Sale of Zilmax supplement suspended after Tyson says it won’t buy cattle fed it


SUMMIT, N.J. — Merck Animal Health has temporarily suspended sales of its cattle feed additive Zilmax in the United States and Canada.

The decision was made after Tyson Food announced in a letter to beef suppliers early this month it would buy no cattle fed with Zilmax, pending an investigation into incidents of cattle lameness.

In an Aug. 8 statement, Merck officials said they were “surprised by Tyson’s letter. We are confident that, based on all of the available data on Zilmax, the experience reported by Tyson is not attributable to Zilmax.”

But the animal drug manufacturer temporarily suspended sales anyway.

In a public statement, Merck Animal Health said it believes “in the science that supports Zilmax and are confident in its safety and performance,” but in conjunction with independent experts, the company will conduct a scientific audit, “which will monitor the process of feeding of Zilmax, and will 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.”

“We also will do a thorough review of potential compounding factors — such as nutrition, transportation and receiving facilities.”

Merck said the suspension will give it time to create valid study protocols, identify feeders and packers to participate in the audit, and create of a third-party team to oversee and validate its results.

“We remain confident in the safety of the product, based on our own extensive research and that of regulators and academic institutions, and are committed to the well-being of the animals that receive it,” said KJ Varma, BVSc, Ph.D., Diplomate ACVCP, senior vice president global R&D, Merck Animal Health.

Feed additive

Zilmax is a medicated feed additive for finishing cattle, in a class called beta-agonists, with the active ingredient zilpaterol hydrochloride. It is not a steroid, and is approved by the FDA for use in cattle only, and only in steers and market cattle, not breeding cattle.

According to a fact sheet created by Jason Cleere, beef cattle specialist at Texas A&M University, that active ingredient has been shown to increase rate of weight gain, improve feed efficiency, increase rib eye area and increase red meat yield in feedlot cattle.

Zilmax sales in the United States and Canada were $159 million in 2012.

According to one source, an estimated 80 percent of beef cattle are fed Zilmax and competing additives like Optaflexx.


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  1. I feed my angus a mix of sweet feed,fine cracked corn and oats and loose mineral.Plus they are on grass 24/7. in the summer they only get grain when they come up to the barn and stand in front of thier feeders wanting it whitch is usualy once a day every other day or so.In the winter i feed the same plus beet pulp pellets mixed in and if it is realy cold some alfalfa pellets mixed in plus hay 24/7 and mineral.My cattle keep good wieght and look good all year round.I raised three bottle jersey calves and sole them for butcher,the people that bought them said they were lean and very tasty so i must be doing something right.My calves are born healthy and are fasr growers.I’ve never added any growth chemicals to thier feed they do fine without it.


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