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Study: Controversial Feed Additive Zilmax Doesn't Affect Cattle Health

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Luke Runyon
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KUNC and Harvest Public Media

The feed additive Zilmax, which was pulled from the market after reports of lame and stressed cattle, does not harm an animal’s health, a university study found.

Zilmax, known generically as zilpaterol, was pulled from shelves in August 2013 and remains off the market, according to its manufacturer, Merck Animal Health.

On Tuesday, the University of Nebraska-Lincoln and USDA’s Agricultural Research Service released results of a study that showed no detrimental effects to cattle fed zilpaterol, said Ty Schmidt, a UNL animal scientist. Further, the drug seemed to help the animal handle stress by lowering body temperature and producing less cortisol, a stress hormone, he said.

The $500,000 study was paid for by UNL and ARS and undertaken before last summer’s controversy, Schmidt said. After the problems were made public, Merck asked the researchers to look at more issues and contributed about $80,000 for the work, he said.

The study contradicts many reports made last summer that cattle fed Zilmax were more heat stressed and showed up lame and with missing hooves just before they entered packing plants. The claims shook the cattle industry, triggering the four largest U.S. beef companies to place a temporary ban on buying animals that had been fed the additive.

Zilmax was used by roughly 80 percent of the industry to bulk up cattle just before slaughter, putting up to 30 extra pounds on an animal.

“A lot of the claims against Zilmax were anecdotal. They were not based upon scientific observation. They were not based upon any data,” Schmidt said. “We really wanted the scientific data to tell us: is Zilmax detrimental to animal well-being or is it not impacting well-being?”

Merck confirmed this week that Zilmax remains temporarily suspended in the U.S. and Canada.

“We continue to move forward on implementation of the various elements of the five-step plan,” said Kelly Goss, a Merck spokeswoman. “The process has been more time intensive than anticipated.”

The UNL findings add to the existing body of data that support Zilmax, she said.

“We support all research that provides additional data on and insights into the safety and efficacy profile of Zilmax,” Goss said.

Asked about the reports of stressed animals and a possible connection to Zilmax, Schmidt said he doesn’t believe there is any evidence to prove the claims.

“I do write off some of that,” he said. “If you can’t provide the data to back it up you’re really just making a guess or a shot in the dark to what actually caused it.”

Report of lost hooves can be attributed to poor nutrition, he said, and lameness could be blamed on the huge size of the animals.

Cattle set for slaughter are typically 1,500-1,700 pounds, when they used to be raised to about 1,200-1,300 pounds, he said. Zilmax can’t be blamed for all that weight, especially when it creates more muscle mass, not poundage, Schmidt said.

“We’re getting bigger and bigger animals. Their frames are not built for it. We need to go back to 1,200-1,300,” he said. “If we get back down to that size cattle I don’t think we’ll see this mobility issue again.”

Peggy Lowejoined Harvest Public Media in 2011, returning to the Midwest after 22 years as a journalist in Denver and Southern California. Most recently she was at The Orange County Register, where she was a multimedia producer and writer. In Denver she worked for The Associated Press, The Denver Post and the late, great Rocky Mountain News. She was on the Denver Post team that won the Pulitzer Prize for breaking news coverage of Columbine. Peggy was a Knight-Wallace Fellow at the University of Michigan in 2008-09. She is from O'Neill, the Irish Capital of Nebraska, and now lives in Kansas City. Based at KCUR, Peggy is the analyst for The Harvest Network and often reports for Harvest Public Media.
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