Tyson Foods Posts Lower Earnings  CHICAGO (Reuters) - Tyson Foods Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=TSN.N target=/stocks/quickinfo/fullquote"&gt;TSN.N&lt;/A&gt;, the largest  U.S. meat producer, on Monday said quarterly earnings dropped  by more than 50 percent in part to poor results in its beef  segment.