Marty Wolfson has spent the past 35 years training thoroughbreds at Calder Race Course and remained dedicated to South Florida’s traditional “summer” race track.

Come Sunday, that will all change.

Wolfson will put his stable of horses on a van and ship them a few miles east to Gulfstream Park. For good.

In a brewing, head-to-head battle between Calder and Gulfstream for horses and bettors, Wolfson is switching sides.

“I hope Gulfstream squashes Calder,” Wolfson said.

Minutes later, the veteran trainer’s horse — Heiko — won the fifth race on the first day of Gulfstream’s summer meet. Monday marked the first time horses kicked up dirt in July at a track that’s been a Hallandale Beach fixture since 1939.

For decades, Calder had the summer and fall all to itself on the year-round racing calendar in South Florida. Gulfstream and, at one time, Hialeah divvied up the lucrative winter dates, when northern tourists arrive and feed dollars through the pari-mutuel windows.

Now, Gulfstream has decided it wants the summer dates, too, and has scheduled a racing meet that runs in direct competition — at least on Saturdays and Sundays — against Calder.

“Racing has radically changed,” said Bill White, who has won 15 training titles at Calder over the years. “It wasn’t that long ago you had to support racing with live [on-track] wagering dollars. And, in the summertime, there was no one here, so it made no sense for Gulfstream to run. Now, with the majority of racing coming via Internet and simulcasting, you can run in the summer and make sense of it.”

The result: a racing-dates war between two tracks that were once allies in the quest to eliminate historic Hialeah from the local racing landscape.

Gulfstream was the only track running live racing Monday. Calder has Friday to itself. But they will begin going head-to-head Saturday and Sunday, and the outcome is about as unpredictable as a full field of cheap claimers.

This much is certain: battle lines are being drawn.

Calder, which is owned by Churchill Downs, has told trainers stabled at its track that if they send horses to Gulfstream to race they’re not welcome back, a strategy the track employed successfully in its 1989 dates victory over Hialeah. The track is making exceptions on a “case-by-case basis.”

Gulfstream is trying to woo horsemen by offering higher purses, modifying its dirt track to withstand the heavy summer rains and preparing to expand its backside stabling area with a double-deck barn to accommodate up to 500 more horses.

Some Calder horses are already beginning to make the pilgrimage.

According to a Gulfstream spokesman Monday, 200 horses had already shipped from Calder during the previous 48 hours and another 300 are expected to make the move in the next 48.

Horses are the key. Without horses to fill its races, a track can’t survive.

Some bettors said they’re ready to make the transition, too, when the tracks begin running simultaneously and they have a choice of places to wager on horses.

“I would come here because of the facility itself,” said Ray Adler of Pembroke Pines, who has been going to the races for 40 years. “You’ve got a venue [there]. Over there [at Calder], it’s deadsville.”

Adler was among a few thousand fans to show up Monday at Gulfstream.