Scientists at the U.S.D.A. lab in Ames who test for Mad Cow Disease will change their procedures after an animal examined last year was pronounced healthy, then found to have the brain-wasting ailment. A selection of animals that are slaughtered are given rapid-screening tests, and for a sample that gives suspicious results, the lab will do a second test. Mike Kelsey, the vice president of a cattle producers’ group says from now on, they’ll be even more thorough. He says any time U.S.D.A. gets an “inconclusive” result now from one of the rapid-screen tests, it’ll be routine to do both a IHC, Immuno-Histo Chemistry test, and a Western Blot test on that sample. Kelsey’s an official with Nebraska Cattlemen, the largest cattle producers’ group in the country. Former Nebraska governor and now U.S.D.A. Director Mike Johanns says notwithstanding the second case of the brain-wasting ailment found in an animal in this country, improved safeguards have brought the risk to the food supply “virtually down to nothing.” The experts say it’s not a case of one being better, another worse, he says. Johanns says “why even engage in the debate, let’s go ahead and use both.” He says the agency will develop protocols to do that. Johanns says D.N.A. tests are underway to determine the origin of the afflicted animal.