The US Department of Agriculture has quarantined a second cattle herd in Washington State.
The farm where BSE was discovered has been quarantined
The herd contains a calf born to the cow now confirmed to be America's first case of Mad Cow Disease, or BSE.
The US says it is using extra caution. The chief veterinarian officer says there is no evidence the disease can be passed from mother to calf.
Many countries have banned US beef imports after the first BSE case was diagnosed earlier this week.
Experts have predicted the news will cost the US cattle industry billions of dollars, as countries around the world rush to ban American beef imports.
In another setback for the industry, the government has admitted it still does not know where the infected cow was born or how it contracted the disease.
Both the industry and the government continue to insist that American beef remains safe.
The BSE crisis has affected exports of US beef
But the price of beef again dropped sharply on the commodities market.
In an effort to minimise damage, US officials are being sent to calm fears in Japan - just one of many countries to halt beef imports from America.
Other top importers of US that have banned US beef imports are Mexico and South Korea.
The European Union has banned most US beef for many years because of growth hormones.
The US dollar and Japanese stock markets have fallen since the suspected case was announced, while cattle futures slumped as far as markets allow.
BOVINE SPONGIFORM ENCEPHALOPATHY
First surfaced mid-1980s
Can pass to humans through infected beef products
Human form of disease called vCJD
vCJD has killed 137 people in the UK
Shares in McDonald's have fallen by about 5% on the New York Stock Exchange, although the burger giant said its supply chain was not linked to the suspected case.
BSE, or bovine spongiform encephalopathy, has been linked to new variant Creutzfeldt-Jakob Disease (vCJD), a human brain-wasting disease.
First diagnosed in Britain in 1986, BSE affected 178,000 British cattle and resulted in the eventual destruction of 3.7 million animals.
It cost British farming billions of pounds as countries around the world banned British beef.