The first race kicked off at 1pm with spectators cheering as Prioritise, ridden by Christopher Dell, came in just ahead of Crafty Lady.
Crowds milled in the band stand, while those seated beneath a sea of gazebos had front row seats for the action.
Mr Castles said the day was about family coming in and enjoying the races.
"I hope people will have a great day, and it's a great way for kids to experience racing at a young age."
For four generations of a Waipukurau family, enjoying the races had been a "family tradition for many years".
Dominic Cook, 8, and his brother Cameron, 4, had been brought to the races for years by their mother Emma, who herself had grown up watching the races.
The young boys were joined by their grandmother Heather and their great-grandmother.
Heather said: "It's a nice family way to start the new year. It's a great deal of fun, and apart from the Melbourne races it's the only time we bet."
Punters looking to escape the heat but not miss any excitement parked out inside the venue.
One of these, Bob Hannah, had been travelling from Palmerston North for the races since 1960.
A horse racer himself for more than 50 years, Mr Hannah said he really enjoyed the day, and racing.
"I'll never get out [racing]", Mr Hannah said, "I love racing the horses and the adrenaline."
A More FM Kids Go Racing section ensured younger attendees were not left out with a range of activities to get kids involved.
Events including a jandal toss, and a sack race on the track itself kept kids entertained in-between races.
These events tied into the traditional and quintessential Kiwi summer, said James Wigley senior events marketing manager for Hawke's Bay Racing.
