Racing NSW stewards have laid two charges against trainer Gai Waterhouse over the More Joyous affair.

Gai Waterhouse has been charged with "fail to report to the stewards any condition or occurrence that may affect the running of a horse in a race", chief steward Ray Murrihy told the inquiry in Sydney on Monday.

She has also been charged with "having failed to keep a record of treatments administered to a horse".

The trainer of the John Singleton-owned thoroughbred mare More Joyous has pleaded not guilty to both charges.

The charges against Waterhouse relate to a problem with More Joyous before the running of the All Aged Stakes on Saturday, April 27.

Even though the horse had some heat in her neck and was treated with an antibiotic, Waterhouse did not consider it was serious enough to tell stewards.

More Joyous owner John Singleton has also been charged with "conduct prejudicial to the image, or interests, or welfare of racing".

He pleaded guilty, saying comments he made to the media about the mare's performance in the All Aged Stakes were "inappropriate and regrettable".

But he said he hoped his 40 years in racing earned him some clemency.

"This is my first and hopefully my last stewards inquiry," Singleton said.

"I don't think anything I've done has been negative to racing (prior) to this inquiry.

He said the comments that led to his charge came after the "culmination of so many things on the one day".

"It was the straw that broke the camel's back as far as Gai and I were concerned, with the unintentional consequence of (sparking) this inquiry," he said.

Mr Murrihy said Singleton's behaviour amounted to "flying off and making accusations against your trainer of 15 or 20 years".

Singleton was fined a total of $15,000 for the two charges.

The chief steward said Singleton had been given a discounted penalty - down from $20,000.

"We take into account your guilty plea, your very good character in the racing industry, and we're also well aware of the many, many good things you do quite unannounced in the racing field," Mr Murrihy said.

But the public nature of Singleton's comments was an "antagonising" factor, he said.

"You must have been aware ... that saying those things on that stage was going to attract mass coverage," he said.

Singleton has been given two days to pay the fine.

The stewards also cleared bookmaker Tom Waterhouse of wrongdoing over allegations that he had been the source of a claim that More Joyous was too unwell to lower her head to feed ahead of the All Aged race.

"There's no evidence you received or passed on this information but you should be mindful of your public perception within the racing industry," Mr Murrihy told him.

He urged Mr Waterhouse to "isolate" his gambling business from his mother's activities as a leading trainer.

"You must not, in your advertising and your commentary, get too close to the bone," he said.

Speaking outside the inquiry, Mr Murrihy told reporters that racing officials would investigate allegations from brothel owner Eddie Hayson that two individuals had warned him More Joyous was unwell, and that one of these had a link to the Waterhouse stable.

Mr Hayson would not reveal the identity of his sources to the public inquiry but has agreed to do so in-camera.

"We've asked for those names, we'll follow those up," Mr Murrihy said.

"It would be of concern, as I understand it, certainly to the Waterhouse stable, if it came from staff.

"Those of us in racing know that information pretty quickly gets out of racing stables when there's a whole series, as there was here, of treatments (and) veterinary inspections, so we'll see what names are provided."

Singleton told reporters he was looking past the scandal of the past fortnight.

"That was yesterday, let's move on to tomorrow," he said.

"(I feel) good. It's over."

Asked whether he was concerned about the impact of the inquiry on his public standing, he said: "It's done nothing to my self-respect. Reputation is what other people think. You can tell me that, I can't."