Merck went on the offensive immediately upon Tyson's move, releasing a statement emphasizing its commitment to animal well-being. Merck cited the benefits and safety of Zilmax documented over a 30+ year history of research and development and rigorous testing.

A few days later, Merck added that it would “vigorously pursue all reported adverse events, whether or not they are deemed related to the product.” Central to this effort was its “Five-Step Approach to Ensuring Responsible Beef,” which Merck said it would operate in conjunction with independent experts.

The program would consist of a scientific audit to monitor the process of feeding of Zilmax, and would follow identified cattle from the feedyard to the packing plant to determine potential causes of lameness and other mobility issues during feeding, transportation, offloading and staging at the processing facility. Merck said it also would conduct a thorough review of potential compounding factors – such as nutrition, transportation and receiving facilities.

However, the next day, Aug. 16, the company announced it was temporarily suspending sales of Zilmax in the U.S. and Canada. Merck said it was doing so to ensure effective implementation of its five-step plan.

“This will allow sufficient time for the establishment of valid study protocols, identification of feeders and packers to participate in the audit, and creation of a third-party team to oversee this process and validate its results,” the release said.

K.J. Varma, Merck’s senior vice president of global R&D, said the temporary suspension “demonstrates our commitment to providing our industry partners with data that will reaffirm confidence in Zilmax. We sincerely regret that this situation creates business challenges for our customers but it is critical to ensure that this process is conducted appropriately and with rigorous scientific measures. After the five-step plan is completed, the results will be shared publicly."

The release also said Merck was accelerating its development of an animal health advisory board consisting of industry experts, producers, academics and company leadership “to promote an open dialogue on animal well-being and help shape and strengthen the company's animal health and well-being program in the future.”

Before Merck’s voluntary withdrawal of Zilmax, Glynn Tonsor, Kansas State University economist, characterized the situation as fluid. After all, nothing guarantees that Tyson, or the other three packers, won’t reverse their policies.

But Tonsor says Tyson’s announcement makes less beef volume a certainty in the coming months. “We’ll produce less, but how much less depends on how many people disadopt the use of Zilmax. Will Tyson be alone, and to go further, what portion of their recent suppliers will simply switch processing plants or move from Zilmax to Optaflexx?” he asks.

If such a switch occurs, Tonsor says the beef industry likely won’t see a huge reduction in beef volume. “At the margin, there’s said to be a better gain for Zilmax, but if Tyson’s suppliers just move to Optaflexx, I don’t think we’ll see aggregate projections impacted all that much,” he adds.