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Zilmax Effects Disputed
Tuesday, July 22, 2014 10:57AM CDT

By Cheryl Anderson
DTN Staff Reporter

DAVENPORT, Neb. (DTN) -- While some in the beef industry fear a popular feed additive causes detrimental effects in cattle, a new study from the University of Nebraska found that Zilmax causes no detrimental effects.

Ty Schmidt, assistant professor of animal science at the University of Nebraska-Lincoln, examined the endocrinal changes in cattle fed Zilmax, a feed additive widely used to promote weight gain in cattle. Zilmax is typically mixed into cattle feed in the weeks prior to slaughter and can add approximately 2% to an animal's final weight by promoting the growth of lean muscle.

Zilmax is approved by the U.S. Food and Drug Administration for human consumption. It is classified as a beta-agonist, with its sole competitor being Optaflexx, both of which are widely used in the industry. Schmidt estimated as many as 70% of all U.S. cattle are fed a beta-agonist.

Zilmax was temporarily suspended by its manufacturer Merck & Co. Inc. in August 2013 after some of the largest beef processors in the U.S. expressed concerns that the additive may have adverse effects on cattle, including walking difficulties. The suspension came after Tyson Foods Inc., the nation's largest meat processor, announced it would no longer buy animals fed Zilmax after seeing animals with ambulatory problems at packing plants. National Beef Packing Co. and JBS SA announced they would not change their purchasing, but would monitor the situation closely.

DTN Livestock Analyst John Harrington said he believes Merck's difficulty in reintroducing Zilmax during a time of record high cattle and beef prices speaks volumes.

"Surely the market incentive to buy or sell a weight-enhancing product such as Zilmax could hardly be any greater than it is right now," he said. "That is, unless there are major concerns such as animal safety and consumer resistance that significantly compromise this extraordinary market promise."

Schmidt, the Nebraska animal scientist, told DTN his goal was to examine endocrinal changes to cattle fed Zilmax.

"Zilmax came out relatively quickly and there was no scientific data to back it up. The claims about animal well-being and changes in metabolic response had never been looked at," Schmidt said. His research was a joint venture with Jeff Carroll and Nicole Sanchez of the USDA Agriculture Agricultural Research Service,

The study involved 20 heifers, half receiving Zilmax, and half not. The research team collected blood, body temperature and video images during a 26-day period. On the last day of the trial and four days after the Zilmax supplementation was discontinued, the researchers exposed the animals to stresses to simulate being shipped to the packing plant. Animals were then slaughtered and their hearts, liver, lungs, kidneys and adrenal glands were studied.

The research did not directly evaluate lameness in cattle.

Heifers fed Zilmax had an increase in muscle mass, as expected.

A surprise was that during the simulated stress event, cattle fed Zilmax actually had decreased production of the stress hormone cortisol and decreased body temperature.

Schmidt found no significant changes in organs to indicate any detrimental effect to animal well-being. He pointed out that a pathology professor was brought in to do a complete histology, looking at 25 variables related to the heart. Only one animal had a slight difference in the right ventricle, although that could be due to a difference in the animal itself. Overall, Schmidt said the trial showed no heart damage related to Zilmax.

While the study involved only 20 heifers, Schmidt stressed that it should not be discounted as small.

"This was about as large scale as we could get," he said. Although we only used 20 animals, we took more than 2,000 blood samples and looked at more than 45 variables related to blood."

Merck announced plans to test Zilmax on about 250,000 cattle. If completed, it could be the most extensive study of any cattle feed additive. The study was delayed when the nation's largest meatpackers, including Cargill, and JBS, expressed concerns about marketing the beef from animals used in the study. Packers also fear repercussions from the public, both in the U.S. and export markets. Many countries, including China, Russia and the European Union, prohibit the use of Zilmax.

Even though Schmidt is confident in his results, he believes other trials need to be conducted. "It's better to base decisions on more than one study.

"There is no basis for fear about animal well-being and there are no food safety issues related to Zilmax," Schmidt said adamantly. "It is FDA approved and there has been no documentation ever of any food safety issues related to its use."

Cheryl Anderson can be reached at Cheryl.anderson@dtn.com


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