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Federal wild-horse managers are suspending adoptions from their Herriman center and placing a quarantine on about 500 animals because of an equine-distemper outbreak.

Eleven horses have died — some on their own and some from euthanasia after being badly stricken — and two- or three-dozen more show signs of the upper-respiratory infection, said Gus Warr, head of the U.S. Bureau of Land Management's Utah wild-horse and burro program.

An outbreak happens just about every year, Warr said Tuesday, but this one is unusual in the number of animals it is affecting at one time. The BLM is separating the sick horses and working to disinfect their areas, he said. The agency plans to monitor all the horses for 30 to 45 days to see if the outbreak has run its course before resuming adoptions.

"We're just asking that the public be patient with us," he said, noting that some have probably already picked out horses. "We have a lot of horses we'd love to get adopted, but they'll have to wait a month or so."

State Veterinarian Bruce King said equine distemper is common, and he sees no reason for south-valley horse owners to be alarmed. Most domestic horses have exposure to the bacteria when they are young and develop antibodies from their mothers' milk, he said, but wild horses, which the BLM rounds up from its ranges, lack immunity.

"Here you've got horses on the desert, spread out, not much contact with each other, and you bring them in and congregate them together [where] there may have been some other horses that had this infection," King said. "You bring this [unexposed] population in, and they get infected."

The infection causes swelling of the lymph nodes under the jaw. King said it can debilitate some horses, forcing them to the ground. If they remain off their feet for hours, or overnight, they suffer muscle damage caused by their own weight, he said, and euthanasia becomes necessary.

King recommended the quarantine to the BLM. He said privately owned horses that don't have close contact shouldn't face a heightened threat.

Some horses are vaccinated against distemper, he said, although there is no requirement for it.

The wild horses are vaccinated before adoption, but about 200 have arrived from roundups during the past month and weren't yet immunized, Warr said.

That may have been a good thing for some of them, he said, because the vaccine doesn't become effective immediately. The stress of going through the chutes and receiving the vaccine could have contributed to more deaths among those infected.

The quarantine may also affect the next round of horses scheduled to arrive at Herriman. If the outbreak persists into December, Warr said, the BLM will send horses from a southern Utah roundup to another state instead.

Wild horses in Utah

The U.S. Bureau of Land Management has removed more than 14,000 wild horses and 500 burros from Utah's rangelands since government roundups began in 1975. More than 6,700 of the animals have been adopted locally.