CHICAGO – After Tyson Foods Inc. announced last week it would cease processing animals fed with Zilmax, a widely used animal supplement produced by Merck & Co., both National Beef Packing Co. and JBS SA said on Aug. 12 they would not change their cattle-buying practices, according to The Wall Street Journal.  Cargill Inc. announced on Aug. 8, it would continue to accept cattle fed with this animal supplement.

On Aug. 7, Tyson sent a letter to cattle suppliers notifying them it would stop accepting cattle fed with Zilmax, which promotes weight gain, after receiving animals at some of its beef plants that had difficulty walking, or were unable to move. Tyson’s announcement ignited a rally in CME live-cattle futures because traders claimed the processor’s decision could result in tighter beef supplies.

"National Beef places a high priority on animal welfare with cattle in our facilities and we do not plan to change our cattle-procurement practices," National Beef said in an Aug. 12 statement.

Sáo Paulo, Brazil-based JBS SA said it has also noticed similar problems to what Tyson Foods cited, but it will continue its ongoing policy of "extensive monitoring" of animals at its facilities.

JBS spokesman Cameron Bruett said JBS hasn't been able to identify a cause. He added his company has a "heightened interest" in the matter, but would keep on accepting animals fed with the supplement.

Analysts said the ultimate impact of Tyson’s move on cattle and beef prices maybe limited unless the processors input put broader bans in place.