A horse bought for $5000 by Neville Parnham to help his son Chris hone his riding skills at the beginning of his career could take her earnings past half a million dollars if successful in the Summoned Stakes at Sandown.

West Australian-based trainer Neville Parnham owns Vital Importance, along with his wife Carolyn and their daughter-in-law Jess, and trained the six-year-old mare until recently transferring her to Melbourne-based Henry Dwyer.

Chris Parnham rode Vital Importance to a first-up win for Dwyer at Sale in country Victoria last month and is aboard again in Saturday's Group Three Summoned Stakes.

He has been based in Victoria for the past couple of seasons and the 19-year-old has won more races on Vital Importance than he has on any other horse, with the victory at Sale his seventh from 24 rides on the mare with the other six in Perth.

When Neville Parnham bought Vital Importance as a yearling in 2012, Chris had yet to make his race riding debut and still hadn't when Vital Importance first hit the racetrack.

"She was a nice filly at the sale and I knew she wasn't attracting any bids," Parnham said.

"Young Chris might have been just an apprentice then and we decided we'd buy a couple of horses for him to ride, and not upset any owners, while he was learning and it might fast-track things for him.

"She's ended up being quite a good horse."

Another horse Parnham bought for $6000 that year was Magnus Missile who won five of her nine starts, with Chris aboard in all her wins, before an injury ended her racing career.

"They were two cheap horses who finished up being quite good kick-offs for Chris when he got going," Parnham said.

Vital Importance was twice placed at Listed level in Perth last summer and Neville Parnham then campaigned her in Melbourne where she was placed twice from four starts.

He decided to leave her in Victoria with Dwyer.

"With the vein of health she's in she should run up to her best," Dwyer said.