For more than a year, a once-popular
drug that makes cattle put on
weight faster has been stuck in a kind of veterinary purgatory.
As
far as the Food and
Drug Administration is concerned, the drug, Zilmax,
is legal to use. But large meat packers, which dominate the industry,
have ostracized it after the drug was accused
of making animals suffer. The drug's manufacturer, Merck, has been
working on a plan to rehabilitate it. But that effort has stalled.
Merck suspended sales of Zilmax in August 2013, after Tyson, a leading beef processor, announced
that it would no longer buy cattle that had been treated with Zilmax,
and other cattle buyers followed Tyson's lead. Tyson's move followed
reports that Zilmax-treated cattle were more likely to suffer from what
some researchers call "cattle fatigue syndrome." At an industry
conference, an animal welfare expert from the meat packer JBS showed a
video of Zilmax-treated cattle that appeared immobile, unable to move
properly.
Merck responded with a "five-step plan" to examine the safety of Zilmax. Last November, it unveiled
new procedures for using the drug, including guidelines and training
that are intended to prevent overdosing cattle with the drug.
But
the centerpiece of Merck's plan, a large "field evaluation" of Zilmax,
remains in limbo. This study was supposed to include up to 240,000
cattle, at a variety of commercial feedlots. Merck recruited a
university researcher to carry it out, and it was supposed to begin last
year.
Feedlot operators are refusing to participate, though,
because they don't want to be stuck with cattle that they can't sell.
And their customers, the beef processors, remain skittish. "We're not
accepting cattle fed with Zilmax," says Mike Martin, from Cargill, one
of four companies that dominate the beef industry. (The others are
Tyson, JBS, and National Beef.)
Cargill's reluctance to take Zilmax-fed cattle, Martin says, is based
in part on continued uncertainty about what caused those health
problems in cattle. But he also mentioned another reason: The drug can
complicate beef exports. Some countries won't accept beef from cattle
that were fed Zilmax.
Kelly Goss, a spokesperson for Merck
Animal Health, says that organizing the Zilmax study has "been more time
intensive and complicated than we anticipated." But she says the
company still hopes to proceed with it. "Our intent is not to rush
this," she says.
Zilmax is part of a class of drugs called beta
agonists, which are chemically similar to the human hormone adrenaline.
Another beta agonist, called ractopamine, is commonly fed to pigs. They
cause animals to grow more muscle.
Dan Thomson,
a researcher at Kansas State University who has studied the effects of
Zilmax on cattle, says that Merck has been acting responsibly in its
efforts to revive sales of the drug. "I think that the changes they've
made have been all for the better," he says.
Thomson also says
that beta agonists such as Zilmax are not the sole cause of "fatigued
cattle syndrome." Those symptoms, he says, are a reaction to stress.
Beta agonists may contribute to it, but so do heat, being transported in
trailers and interactions with humans. "We have been able to study it
in cattle that were fed beta agonists and cattle that were not fed beta
agonists," he says.