PORTLAND — Police are looking to trade in their used models for newer ones.

They’re not talking police cruisers, though.

They’re talking horses.

By summer’s end, the department will have traded in three prospective police horses because of medical conditions or, in one case, bad temperament.

Now, police are looking to buy a pair of new horses that were bred for that purpose instead of using old hand-me-downs.

“We want to buy two young horses that will last and are bred to be police horses,” said Lisa Sweatt, one of the city’s mounted officers, as she sat atop Kookaburra, who will soon be Portland’s only equine crime-fighter.

The mounted patrols are a popular attraction in the city’s Old Port and serve as goodwill ambassadors for the city.

But age is a problem.

Spree was retired after 16 years on the force last year. And the replacements have had problems, as well.

Seventeen-year-old Akari, named after a salon that donated the $3,000 purchase price, was supposed to be Spree’s replacement, but the horse was retired because of a painful arthritic condition.

Two more horses tried out for the team.

One, however, was too high-strung to stay calm in heavy pedestrian traffic. The other also had an arthritic condition and will be retired at the end of the summer.

Charlene Quilty, one of the mounted officers, figures the city would benefit in the long run if it could buy young horses that could last for 10 years or more even though that could be expensive initially.

“A lot of people don’t know what horses cost,” Quilty said. “They think $3,000 is a lot of money, but that’s like buying a $500 car.”

Lt. Ted Ross, head of the department’s community affairs division, has contacted a breeding farm in Ontario that sells horses to the New York City and Boston police. He said $10,000 could buy two fresh young horses bred for police work and already somewhat trained.

As popular as the mounted units are, Police Chief Michael Chitwood said they will have to survive on donations or they will be discontinued. The veterinarian bills and other maintenance costs add up to more than $20,000 a year, above the expense of scheduling officers to care for and ride them, he said.

“Unless we come up with young horses and the money to pay for them, I’m going to disband the mounted unit,” he said.

Ron Ward, president of the board of directors for Portland’s Downtown District, says shutting down the mounted unit would be a loss for the city, and he expects businesses and individuals will step forward.