Merck Animal Health last week refuted a study published March 12 by a Texas Tech University veterinary epidemiologist that suggests cattle fed beta agonists have higher mortality rates.
Beta agonists are often fed for leaner beef and improved efficiency in cattle destined for slaughter.
The peer-reviewed article was published in PLOS ONE. It's authored by Texas Tech's Guy Loneragan and co-authored by Daniel Thomson and Morgan Scott of Kansas State University.
While cattle on beta agonists require less feed and less water to produce the same amount of beef than if no beta agonists were used, the study finds that it may impact animal welfare.
"Through our extensive analysis, we found that the incidence of death among cattle administered beta agonists was 75 to 90 percent greater than cattle not administered the beta agonists," Loneragan said.
"This increase in death loss raises critical animal-welfare questions. We believe an inclusive dialogue is needed to explore the use of animal drugs solely to improve performance, yet have no offsetting health benefits for the animals to which they are administered. This is particularly needed for those drugs that appear to adversely impact animal welfare, such as beta agonists."
Related: Merck Suspends Production of Its Beta Agonist
Popular beta agonist Zilmax was pulled off the market last fall on concerns that it negatively impacted animal welfare. In that case, animals were reportedly having mobility issues.
Manufacturer of Zilmax, Merck, subsequently presented a five-step audit on the product and its recommended administration to probe the mobility concerns; the company maintained that the product was safe to use, according to extensive reviews by worldwide regulatory agencies.
Beef processors Tyson and Cargill, however, discontinued purchases of meat from cattle fed beta agonists.
By December, Merck was working to implement its five-step plan, detailing in a press statement that it had made "considerable progress" towards the plan's goals, but had no timeline for returning Zilmax to the market.
Of Loneragan's study, the company says his opinions are "…based on observational information and we disagree with them."
Merck said the using observational 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."
The company suggested caution when interpreting results of Loneragan's study. However, they underscored proper response to questions of product safety.
"We take any adverse event report very seriously and investigate each one thoroughly, often utilizing independent experts to provide additional support, knowledge and expertise," the Merck statement continued. "We are committed to adhering to all regulatory guidelines."