Less than 24 hours after a deadly infection of bird flu was confirmed at a turkey farm north of Des Moines, Iowa, Bud Wood packed about 3,500 rare baby chicks into boxes and put them in the back of a truck.

With the delicate birds just hours old, the president of Murray McMurray Hatchery hit the road around 1 a.m. on a Saturday to drive through the night to a friend's farm in Texas "just to have them in a safe place," he said.

Breeding chickens that are the valuable genetic source for egg-laying hens have gone into hiding as the outbreak of bird flu in poultry has developed into the worst animal-health emergency in U.S. history. Some have been relocated as far away as Brazil.

Wood's breeding stock includes chickens with genetic lines that date back to the early 1900s. Some of the breeds are so rare, he said, that if they were ever wiped out by the flu, "even to find them and build them back up to bigger numbers would take a long time."

So when turkeys about 13 kilometers (8 miles) from Wood's hatchery in Webster City, Iowa, were infected, he scrambled to relocate his most precious birds.

Wood made a "Noah's Ark" list of breeds he had to move to safety, including male and female White Cochins which look like snowballs with masses of downy feathers, and Anconas, a breed with lustrous black plumage that originated in Italy. He plans to keep the chickens in Texas through next spring while he monitors the virus in the Iowa epicenter.

Bird flu has killed more than 48 million chickens and turkeys since December, with most of the losses affecting egg-laying hens in Iowa, the top egg-producer in the United States. U.S. egg prices have soared as a result.

China halted imports of all U.S. poultry products this year because of the outbreak, while other global buyers have imposed more limited restrictions on trade.

FALL'S MIGRATING BIRDS A WORRY

Poultry breeders and hatcheries want to keep the flu away from their chickens, which are bred to produce hens for commercial operations and backyard coops.

Breeders and hatcheries are relocating parts of their flocks even though Iowa has had a month free of new infections in any poultry.

Warm weather has made it harder for the virus to survive outdoors, but the U.S. Department of Agriculture is worried that new cases will surge in the fall as wild birds that spread the disease begin migrating south.

Egg farmers whose hens have died because of the virus are making plans to fill their barns with new chickens in the coming months and will depend upon breeding stock to provide the replacement birds.

Hy-Line International, the world's biggest genetics company for egg-laying chickens, moved part of its breeding stock from Iowa to several other states within the last few months, said Tom Jorgensen, general counsel for the company. Before the outbreak, Hy-Line kept portions of its flock in just one other state as a precaution, he said.

The best genetic lines for egg quantity and quality can be used to breed hens year after year.

Jorgensen declined to reveal where Hy-Line had shipped its breeder birds, citing "security." The company, which is owned by the EW Group GmbH in Germany, is preparing to move more birds out of Iowa as a precaution, he said.

Hy-Line also shipped some of its breeding stock to Brazil to ensure the birds can be exported to overseas buyers who restrict exports from the United States because of the outbreak.

"I can tell you just other states," Jorgensen said about the U.S. destinations for the relocated birds. "We keep that part confidential."

Murray McMurray and Hy-Line said none of their flocks have been infected with the virus.