray's penalty hearing.