By Theopolis Waters and Tom Polansek

CHICAGO | Fri Aug 16, 2013 6:40pm EDT

(Reuters) – 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.

Reuters reported earlier this week that a second major meat packer, JBS USA, at a cattle industry conference had presented a video from a JBS plant showing cattle having difficulty walking after they were fed beta-agonist drugs, additives that speed weight gain in animals. [ID:nL2N0GD0RI] Zilmax is the leading commercial brand of beta-agonist.

In an interview with Reuters on Friday, Merck said no safety issues had been discovered in 30 studies since the product was introduced in the United States in 2007.

Continue Reading…http://www.reuters.com/article/2013/08/16/us-merck-zilmax-idUSBRE97F0S320130816