Merck & Co. Inc. (NYSE:MRK) on Thursday denied that its animal growth enhancer Zilmax was responsible for cases of cattle with difficulty walking after Tyson Foods Inc., the largest U.S. meat processor, suspended purchases of heifers fed the drug.

In a letter sent to cattle feedlots, Tyson (NYSE:TSN) said it believed Zilmax, also known as zilpaterol, was “one possible cause” of cases of wobbly steers and urged them to remove Zilmax from feed rations.

The weight of cattle would likely decrease without the drug, resulting in less available beef and higher prices.

“We are surprised by Tyson’s letter,” said New Jersey-based Merck in a statement emailed to International Business Times. “We are confident that, based on all of the available data on Zilmax, the experience reported by Tyson is not attributable to Zilmax.”

“Indeed, Tyson itself points to the fact that there are other possible causes and that it does not know the specific cause of the issues it recently experienced,” the company added.

An analyst told IBTimes that Cargill Inc., a privately held agricultural giant, planned to keep using Zilmax. A spokeswoman for Cargill did not immediately respond to calls requesting confirmation.

But for Merck, the product is part of its lucrative, though relatively smaller, animal health unit, which brought in $3.5 billion of the company’s overall $44.5 billion in annual sales last year. Specific sales figures for Zilmax were not available.

“Cargill said they’re not getting rid of Zilmax,” Jon LeCroy, an analyst at MKM Partners, told IBTimes. “This doesn’t sound like it’s a wider issue.”

He said he expects the drug to remain in use.