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Meatpacking giant Tyson recently grabbed headlines when it announced it would no longer buy and slaughter cows treated with a growth-enhancing drug called Zilmax, made by pharma behemoth Merck. Tyson made the move based on “animal well-being” concerns, it told its cattle suppliers in a letter, adding that “there have been recent instances of cattle delivered for processing that have difficulty walking or are unable to move.” According to the Wall Street journal, Zilmax (active ingredient: zilpaterol hydrochloride) and similar growth promotors are banned in the European Union, China, and Russia.

The news sent shock waves through the beef industry. Merck denied any problems with its drug but announced it would temporarily suspend sales of Zilmax in the United States and Canada pending a “scientific audit” of the product, which generated $159 million in US and Canadian sales in 2012, Merck added. Soon after, Tyson rivals JBS, Cargill, and National Beefpacking announced that they, too, would stop accepting Zilmax-treated cattle for slaughter, pending Merck’s review.

Together, Tyson, JBS, Cargill, and National slaughter and pack more than 80 percent of the beef cows raised in the United States, according to University of Missouri researcher Mary Hendrickson (PDF). If they stick to their refusal to buy cows treated with the drug, it’s hard to see how Zilmax has a future on America’s teeming cattle feedlots. Is the US beef industry turning away from the practice of turning to drugs to fatten its cattle?

Not so fast. Rather than wean themselves from growth promoters, the companies that produce cows to supply the likes of Tyson and JBS are instead shifting rapidly to a rival beta-agonist, this one from pharma giant Eli Lilly, called Optaflexx. The suspension of Zilmax sales has caused such a “surge in demand” for rival Optaflexx that “Lilly is telling some new customers it cannot immediately supply them,” Reuters reported.