Tomorrow's eight-race meeting at Ascot has been switched to Sunday because of the 40C heat forecast.
Racing and Wagering WA and Perth Racing will made the decision this morning after consultation with the Bureau of Meteorology.
The maximum temperature on Sunday is expected to be 35C, with PR to open its gates for free admission.
"The welfare of the animal is paramount in our sport," RWWA thoroughbreds racing manager David Hunter said.
"This plan addresses our concerns for not only the horses but also the welfare of the riders, trainers and associated staff."
The transfer of Ascot to Sunday will cause some disruption to riding ranks, with jockeys Shaun Meeres, Lucas Camilleri, Kyra Yuill and apprentices Jerry Noske, Ellie Cockram and Renee Forrest booked to ride at the Geraldton meeting the same day.
Meanwhile, WA's best sprinting mare Power Princess will be prepared by Caulfield trainer Mick Price for the rich Melbourne and Sydney summer-autumn carnivals.
Simon Miller trained the seven-year-old to win the Northam Sprint, Bolton Sprint, Roma Cup, Scahill Stakes and Prince Of Wales Stakes, while she also ran Group 1 placings in the Robert Sangster Stakes and Winterbottom Stakes.
Power Princess has won $841,200 from her 12 wins and nine placings in 30 starts.
"We are viewing the prep as her last," managing-owner Richard Farris said. "Simon is not going across to Melbourne with his younger horses until much later in the carnival.
"He spoke to Mick at the Magic Millions sale yesterday and gave him a few training tips on her."
Price said there were a "million options" open to Power Princess during the carnivals.
"The owners had picked out some races for her, but because she was out a bit longer she won't be ready for those races," Price said. "The boys at home said she has given them a good feel and is in good order.
"There are races like the Oakleigh Plate, weight-for-age, or the Newmarket Handicap."