Respected trainer Ron Quinton will front an inquiry into elevated cobalt levels found in two of his horses.

Quinton will appear before Racing NSW stewards on Thursday over the high cobalt levels found in pre-race samples taken from Boss Lane and Imanui in August.

Since the Quinton case came to light, stewards have warned trainers about a brand of feed which contained higher cobalt levels than indicated on the packaging.

They also said trainers should be careful when ordering custom-made horse feeds, feed additives, and/or supplements as some manufacturers were not listing all the active constituents, and/or the concentration of all active constituents on the labels.