The vet ran his hand along the horse’s neck and under the coarse drape of its mane. The gelding was an eight-year-old Friesian cross, one of a matched pair of cart horses their owner brought to Terlingua late last fall. He was deeply black, raven black, and he conveyed his nervousness by the mincing fidget-steps he took in the dust.

“Hello, horse,” Aaron Burbach, DVM, said. “You’re excitable.”

The thirty-six-year-old Burbach is Big Bend’s only mobile large-animal veterinarian. Although he has weighed bighorn, castrated alpacas, and roped llamas, his practice is typically limited to cattle and equines, with an occasional goat or 4-H hog. His truck is packed with drugs, tools, and water. Towed behind the vehicle is a folding stock that creates a chute to safely contain an animal for examination. Other Big Bend vets make ranch calls, but they keep regular office hours at stand-alone clinics with staff and boarding facilities. Burbach is mostly a solo operation. He has his truck, his inventory and equipment, his stock, and that’s it.

“I like horses, I like cattle,” he explained. “I want to be outside, not stuck in a clinic all day.”

Performing castrations, sewing lacerations, palpating cattle, and giving vaccinations are routine. Emergency C-sections on cattle are rare. Complicated surgeries are referred out. Burbach keeps images of interesting cases on his phone, like the horse that rammed a piece of wood through her nasal cavity and transformed, briefly, into a unicorn. He particularly enjoys dealing with the mechanics of horses’ feet and teeth. “You’re putting together a puzzle,” he said. “With a foot, I can trim, shoe, X-ray, and see the difference I made. With a colicking horse, I can hang fluids and treat, but I can’t see what’s going on internally.”

In Terlingua, Burbach checked the black horse’s respiration and heart. He secured the gelding inside the stock and administered a light sedative, then set out vaccinations and tools while the drug kicked in.

The horse’s owner watched. How’s the practice going, he asked.

“You get a good horse client, but they up and move or decide they’re not going to ranch anymore,” said Burbach. “But when ranches sell, sometimes the new folks hire me. And cow work is slowly building back up. It’s been interesting.”

The gelding’s eyelids drooped. Burbach and the owner conferred about vaccines: rabies, tetanus, encephalitis, and West Nile. After the shots, Burbach inserted a finger into the horse’s ear searching for ticks, then slid a hand into its mouth and felt for rough points along the teeth, caused from years of grinding roughage. Irregular edges can make sores inside the cheek that lead to infection or create pain for a horse ridden with a bit.

Burbach cleansed the mouth with a syringe of water and strapped a medieval-looking speculum on the horse’s head to hold its mouth open. He produced a cordless drill whose long-armed attachment held a paddle at the end. Into the horse’s mouth this went, and Burbach filed the teeth’s pointy edges.

The gelding’s eyes widened at the noise, which was louder than a human-scale dental drill. Dust plumes puffed from the horse’s mouth as Burbach filed, repositioned, and moved the tongue to the side to address problem spots. He paused and fished around again inside the mouth, feeling for smoothness.

“My favorite story is when a lady saw the dust flying out from the drill,” he said. “She asks me, ‘Is his mouth on fire?’ I wished I’d have said, ‘Yes, ma’am, but he’ll build up enough saliva to put it out.’ ”

He removed the speculum and swung open the gate. The tipsy black horse walked out and shook like a dog after a bath.

“Next!”

Burbach’s visits usually involve one owner’s animals, but sometimes neighbors pile on when he’s in the vicinity. In such cases, Burbach brings a young married couple, Jess and Colby Smith, as helpers. After the black horse came another black gelding, a buckskin in need of a tooth extraction, and a palomino with ringbone. Two sun-worn women shambled up with a couple of old horses. Burbach shared advice about feeding and dispatched Colby to trim the horses’ feet. A worried Thoroughbred arrived, accompanied by a fudge-colored donkey that was maneuvered directly in front of the stock to help keep the horse calm. The horse stared longingly at the donkey. The donkey napped.

Burbach is six three but seems taller wearing his hat. He sometimes booms when he talks, maybe a result of working outside. His horseshoe mustache extends a couple of inches below his chin, like a Civil War general’s, and he wears oxford shirts, tall-top boots, and a belt buckle with his initials fashioned into a brand. This punchy look retains no hint of Burbach’s suburban upbringing in The Woodlands.

“If I went to a high school reunion,” he says, “no one would recognize me.”

Burbach grew up a sports-playing kid with two siblings, an oil-and-gas-geologist dad, and a mom who took care of their world.

“I knew nothing about cows, horses, anything. The only thing I ever rode was a bike.”

Burbach studied mechanical engineering at Texas A&M. Late in his schooling, he drove to Montana on a lark and, despite an utter lack of experience, landed a summer-long cowboying gig. After graduation, he worked a job tending far-flung natural gas compression stations. One day at a Wyoming station, he watched cowboys trot past. He abruptly ditched the natural gas job and returned to Montana, where he regularly shadowed a large-animal vet, pestering him with so many questions that the vet let him assist. He became captivated with a copy of Up to My Armpits, Dr. Charlie Edwards’s memoir about his decades as a DVM in Marfa. Everything shifted. “I thought, if that’s being a vet, I can do that,” he said.

While at A&M vet school, Burbach met Chelsea Hall, a Marfa girl who grew up on a ranch south of town. He mentioned the memoir on their first date. Edwards was Chelsea’s family vet; she knew most of the places and people in the book. “I knew then I was going to marry this girl,” he said. Now six years into his practice, the Burbachs are raising a daughter, Whitley, five, and a son, Dal, one.

After a quick lunch in the Terlingua sunshine, Burbach drove to a nearby set of pens, where three large steers stood together: one white Longhorn, one brindle Longhorn, and one blue-speckled Longhorn-Watusi cross, a mountain-size animal with a wary demeanor and a pair of enormous, upright horns.

“His horn base is as big as your waist,” Colby told Burbach.

The steers’ owner arrived, and discussion ensued about trimming the brindle steer’s overlong hooves. The steer could not be run into the pens’ chute to be treated—his horns were too wide—so Burbach emerged from his truck with a dart gun straight from a James Bond movie. He carefully approached the steers. The blue steer pawed the ground and waggled his horns.

“The Watusi can be kind of ornery,” the owner called out.

The steers moved off. Burbach shot a tranquilizing dart into the brindle’s hip and retreated behind the fence. Minutes passed. The brindle swayed drunkenly but wouldn’t lie down. There came a second dart. The other steers assumed a protective stance, horns-out, in front of their woozy friend. Finally, he went down.

“That’s a prey animal for you,” said Burbach. “They don’t want to seem weak.”

The vet approached; the brindle suddenly leaped to its feet, and then all three steers pounded pell-mell from one adjoining pen to another. This went on for some time. Burbach and Colby shook out ropes and caught the brindle’s heel, but there was no containing the other steers, and despite the two darts, the brindle was too amped to continue. Mission terminated.

“Well, that’s how it goes!” the owner said.

The sun dropped behind the mountains on the drive home. Burbach thought out loud about his friends with straight jobs, guys with deadlines, offices, and traffic jams.

“My days are so different,” he said. “I did this today. Tomorrow I’m palpating six hundred cows. I take my family with me sometimes. I love what I do, and I’m still at the point where a good full day of work is a good day.”