The routine hasn’t changed for six years. At the end of Canterbury Park’s racing season, Joel Zamzow takes A P Is Loose to his farm near Duluth, where the bay gelding spends three or four months hanging out and eating carrots.

Getting that extended break every year has kept A P Is Loose sound, healthy and happy — and his owner has reaped the rewards. The leading money-earner in Canterbury Park history will return to his summer job Saturday, kicking off his season in the $100,000 Mystic Lake Mile.

The race is part of Canterbury’s Northern Stars Racing Festival, which includes the $200,000 Mystic Lake Derby and the $100,000 Lady Canterbury.

A P Is Loose will face a stout field of 13 rivals on the turf course in his first race since last September. It’s a major challenge for the 8-year-old, but, Zamzow said, he shows no signs of slowing down.

“He’s got so much try and so much heart,” the Duluth resident said of his stable’s star, who has won $460,038 at Canterbury. “He’s stayed incredibly sound — he’s never missed a day of training — and he’s been so consistent year after year.

“I’ve never had a horse like him. He’s been a joy.”

Zamzow typically names his horses after his children, Mack and Hunter. Watching a highlight video of former Vikings running back Adrian Peterson inspired him to try something new.

He heard Canterbury race announcer Paul Allen, who does play-by-play for Vikings games, shout his signature line — “A.P. is loose!” — and decided it was “the perfect name” for a racehorse.

The easygoing gelding isn’t flashy or imposing. But he has become a popular presence at Canterbury, thanks to his name and his ability.

A P Is Loose has a remarkable record on the Canterbury turf, with 10 victories and 19 in-the-money finishes in 20 starts.

Overall, he has run 35 races in Shakopee, finishing in the money 29 times with 12 victories. All but $100 of his lifetime earnings have come at Canterbury.

He’s made enough money to keep him in carrots for many winters to come. As for his summers, Zamzow said the horse is proving as durable as his namesake.

“I never thought he’d still be running at age 8,” Zamzow said. “But he still loves what he’s doing. We have no plans to retire him until he tells us it’s time.’’