Despite new research into beta agonists, Zilmax still out of US market

By Aerin Einstein-Curtis

- Last updated on GMT

Despite new research into beta agonists, Zilmax still out of US market
The question of if or when Zilmax will return to the US market remains unanswered despite recently published research into fatigue cattle syndrome and use of beta-agonists showing the cause to be ‘multifactorial’.

“There is no set timeline to end the sales suspension, and the company remains committed to its review work. At this point, nothing has changed with regard to the situation with Zilmax,”​ a spokesperson for Merck Animal Health told FeedNavigator this week.

That drug maker temporarily pulled the growth-promoting additive from the US market over two years ago.

The muscle-building drug, which is fed to cattle during the last few weeks they are in feed yards, was approved by the FDA in 2006, but its safety was called into question in August 2013 when it was claimed it caused lameness in cattle.

Merck began a multi-step review process for use of the additive after questions started. The work included re-certifying industry members who use the additive, reviewing best management practices and getting input from industry advisors on the product and its use.

Zilmax’s label was altered to include a lower-dose method and a caution statement, said the company. Field studies, witnessed by a third-party, were also said to have got underway.

Industry concerns remain

US beef processors, including Cargill and Tyson Foods, said their policy is unchanged regarding the supplement. Both stopped buying cattle fed Zilmax over the concerns it was linked to cattle mobility difficulties.

Cargill halted its purchase of cattle that had been fed the additive in August 2013 pending more research and information. Indeed, one of its cattle industry specialists served on Merck’s advisory board formed to evaluate ongoing research into the beta-agonist.

That panel comprised representatives from packers, large, medium and small cattle feeder operations, cow-calf producers, veterinarians, academia and industry consultants. 

However, a spokesperson said this week: “Cargill has not changed its position regarding the use of Zilmax, and we are not accepting cattle fed Zilmax.”

“This is not a food safety issue,”​ Tyson officials said. “It’s about animal well-being and ensuring the proper treatment of the livestock we depend on to operate.”

Research findings

Research​ published in the Journal of the American Veterinary Medical Association​ into fatigue cattle syndrome and use of beta-agonists found the cause to be “multifactorial”​ and to likely involve issues including heat and the time of day animals were transported along with animal weight.

The scientists involved also found it is possible for cattle that had not been fed a beta-agonist to develop and display the same symptoms.

“Although anecdotal evidence generated concern that cattle fed the adrenergic receptor agonist zilpaterol hydrochloride were at greater risk of developing mobility problems, compared with cattle not fed zilpaterol, this condition is likely multifactorial,”​ said the authors, which included Daniel Thompson from KSU and Guy Loneragan from Texas Tech.

Additional factors may include season as the mobility problems and other reactions were rarely reported outside of summer months, the group said.

And, since 2000, the mean carcass weights for finished steers have increased from a range of 771 to 795 lb (350 to 361 kg) to a range in 2012 of 860 to 871 lb (391 to 396 kg). Also, how the cattle were handled and how far they traveled to the trailer could be risk factors.

“Results of a study conducted by our laboratory group indicate that the serum lactate concentration and CK activity did not differ significantly among zilpaterol-fed steers, ractopamine-fed steers, and steers not fed ­-adrenergic receptor agonists that were maintained in a typical feedlot setting with minimal exposure to stressors,”​ the group said.

The association between use of a beta-agonist, like Zilmax, and the mobility challenges and symptoms that cattle displayed had originally arisen after a similar link was made between use of the beta-agonist ractopamine and fatigued pig syndrome, the scientists said. 

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