HILMAR, California (AP) _ Tom Silva's chickens pump out 1.4 million eggs a day, but his operation looks more like a prison than a farm.
To reach his hen houses, an intruder would have to scale 8-foot (2 1/2-meter) fences topped by razor wire, then sneak past surveillance cameras.
``Biosecurity'' is the buzzword du jour at chicken, turkey and egg operations across the United States. A bird flu pandemic sweeping through flocks in Southeast Asia and beyond has spurred American commercial farmers to tighten their defenses.
``This is certainly the biggest issue facing the industry today, no question about that,'' said Richard Lobb, spokesman for the National Chicken Council.
The stakes are especially high in California, where a $2.5 billion (euro2 billion) poultry industry ranks among the top 10 producers nationwide for chicken, turkey and egg output. State officials say migratory bird routes that stretch southward from the Bering Strait and down the West Coast could bring the disease by this summer.
A tradition of raising ``backyard chickens'' for eggs, meat, cockfighting and bird shows runs deep in some Asian and Hispanic subcultures here in the Central Valley. Industry executives and state officials say these backyard birds number in the millions, and they worry these birds out in the open could be exposed to sick migrating flocks.
Then they could pass the disease to their owners _ many of whom work at commercial poultry operations.
And there is painful precedent here. An outbreak of Exotic Newcastle disease killed more than 3.1 million birds, mostly poultry, in Southern California in 2002 and 2003.
Silva, vice president of the valley's J.S. West Milling Co., is as concerned about human carriers walking into his four facilities as he is about keeping sick birds out.
``If it gets into our industry, the only way to get it out is to euthanize complete complexes like this,'' he said during a tour of an egg-laying operation whose 1.5 million hens alone he valued at nearly $10 million (euro8 million).
The tour was brief, because no outsiders are allowed beyond the ``STOP: BIOSECURE AREA'' sign and razor wire _ not even the lab workers who collect blood samples once a month for disease testing. They too are on Silva's payroll.
Even the short tour provided striking evidence of the measures the poultry industry is taking to combat bird flu before it reaches America.
Today, all trucks entering and exiting Silva's complex get an automated bath of ammonia-based disinfectant. Incoming drivers are asked where they've been and whether they've been exposed to poultry.
Every employee enters the site through a ``dirty door'' into a trailer that serves as a changing room. They swap their street clothes for pre-washed boots, hats and coveralls, then enter the hen houses through a ``clean door.'' They reverse the process on the way out.
Various poultry companies even try to avoid each other on the road. They plot routes and stagger deliveries throughout the day, on the premise that the virus might jump from truck to truck.
The big rigs that rumble through the Central Valley most often bear the colorful logo of Foster Farms, which supplies dinner chickens primarily to consumers in the western states of California, Oregon and Washington.
Foster Farms is taking a different approach with its ``broiler''-raising farms. One of its facilities, the 120-acre (48-hectare) Gurr Ranch, is not ringed by razor wire or even fencing. The hen houses are padlocked, and outsiders are not welcome, but the real emphasis is on making the ranch as repulsive as possible to migrating birds.
The resulting landscape looks like a moon base, intentionally devoid of trees and ponds but colonized by 64 identical outbuildings that house nearly 1.3 million chickens.
Migrating birds are looking for food, water and shelter, said Charles Corsiglia, an avian veterinarian on the staff of Livingston, California-based Foster Farms, the biggest poultry company in the West.
``If we make our farms so that they don't have those things as they're flying over, they say, 'You know, that looks like a really bad place to land, because there's nowhere for me to waddle around,''' Corsiglia said. ``'So I'm going to land at the dairy, or the canal.'''
Like the J.S. West Milling facility, the farm buildings are meant to be impenetrable by outside birds, though swallows flitted in and out of the eaves one recent morning. Corsiglia said these visitors can't get into the hen houses.
Every person must don disposable plastic boots before setting foot on the Gurr Ranch property. And truckers delivering feed are required to hose their rigs off with the same ammonia-based disinfectant used at J.S. West Milling.
It's all part of Corsiglia's three-part formula for biosecurity: isolating birds from disease, controlling people and equipment who come and go, and sanitizing everything.
``Animals that aren't exposed to disease don't get sick from those diseases,'' Corsiglia said. ``The logic is so simple, it's laughable.''
Exotic Newcastle hurt the industry, but forced it and the government to refine surveillance and response procedures, Corsiglia said.
U.S. Department of Agriculture officials believe farm workers who kept cockfighting roosters at home brought the disease to the egg farms where they worked. A quarantine on pet birds and commercial fowl in a 46,000-square-mile (117,760-square-kilometer) area spanning from Santa Barbara to San Diego cost federal and state agencies more than $151 million (euro123 million) but kept the disease contained to Southern California.
``That was kind of like a dry run,'' Corsiglia said. ``We never had it up here (in Northern California), which was actually very good because it showed the system really works.''
Exotic Newcastle lingered for years in California during an outbreak in the 1970s, but the 2002-2003 outbreak was eradicated in less than a year, said Steve Lyle, a spokesman for the California Department of Food and Agriculture.
Silva keeps a brown foam chick in the center console of his truck. It's made for squeezing _ a stress-buster.
He's not squeezing yet. Silva has invested $250,000 (euro203,000) since 2002 in biosecurity measures. But like many in the industry, he worries that a Chicken Little, sky-is-falling panic may be his business' worst enemy.
``It's not in the United States. It's not even close to the United States,'' he said of bird flu. Tens of thousands of Americans die each year from ``regular'' flu, Silva said. ``And we're worried about this bird flu?''