WICHITA, Kan. (AP) -- Tyson Foods told cattle feeders this week it will no longer buy animals fed a supplement that's designed to bulk them up before slaughter, citing experts who suggest the drug may be causing cattle to become lame.
The decision by the food giant has raised concerns from industry experts that less beef will be available, which would drive up consumer prices.
"There have been recent instances of cattle delivered for processing that have difficulty walking or are unable to move," Tyson told feeders in a letter. "We do not know the specific cause of these problems, but some animal health experts have suggested that the use of the feed supplement Zilmax, also known as zilpaterol, is one possible cause."
Tyson, one of the nation's largest beef processors, said it is still evaluating the problem, but as an interim measure will suspend purchases of Zilmax-fed cattle beginning Sept. 6.
"This is not a food safety issue," the Springdale, Ark.-based Tyson wrote. "It is about animal well-being and ensuring the proper treatment of livestock we depend on to operate."
Merck Animal Health, which makes Zilmax, said in an emailed statement that its product is safe for use in cattle. It said studies have found that cattle fed Zilmax have normal behavior and movement.
Merck, based in Summit, N.J., said it will work with Tyson to help identify other causes for the lameness.
"Again, we are confident that the totality of our data does not support Zilmax as being the cause of these experiences, and we remain confident in the safety of the product," Merck said.
Zilmax is one of two "beta-agonists" approved by the U.S. Food and Drug Administration. The additives -- fed to livestock 20 days before slaughter -- are mixed in with normal feeds and work at a cellular level to more efficiently convert the feed's nutrients into lean muscle instead of fat.
Zilmax has been available in the United States for cattle since 2007, and until now, all four of the nation's big beef producers have used it.
Tyson buys 26% of all cattle coming out of the nation's feedlots, CattleFax market analyst Duane Lenz said. He noted that the futures market rallied after the announcement Wednesday, but faded when other packers didn't immediately follow suit.
"Obviously less production, less beef is bullish for prices," Lenz said. "What that will mean for prices will ultimately rest with how many of the packers do or do not go along with what Tyson did."