The hostler stuck his fingers in the mouth of the police horse and peeled back its top lip, revealing a number tattooed across the pink flesh.

The tattoo divulged the gelding’s history as a former racehorse. The supple, well-groomed chestnut ran the tracks before it joined the force. Given the excitable nature of thoroughbreds, it takes an experienced handler to look one in the mouth.

“The racehorses are excited, jumping all the time,” Jaime Cedeno, a civilian hostler for the New York Police Department’s mounted unit, said as he lowered the horse’s lip and returned to forking wood shavings into the stalls. “They try to bite you.”

The mounted unit, one of the most coveted assignments in the department, requires a support staff. While the mounted officers patrol the streets and roam the crowds, civilian hostlers toil behind the scenes to feed and groom the horses, and farriers hammer out orthopedic horseshoes.

Mr. Cedeno, 42, of Brooklyn, knows all about racehorse temperament, having been kicked and bitten numerous times during his eight-year stint as a hostler with the Belmont Park Race Track at Elmont on Long Island. Mr. Cedeno has suffered less abuse in his four years as a police hostler. Five of the 19 mounts of Troop B, where he works, are former racehorses, and most of them adhere to the department’s no-bite policy, Mr. Cedeno said.

Mr. Cedeno plies his trade inside the spacious Chelsea barn at Pier 63, where the mounted unit has its headquarters, Troop B keeps its horses, and a barn cat named Murray roams the scrubbed floors. A white picket fence encloses an equestrian romping ground, where horses can exercise on even the coldest days of winter.

The horses work out daily, “and they’re as strong as oxen,” Sergeant Anthony Russo, 34, said.

“We have barns all over the city,” he said, “but this one is so wide open that we get cross-ventilation. It’s off the water and we have huge barn doors we can open and close.”

The police barn, sitting on the edge of the Hudson River, conveys a finicky kind of minute-to-minute cleanliness, as if every time a horse fouled its stall a man with a pitchfork was not far behind.

“I respect all horses,” Mr. Cedeno said, as he handpicked a gelding’s mane to keep it at the regulation four-fingers length. “I talk to them. I say, ‘Take it easy.’ I’m not scared of him. If you are scared, he knows. If you are nervous, he knows.”

But horse-whispering isn’t the only secret to keeping horses calm.

“No females in the group,” Sergeant Russo said. “If a female came in, they’d be going crazy.”

The police department has maintained a mounted unit since 1871, when saddle and carriage horses’ galloping amok on crowded streets became such a problem that the city founded a 15-horse unit to keep the peace. The unit gradually expanded until its 800-officer peak in 1904, when the popularity of the automobile eclipsed the horse, and the unit gradually waned to its current level of 100 horses. The headquarters at Pier 63 is one of five facilities that the mounted unit maintains, including the Remount facility at the Bronx, where officers and horses undergo training.

Mounted officers are used for crowd and traffic control at protests, strikes, concerts, and other large gatherings, and an officer in the saddle is equal to 10 on foot, according to the department. Officers aspiring to patrol on horseback must join a lengthy waiting list, and only candidates with an exceptional service record are considered. Once selected, the officer dons the distinctive spurred riding boots of the mounted unit, and fastens a braided black lanyard to his sidearm.

Mounted officers are a common sight around the country, though full-time city hostlers are hard to find, and farriers on a municipal payroll are even rarer.

“New York maintains civil-service positions for hostlers – they take care of the municipal horses – and may be the only city to do so since the Kaiser left Berlin,” Detective Edward Conlon wrote in his police memoir, “Blue Blood.”

New York pays its hostlers between $20,000 and $30,000 a year and pays its farriers between $40,000 and $50,000. The Dallas Police Department has two full-time hostlers for its 22-horse unit, but there are no hostlers at the Newark department, which has 18 horses, or the Los Angeles department, which has 30. The officers at those cities groom and feed the horses themselves. Unlike New York, the mounted units at Dallas, Newark, and Los Angeles outsource to farriers when their horses need shoeing.

Jerry Trapani, 58, a farrier from Queens, was self-employed for most of his 40-year career. Four years ago, he heard the police department needed a farrier so he took the exam. Mr. Trapani was tested for his experience, his temperament, the way he balanced the hooves in his hands, and his nail-driving expertise.

“It doesn’t hurt them at all,” Mr. Trapani said, referring to the nails.

In addition to shoeing the horses, Mr. Trapani checks them for physical ailments and injuries, which he then reports to a police lieutenant.

“When I was a kid, I wanted to be a veterinarian, but with my family situation I couldn’t afford it, so I had to go right into work and this was the next best thing,” Mr. Trapani said.

As a journeyman certified by the Kentucky-based American Farriers Association, Mr. Trapani said his training is equivalent to a master’s degree. The association’s executive director, Bryan Quinsey, 50, said that only 20% to 30% of farriers pass the training to become journeymen, which involves intensive physiological and anatomical study of horse legs, and the ability to craft orthopedic horseshoes. Making custom shoes to correct hoof pathologies is particularly important for urban horses, Mr. Quinsey said.

“It’s probably pretty strenuous what those horses go through, walking on the blacktop all day,” Mr. Quinsey said of the police animals. “That’s not like a horse that’s galloping through the pasture on the green grass.”

Journeymen can attend further training for therapeutic certification, which Mr. Quinsey compared to a doctorate because it requires a thesis on such topics as caudal heel pain and laminitis. Journeymen must work with a veterinarian for two years, documenting and photographing the treatment of a diseased hoof, before they attain therapeutic certification.

“It’s really tough,” Mr. Quinsey said, referring to the therapeutic certification. “There’s only three of them in the country.”

The vagaries of hoof pathology are beyond the understanding of most nonequestrians, and in social situations, when Mr. Trapani is asked what he does for a living, people are sometimes shocked at what they hear.

“A lot of the parties I go to are involved with horse people so they understand,” Mr. Trapani said. “When I’m not with horse people, a lot of times when I say I shoe horses, they think I said, ‘I shoot horses,’ and they say,’That’s terrible.’ “