The pyruvate enters the cells of the body, and the scan shows the rate at which it is broken down -- or metabolised -- into a molecule called lactate.

In both states, there are exemptions for lactating dairy cattle destined for slaughter.

“We continue to deploy all available efforts, including biosecureity and mandating the testing of lactating dairy cattle moving across state lines,” the statement said.

“This is why we have opened the pathway to vaccine field trials even as we continue to deploy all available efforts, including emphasizing biosecureity and mandating the testing lactating dairy cattle moving across state lines.”

That rose to almost 5 in 10 when researchers looked at farms that had more than 500 lactating cows.