US Agriculture officials said yesterday that the cow diagnosed with the first US case of Mad Cow Disease was born in Canada. The American beef industry has been reeling since the December 23 announcement of the case of mad cow, the nation's first since its discovery in Great Britain in the mid-80s. The spector of Mad Cow has raised concerns in among US consumers about the safety of the beef supply. Dr. Jon Hallberg is medical director of the Primary Care Center at the University of Minnesota. He says that, although the disease is extremely rare in humans, it is 100-percent fatal.