Pierro dominates Doncaster Mile betting but top trainer John O'Shea has declared Shoot Out a weighted certainty in Saturday's Randwick showpiece.

There has been healthy debate about the Doncaster handicaps this week with Pierro's trainer Gai Waterhouse expressing concerns over the three-year-old's 57kg impost.

O'Shea, who will saddle up $71 outsider Lightinthenite, believes Pierro has earned his weight but suspects Shoot Out has been leniently treated with 58kg.

"Shoot Out is the horse who has cheated the handicapper," O'Shea said.

O'Shea recalled his experience with Racing To Win who won the race as a three-year-old in 2006 carrying 51kg.

He missed the autumn and spring of 2007 and as a four-time Group One winner who had been sidelined for more than a year, was given 60.5kg for the 2008 Doncaster and didn't run.

"Racing To Win had won a Doncaster, an Epsom and a George Main and we nominated him for the Doncaster again and he got 60.5 kilos off a 51-kilo limit," O'Shea said.

"How does a horse like Shoot Out get 58 kilos when he's won five Group Ones?

"I think you put up a margin. Good luck to them."

Lightinthenite is one of eight horses in the field of 20 plus one emergency weighted on the 53kg limit.

His only start over the tough Randwick mile yielded a fourth in last year's Epsom Handicap.

That earned him a trip to Melbourne where he won the Group Three David Jones Cup (2000m) at Caulfield.

It is often said a horse needs to be able to run a strong 2000 metres to win a Doncaster and Lightinthenite falls into that category.

But O'Shea says the compressed weight scale disadvantages his horse.

"He's got a wonderful profile for the race but he's poorly in at the weights," O'Shea said.

Pierro was at $2.20 on Thursday ahead of another three-year-old in the Bart Cummings-trained filly Norzita ($8).

There is great value outside that duo with in-form mare and Coolmore Classic winner Appearance at $11, Shoot Out at $14 and Streama at $19 the only other runners under 20-1.

Waterhouse said the favourite had enjoyed a trouble-free week.

"Pierro is fabulous," Waterhouse said.

"He's been shooting the breeze. He had a trot and canter (on Wednesday) and he galloped on Tuesday as his final major gallop before the weekend."

A win by Pierro on Saturday will result in Waterhouse superseding her famous father TJ Smith as the most successful Doncaster trainer.

The pair currently shares the record for number of winners with seven apiece.