A Cox Plate winner, a leading trainer and a bottle of baby oil made for an intriguing aside at Randwick on Saturday.

Chris Waller was given a please-explain by Racing NSW chief steward Ray Murrihy after Adelaide was found to have had baby oil rubbed on its testicles before the $4 million Queen Elizabeth Stakes.

The premier trainer was surprised stewards were not familiar with the procedure, which he said was commonly used on colts and stallions to stop them pinching themselves.

"We do it to all our colts and we've done it ever since I started training," Waller said.

Murrihy took the case to Racing NSW's senior vet, Craig Suann, who concurred with Waller that using the oil as a lubricant was not uncommon.

"Some trainers think that, on the better-endowed colts and stallions, it can stop chafing of the testicles," Suann said.

"It's non-medicated so it wouldn't be considered a danger in terms of prohibited substances.

"But it is something we need to review."

Murrihy left the matter there and Waller said he respected the stewards' right to ask questions.

Adelaide finished eighth to Criterion in the Queen Elizabeth, his first and only run for the stable.

The trainer said the horse didn't handle the heavy ground and would now return to Coolmore's Irish trainer Aidan O'Brien.