"U.S. drugmaker Merck & Co said on Friday it is suspending sales of its Zilmax animal feed additive in the United States and Canada following concerns about animals showing signs of distress after use of the product, which is given to cattle to increase their weight before slaughter."

"Zilmax has been the focus of attention in the livestock industry since Tyson Foods Inc announced last week it will no longer accept Zilmax-fed cattle for slaughter.

Chicago Mercantile Exchange cattle futures rose Friday on expectations that a cutback in Zilmax use could trim the supply of beef beginning this fall, although producers said they did not expect major changes."

Theopolis Waters and Tom Polansek report for Reuters August 16, 2013. [2]