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UNL study takes some of the heat off of Merck's beta agonist Zilmax

Cattle and Beef Industry News
Jul 21, 2014

According to a recent study by the University of Nebraska-Lincoln (UNL) and the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS), beta agonists do not harm cattle, contrary to last year’s concerns brought up by industry partners.

The animal health debate was the core of Merck Animal Health’s reason for removing its feed additive, Zilmax. While Merck has been hoping to conduct its own large-scale study on Zilmax, setbacks—including lack of industry support—have delayed the progress. The feed additive, used to promote weight gain, was suspended in August of 2013 following the National Cattlemen’s Beef Association (NCBA) meetings, where several packers referenced situations that they believed may have been linked to Zilmax. Despite their concerns, at that point there were no scientific studies to pull a connection together.

The product was approved by the U.S. Food and Drug Administration and has been used on cattle to improve feed conversion, resulting in more beef from each animal harvested. Given a situation where the U.S. cattle herd is at its lowest number since 1952, maximizing the yield from each animal has become a priority, and according to the recent UNL study, the cattle feed additive Zilmax has no noticeable detrimental effect on cattle health or well-being.

During the 26-day study, scientists collected blood via catheters; body temperature; and video images from 20 heifers, which were divided into two groups, with half receiving Zilmax at the recommended dose and half not receiving it. On the last day of the trial, four days after Zilmax supplementation was discontinued, heifers were exposed to a simulated stress event to mimic the stress response that would be anticipated in cattle being shipped from the feedlot to packing plant. At the conclusion of the trial, heifers were harvested at UNL and their hearts, liver, lungs, kidneys and adrenal glands were studied.

Results from the study show how differences in physiological and endocrine markers of stress and muscle accretion in heifers that were supplemented with Zilmax compared to heifers not fed Zilmax. Heifers fed Zilmax had an increase in parameters that indicate increased muscle mass. The increase was expected, as the drug label for Zilmax includes statements pertaining to increases in creatinine and creatine phosphokinase, according to Ty Schmidt, a UNL animal scientist, who worked with colleagues including Jeff Carroll and Nicole Sanchez of USDA-ARS.

Results from this study, he added, also demonstrated that heifers supplemented with Zilmax had a decreased production of the stress hormone cortisol, and decreased body temperature during the simulated stress event. Histopathology of the heart, lungs, liver, kidneys and adrenal glands revealed some differences between the heifers supplemented with Zilmax and the heifers not receiving Zilmax. The livers and right adrenal gland of the Zilmax heifers were slightly smaller than heifers that were not fed Zilmax, but there was no difference in lungs, kidneys, or heart.

“Overall, the results of this trial indicate that while there are variations in the body temperature, endocrine and metabolic parameters and histopathology of major organs of Zilmax supplemented heifers, these differences are minor and show no indication that supplementation of Zilmax is detrimental to the health or well-being cattle,” Schmidt said.

In addition to Schmidt, Carroll and Sanchez, others who participated in the study were: Steve Jones and David Steffen, UNL; and graduate students Joe Buntyn and Sara Serien, also of UNL.

Merck has plans for a study on a much larger scale. The plan, including 250,000 cattle, would require support of several feedlots and meatpackers, who have yet to jump on board.

Tyson was the first beef packer last August to announce the decision to stop buying cattle fed with the supplement, sending cattlefutures prices surging over tight beef supply concerns. Cargill followed suit in October, with indefinite plans, “until we are 100 percent confident the animal welfare issues are resolved.”

Zilmax was approved for use in 2006 and debuted in the U.S. in 2007. Cargill was the last major beef packer to allow cattle fed Zilmax into its beef supply chain, in 2012. Cargill studied Zilmax for years prior to doing so. One reason Cargill was initially reluctant to accept cattle fed Zilmax was a series of extensive beef tenderness tests that created concern about potential impact to product quality, according to a Cargill press release. From 2006 to 2012, best practices were developed by the company’s cattle procurement and Research & Development teams to ensure product quality.

By 2012, some 70 to 80 percent of the U.S. cattle herd was being fed Zilmax or Optaflexx. The latter is a similar growth promotant produced by Elanco that was used for nearly a decade.

The Zilmax debate also spurred some of the U.S.’s partnering countries to implement a zero-tolerance policy on levels of feed additives in beef, despite USDA’s assurance that the additive was safe. China, Russia and the European Union prohibit Zilmax use.

Following the removal of Zilmax, media reports hinted at bigger problems, including another research study that indicated the number of U.S. cattle deaths linked to Zilmax could reach into the thousands.

According to Reuters news service, researchers from Texas Tech University and Kansas State University found that more than 3,800 Zilmax-fed cattle died in 2011 and 2012, with between 40 percent and 50 percent of deaths likely attributable to Zilmax. Those numbers run more than tenfold the 285 deaths Merck reported during six years of Zilmax sales.

The study, conducted by Meat Scientist Dr. Guy Loneragan was published in PLOS ONE. Merck released a statement in response to the study, challenging the methods and assumptions.

“Only a well-designed clinical study, in a real world setting coupled with analysis of data by third-party industry experts, can thoroughly confirm the safety profile and performance of a product,” the company wrote.

Pointing out a number of scientific studies of its product, Merck concluded, “Dr. Loneragan’s opinions are based on observational information and we disagree with them. “Using observation analyses where cattle are not randomized and where rigorous scientific procedures are not utilized, is not a respected scientific method to rigorously evaluate the safety and efficacy of any product.”

Beef Additive Alert, touting itself as a “national consumer awareness campaign founded by two veteran cattle ranchers who seek to preserve USA beef quality, consistency and integrity,” pointed out that the UNL research only involved 20 heifers, “in an industry that processes 600,000 cattle per week.”

The study also declined to examine consumer concerns about residues and overall beef quality. “We don’t think FDA-approved beta agonists belong in the meat industry at all. We are concerned about decreased quality and tenderness. We are in the beef business, not the chemical business,” said co-founder Harvey Dietrich.

“We applaud the USA’s largest beef processors for their continued integrity. We are very hopeful that the industry does not back down. They’re thinking about animal welfare and the consumer. So are we,” said Beef Additive Alert’s Communications Director Susan Stern. — Traci Eatherton, WLJ Editor

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