The family was worried. Its 5-year-old doe was "acting like a boy." But whom do you call when your pet goat has a sexual identity crisis?

When she arrived on the scene, Dr. K.C. Fagan knew something wasn't right when the goat launched into a head butt, charging toward her legs. The gentle, slender-muzzled, Bambi-eyed goat had been transformed into an aggressive animal with a large snout and the pungent odor of a male—think funky cheese mingled with a hint of ammonia. The goat had also adopted the call of a buck, which sounds like an old man using his tongue to make farting noises. Not to mention her enthusiasm for humping all the other does in her lot.

Fagan had a mystery—and it was exhilarating.

There's not always a textbook for cases like this, and not every patient is that dramatic. But in her role as the "Goat Doctor of Portland"—the nickname Fagan has adopted as owner of Vineyard Veterinary Services—navigating her way through the unknowns is one of the things she enjoys most.

Growing up outside of Crane, Ore.—a tiny town nestled deep in the state's eastern reaches—Fagan always knew she'd end up working with animals. It was the kind of place where cows outnumbered people, all her classmates were ranch kids and cattle guards at the school entrance kept roaming bovines at bay. Fagan is now based in McMinnville, where there would have been plenty of livestock around to keep her busy.

But Fagan changed her focus after getting a call for a sick pet sheep. The owners, distraught that their companion of 15 years was so weak she couldn't lift her head, were simply grateful and relieved to finally find a doctor who would even examine the animal. The sheep was reacting badly to routine medication due to advanced age. After IV fluid, some vitamin B and plenty of pain killers, the sheep recovered and is still puttering around at the age of 16.

Fagan realized there had to be other cases like this one, and she was right. "Nigerian dwarf and pygmy goats are on the rise as the "it" pet. And here's why: because they rock," Fagan says. "They have super personalities, they're very curious, they're super-trainable."

She now takes calls originating everywhere from East Portland to Monmouth. Most cases, she says, are pedestrian: "Somebody's goat ate rhododendron leaves, so it's vomiting. That's me. Somebody's goat got bit by a spider and has a little abscess on its face. They call me. Somebody's goat has problems with urination or depression. That's all me."

But what was up with the identity-swapped goat? An ultrasound revealed the goat had a tumor that was producing testosterone. In all ways but the genitalia, her body had been telling her she was male, and the goat was referred for surgery.

Fagan faces a lot of situations, she says, in which a livestock veterinarian might simply have put the animal down: "When I pull out my text to say, 'What should I do in this situation?' and I flip to the page and it says 'Cull' or 'Ignore,' that's not an option for these animals. They're pets. Somebody loves them."