Poultry Producer's Stock Falls 23 Percent  NEW YORK (Reuters) - Poultry producer 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; on Tuesday said it is being hurt by lower wholesale  prices and higher grain costs in the current quarter, sparking  a 23 percent drop in its stock and pulling down shares of its  rivals.