Before-the-Bell: Sanderson Farms Falls  NEW YORK (Reuters) - Shares of Sanderson Farms Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=SAFM.O target=/stocks/quickinfo/fullquote"&gt;SAFM.O&lt;/A&gt; sunk nearly 16 percent before the bell on Tuesday,  after the chicken producer's quarterly earnings fell short of  Wall Street estimates.