Milk will be tested for bird flu across the US in a bid to contain a virus spreading among farms.
A strand of the virus known as H5N1 – which has also been identified in birds in the UK – was detected in dairy cows in the US for the first time in March.
Since then, more than 700 herds have been infected in 15 states, compelling the government to order testing of raw or unpasteurised milk from 16 December.
Agriculture secretary Tom Vilsack said it will give farms “better confidence”, adding: “It will put us on a path to quickly controlling and stopping the virus’s spread nationwide.”
At least 58 people in the US have been infected with bird flu, mostly farm workers who became mildly ill, but the risk to people remains low.
Pasteurisation or heat treatment kills the virus in milk, making it safe to drink, but government officials continue to warn against drinking it raw.
Dairy farmers and processors across the country have been reluctant to test animals or milk for the virus, fearing economic repercussions.
But Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, has led calls made by vets, farmers, scientists and academics for nationwide milk testing.
“It’s another step in the right direction,” he said. “They’re coming around that we need a better handle on it.”
Under the government order, those who handle raw milk intended for pasteurisation must provide samples on request for testing.
It requires reporting of positive tests to the US Department of Agriculture and for herd owners to give basic information to help keep track of the disease.
In the UK, health authorities are preparing more than five million doses of a bird flu vaccine after securing a contract for their manufacture.
The jab is only intended for use if the same strand affecting cows in the US – H5N1 – were to spread among humans in the UK.
Last month, the Department for Environment, Food and Rural Affairs confirmed cases of bird flu at a poultry farm in Yorkshire.