When the drug company Merck Animal Health announced plans to suspend sales of its Zilmax feed additive last week, many observers were shocked.
Yet concern about Zilmax and the class of growth-promotion drugs called beta agonists has been building for some time. In an interesting twist, the decisive pressure on Zilmax did not come from animal welfare groups or government regulators: It emerged from within the beef industry itself, and from academic experts who have long worked as consultants to the industry.
Among them is Temple Grandin, a professor of animal science at Colorado State University and a world-renowned expert on how cattle react to their environments. Grandin, whose life is the subject of an HBO biopic, has redesigned slaughterhouses to make them more humane.
Around the summer of 2006, she says, she started seeing a new kind of problem among the cattle, especially when the weather got really hot. "You had animals that were stiff and sore-footed, animals that were reluctant to move," she recalls. "They act like the floor is red-hot. They don't want to put their feet down. And I had never seen these kinds of symptoms before, ever!"
The problems, she says, affect as many as 1 out of every 5 animals. She's become increasingly convinced that the problems result from the drugs called beta agonists.
Beta agonists are similar, chemically, to the adrenaline that our bodies produce. In humans, this class of drugs is used to treat asthma. When fed to cattle or pigs, though, the animals grow more muscle.