MINNEAPOLIS — Poultry producers in the nation’s top turkey state are taking extra steps to protect their flocks after a devastating strain of bird flu was confirmed at two Minnesota farms in as many days last week, a disease that had already slammed the doors shut on some key export markets.

Most producers in the state’s $750 million industry were already strict about day-to-day biosecurity to try to ensure that no bird flu enters or leaves their barns, but they’re redoubling their efforts. The confirmation Saturday of the highly pathogenic H5N2 strain of avian influenza at a turkey farm in Stearns County, the third outbreak at a Minnesota farm this month, raised the stakes because it’s one of the top poultry producing counties in the state. The first two farms were relatively isolated.

Poultry farms are now scrubbing down truck tires with disinfectant on their way on and off farms, and some operators are using dedicated employees and equipment for each individual barn on their property to cut the chances of spreading the flu from building to building, said Steve Olson, executive director of both the Minnesota Turkey Growers Association and the Chicken and Egg Association of Minnesota.  If a barn needs service such as electrical work, he said, owners may wait until things settle down.

“Pins and needles,” is how Olson described farmers’ moods Monday. Saturday’s announcement followed Friday’s confirmation at a farm in Lac qui Parle County near the western border. The three outbreaks together killed tens of thousands of turkeys directly, and forced the farm owners to kill tens of thousands more to prevent any spread.

Nobody has figured out yet how the virus got into any of the affected barns, said Dr. Carol Cardona, a bird flu expert at the University of Minnesota.

Most U.S. turkeys and chickens spend their entire lives indoors to keep them away from waterfowl and other wild birds that could introduce diseases. Migratory ducks and geese don’t normally become sick from bird flu, but they’re a natural reservoir and can spread the viruses via their droppings. That’s why commercial farms typically require everyone entering barns to don protective coveralls and even make them shower on their way in and out.

Cardona said biosecurity doesn’t always work because it depends on everyone doing everything right all the time.

“Biosecurity is very dependent on human behavior. It’s not a perfect science,” Cardona said.

H5N2 also has been found this month in commercial and backyard flocks in Missouri, Kansas and Arkansas. Highly pathogenic strains also have turned up in several western states since late last year. While officials continue to stress that there have been no human cases of these strains in the U.S. and there’s no food safety danger to consumers, more than 40 countries including Mexico have restricted poultry imports. Some bans are limited to the affected states or counties, while China cut off all poultry shipments from the U.S.

Minnesota produces around 46 million turkeys each year worth about $750 million, and exported about 8 percent of its production, or $92 million worth, in 2013.

Mexico is by far the largest importer of U.S. turkey, said James Sumner, president of the Georgia-based USA Poultry and Egg Export Council. Mexico and some other major trading partners are starting to realize that there’s no danger from imported U.S. products because all infected flocks are immediately destroyed, he said. So Mexico is moving toward a regional approach to import restrictions and recently agreed to take raw chicken and turkey from affected states provided it’s destined for further processing, he said.

U.S. consumers likely will benefit from lower prices eventually because poultry that would have been exported will have to be sold instead on the domestic market, where excess supply puts downward pressure on prices, said Glynn Tonsor, an agricultural economist at Kansas State University. Chicken prices were already poised to fall because the broiler industry is ramping up production, he said.