Merck & Co.'s animal health division said Friday it would temporarily suspend sales of its widely used feed additive Zilmax in the U.S. and Canada, while it investigates problems of animal lameness and immobility that some companies are associating with the drug.

Zilmax is a growth-promoting supplement that is fed to cattle in the final weeks before they're slaughtered for beef, and can add about 2%, or 24 to 33 pounds, to an animal's weight. Zilmax sales in the U.S. and Canada were $159 million in 2012.

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