Nancy Howell thought her daughter's appaloosa mare was acting strange, but she had no idea its life would soon be cut short.

"She was nervous being loaded into the trailer," Howell said. "We knew it was a problem, but we didn't know what it was. We thought she just wasn't being very cooperative."

Conquering her fear, Cotton put up with being loaded into the trailer and let Howell's daughter, Kacie, ride her in a barrel-riding demonstration.

Two days later, their vet examined the mare and delivered some stunning news: Cotton was totally blind. Fearful that she would injure herself after she broke through a fence, the family had her euthanized.

"She wasn't just our horse; she was our pet," Howell said. "We had her 14 years. It's hard for Kacie to even talk about it."

The Howells aren't alone. Appaloosas - Idaho's state horse and the storied mounts of the Nez Perce Tribe - are far more likely than other horses to suffer from an eye disease called equine recurrent uveitis. A study in New York state found that the odds of finding ERU in appaloosas were 8.3 times more likely than in all other breeds combined. And a University of Minnesota study concluded that appaloosas are eight times more likely to get ERU and four times more likely to go blind from it.

"It's not widely known among appaloosa owners that their horse is significantly more prone to develop uveitis," Montana animal sanctuary operator Steve Smith said. "There's some word of mouth, but it's mostly vets who see enough cases that they're aware anecdotally. And even vets aren't aware of the data behind what they're seeing. It's not just an anecdotal thing. It's real. It's a problem."

Smith and his wife, Alayne Marker, own the Rolling Dog Ranch Animal Sanctuary in Montana's Blackfoot Valley. They care for disabled dogs and cats, but specialize in blind horses. Of the 24 blind horses currently at Rolling Dog, 12 are appaloosas.

"We've had calls from all over the country and the world," Smith said. "We get a call about a blind appaloosa at least every couple of weeks."

"People call and say they have 10 appaloosas and two of them are blind," Marker added. "They say they'll never have another one. It's heartbreaking, because they're a wonderful, wonderful breed."

Prized for their strength, intelligence, smooth gait and calm dispositions, appaloosas are closely associated with North Idaho's Nez Perce Tribe. Meriwether Lewis, of the Lewis and Clark Expedition, praised the tribe's horses in his journal as being "lofty, elegantly formed, active and durable." The Appaloosa Horse Club, the breed's official registry, is headquartered in Moscow, and the distinctive, spotted horses are a common sight in North Idaho.

Rosa Yearout, a past president of the Nez Perce Appaloosa Horse Club, lost a prized appaloosa to uveitis about four years ago.

"Tall Chief used to go on the Chief Joseph Trail Ride with me," she said. "We kept him for quite a few years after he went blind, but then we had to put him down. It was hard because he was such a good horse. You see them go blind from time to time. There are all kinds of theories, but nobody really knows why."

Dr. Mark Rutherford, a University of Minnesota veterinary researcher studying a possible genetic link, says the cause is "still a mystery. A group in Germany is looking at a link to a bacterial infection, and I'm continuing my work, but nobody really knows why it's so prevalent in appaloosas. More research is needed. And if somebody came up with a theory that it was related to specific blood lines, we'd definitely want to know about that."

The Appaloosa Horse Club registry, Smith said, could be a valuable tool to study that.

"When you had horses who had it, you could use the registry to find the parents and offspring of those horses and see if they had it. That would map the incidence in blood lines and tell you whether it's random or just in certain blood lines. It could be invaluable for the research, and it wouldn't cost the club anything."

Appaloosa Horse Club CEO Steve Taylor says the club would consider research proposals to use the registry.

"If somebody had a solid study proposal put together, we would cooperate," he said.

Some say the club could do more to acknowledge the prevalence of ERU in the breed and help in finding a cure.

"We called the appaloosa club, and they said they didn't see it as a problem," Howell said. "This is our state horse, and they're doing almost nothing about it. People need to know that it's a problem, and the club should be helping with testing and research to keep it from happening down the road."

On their Web site, www.blindappaloosas.org, Smith and Marker add that they "have yet to hear of any initiative the (club) has launched to come to grips with this problem."

Taylor says he isn't convinced there's a need to do that.

"I'm not sure we have enough science to say there's a specific problem," he said. "It's an issue that needs to be studied. As far as the club taking an official position, we haven't."

Meanwhile, the breed appears to be losing favor with buyers.

The January issue of Equus, a magazine for horse owners, reported that in the decade ending in 2007, new appaloosa registrations fell 44 percent and transfers of ownership dropped 55 percent. Appaloosas had the worst numbers of the major breeds listed.

"We don't know the role blindness plays in that," Smith said.

"There are a lot of issues in why people choose one breed over another, but certainly we've heard from people whose appys have gone blind and they've said they'd never have another one. That's because it's such a heartbreaking experience to have a horse go blind."

Jerry Gage knows all about that. Gage, who has appaloosas and other horses on his ranch near Star, recently helped a young Boise girl take her blind appaloosa to be euthanized.

"She still can't talk about it," he said. "The horse trusts you, and you're leading it into a trailer to take it to be put to death. She was crying. We were all crying. It's tough."

Tim Woodward: 377-6409