Tyson Foods Inc.'s decision to stop buying cattle fed with a widely used supplement sent cattle-futures prices surging Thursday amid concern that the meatpacker's move could crimp already tight beef supplies.

Tyson, the biggest U.S. meat processor by sales, told cattle suppliers in a letter Wednesday that it would stop buying cattle given Merck & Co.'s Zilmax—which promotes weight gain—after receiving animals at some of its beef plants that had difficulty walking or were unable to move.

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