Gwenda Johnstone has broken with her usual preparation in an attempt to get Precious Gem into winning form at Caulfield.

Johnstone has given the daughter of Econsul an extra week between runs as she heads to the Anniversary Vase (1400m) on Saturday.

Precious Gem generally races every two weeks but with an Adelaide target, the Group Two Queen Of The South Stakes (1600m) in two week, Johnstone has decided to give the mare more time following her last start fifth at Moonee Valley.

Johnstone said the mare had freshened up nicely but admitted Saturday's race is stronger than anticipated.

Precious Gem has been a model of consistency and followed a second placing to Futurity Stakes winner Suavito last October with victory over Queen of the Turf winner Amanpour over 1700m at Flemington on Melbourne Cup day.

Her form in the autumn has been strong, chasing home the highly regarded Noble Protector at her last two starts at Flemington and Moonee Valley.

However Johnstone said some of the mare's owners are disheartened that she hasn't been able to get back into winning form.

"I can't fault any of her runs," Johnstone said.

"She's had a bit of bad luck in a couple of them but some of the owners just need to remember that we're racing at the highest level against the good mares that are around at this time of the year.

"As we've said to most of the owners she's the only one we can bring down and race in these races."

Precious Gem is a $14 chance with last-start Mornington winner Under The Louvre the $2.90 favourite ahead of recent Leon and Troy Corstens acquisition Marianne at $5.

Group One winner Bel Sprinter, who carries topweight of 60kg and is lining-up for what may be his last start, is one of the outsiders as an $18 chance.

Caulfield track manager Jason Kerr is expecting up 5mm of rain.