John Singleton and the Waterhouse family have arrived at Racing NSW's headquarters in Sydney for the inquiry into the performance of racehorse More Joyous.

The inquiry is shaping up to be a media circus, with over 50 reporters and photographers staking out the Druitt St lobby on Monday morning.

Horse trainer Gai Waterhouse slipped in early through an underground car park but husband Robbie and bookmaker son Tom were all smiles as they braved the flashbulbs, while media mogul Singleton and jockey Nash Rawiller were hot on their heels.

The inquiry was sparked after Singleton, More Joyous' owner, accused Tom Waterhouse of telling people the horse could not win the All Aged Stakes on April 27.

Gai Waterhouse's stable foreman Dave Meijer told the inquiry More Joyous was not eating as well as usual on the Wednesday before the All Aged Stakes.

Meijer, who has worked with More Joyous for five or six years, said he detected heat in her neck on the Thursday and applied ice that afternoon after physio Tom Simpson examined the mare.

He texted Gai Waterhouse at 2.16pm to say "she's in the yard and seems happier".

The following day he sent the trainer another text saying More Joyous was eating well again and exhibiting no soreness - "seems to be in a better mood".

Just after 4am on race day, he sent another message telling Waterhouse the horse "seems comfortable enough, not as bright as usual. Still looks great".

Waterhouse stable vet Leanne Begg then told the inquiry More Joyous' blood tests indicated she may have had an inflammation the day before the race.

After conducting a blood test on the Thursday night, Begg received a pathology report the following day which showed slightly elevated white blood cells.

However, the mare's temperature was normal, she said.

"They said she was eating well, but not off the ground," Ms Begg told the inquiry.

"To be honest, I wouldn't have noticed it."

Ms Begg gave More Joyous an injection of antibiotics around lunchtime on Friday.

She thought the mare would be alright to run in the All Aged Stakes, "but I thought she needed to be examined on the Saturday", she said.

Ms Begg gave More Joyous an injection of antibiotics around lunchtime on Friday.

She thought the mare would be alright to run in the All Aged Stakes, "but I thought she needed to be examined on the Saturday", she said.

Gai Waterhouse interjected during Ms Begg's evidence to clarify that she had indeed asked the vet whether More Joyous was right to run.

"I asked, `do you have a problem with her racing?'" Mrs Waterhouse said.

Ms Begg replied: "And I said 'not at this stage'."

Mrs Waterhouse said she had consulted with a number of people whether More Joyous was in racing condition.

"I consulted with my vet, with my rider and my trackwork rider," she told the inquiry.

"All agreed she was fine to race. I don't have a problem, I knew she had a slight issue, but I didn't think it would be a problem for her to race."

Veterinary consultant John Peatfield, who counts Singleton as a client, told the inquiry that upon examining More Joyous on the day of the All Aged Stakes he found she was fit to run.

Chief steward Ray Murrihy asked Dr Peatfield whether he was aware of a sensitivity in More Joyous and that she was reluctant to eat off the ground.

"It was worth some consideration, but as a result of my examination I didn't find a reason not to run the mare," Dr Peatfield replied.

The inquiry heard that he said at the time: "I can't guarantee she'll win, because that's not my job, but I can't see a reason not to run her."

More Joyous' treatment records did not show she had been dosed with two different antibiotics in the two days before her race.

Murrihy said the evidence suggested the mare was dosed with cartrophin on the Thursday and trimetrin the following day, but both were absent from treatment records.

"We never tried to hide anything," Mrs Waterhouse said, noting that Murrihy had been told the horse had been treated with antibiotics.

Murrihy replied: "I'm not suggesting you did, but it's important those records are accurate."

Mrs Waterhouse said she didn't think the issue would affect More Joyous' racing.

Tom Waterhouse reiterated to the inquiry that he never spoke to anyone about the mare's health, despite reports he had talked to rugby league great Andrew Johns about the horse before the race.

"I only saw (Johns) briefly before the race started and we didn't talk about More Joyous' fitness, health, or anything like that," he said.

Mrs Waterhouse said she never spoke to her son or her husband Robbie Waterhouse, also a bookie, about the mare.

"I'll happily swear on a Bible. The first time I made contact with my son was after the race when Mr Singleton screamed abuse at me," she said.

Murrihy told the inquiry he had accessed the telephone records of all major parties to the inquiry.

"They do provide a very interesting matrix," he said, to chuckles in the room.

Singleton told the inquiry that on the day of the All Aged Stakes he asked his racing manager Duncan Grimley whether there was any reason not to have a big bet.

"He said, 'yes, I wouldn't have a bet'," Singleton said.

When asked why not, he said Grimley replied: "I'm not saying (More Joyous) can't win, I expect it to win, but it looks like it has a problem with its neck, so it's not a betting day, let's just enjoy the day."

Singleton said that conversation was the first knowledge he had that anything was wrong, "but I hadn't seen the new facilities at Randwick so I decided to go anyway".

Murrihy said that in a live interview for TVN before the race, Singleton indicated he knew about the issue.

"You said, live before the race, 'absolutely no confidence because the trainer's son is saying to all my mates no chance, because it's got problems. I don't know what the problems are but I've gone off (it) a bit.'"

Murrihy said this indicated Singleton did in fact know about the problem.

"They told you not to back it, didn't they? That's not a glowing endorsement," he asked.

Singleton said he didn't report his concerns at the time because as far as he knew the comments were hearsay, and the horse had won before when "looking worse".

"I had a hearsay phone call, we didn't know what they were talking about. The horse had been cleared, (I thought) I was only going to cause a kerfuffle - in hindsight, how ridiculous," he said, to laughter.

"But I had massive concerns when I heard that (former jockey) Allan Robinson and Andrew Johns passed on information which Duncan Grimley said was a bit too close to the bone."