LOUISBURG, Kansas (Reuters) -- The brown-and-white spotted calves appear happy and healthy as they amble through the tall grass of a northeastern Kansas field, never straying far from their mothers.
But back at the barn -- and in countless barns, feedlots, slaughterhouses and packing plants around the United States -- the health of cattle like these has become a hot-button issue.
Calls for widespread testing of the nation's beef supply have stretched from Tokyo to Arkansas City, Kansas, after the United States detected its first-ever case of "mad cow disease" in December.
The news sent shock waves through domestic markets and triggered an immediate halt to important international trade, including deals with Japan, which typically buys about $1.4 billion of U.S. beef annually.
