USDA holding press briefing as mad cow rumor roils market - Tue Apr 24, 2012 (Reuters) - The United States Department of Agriculture was holding a press conference on Tuesday as rumors that a case of mad cow disease was discovered in California sent live cattle futures tumbling. http://www.reuters.com/article/2012/04/24/us-usda-briefing-idUSBRE83N14L20120424