“We can’t lose this technology; it’s too valuable. But that doesn’t mean that it doesn’t come at a price or without responsibility,” says Dan Thomson, DVM, Jones Professor of Production Medicine and Epidemiology at Kansas State University.

He’s talking about beta-agonists and the recent debate about their role, if any, in lame, lethargic and non-ambulatory cattle at the packing plant.

In August, Tyson Fresh Meats suspended purchase of cattle fed Zilmax® (zilpaterol hydrochloride), citing concerns that it might be causing ambulatory problems in cattle.

Soon after Tyson’s announcement, Merck Animal Health, maker of Zilmax, voluntarily and temporarily suspended sales of the feed additive in the U.S. and Canada to address these concerns.

“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,” explained KJ Varma at the time. He is Merck Animal Health’s senior vice president of global research and development.

Zilmax is one of two beta-agonists approved for use in the U.S. The other is Elanco’s Optaflexx® (ractopamine hydrochloride). The products increase feed efficiency and partition more dietary energy to the deposition of muscle rather than fat. They are approved for feeding to cattle during the last phase of the finishing period. Beta-agonists fed to cattle pose no threat to human health.

More than one contributor

“I believe we’ll see issues of slow-moving and non-ambulatory cattle whether or not they’re fed beta-agonists,” Thomson says. “In the cases of cattle I’ve examined with these issues, their blood profile is eerily similar to that of pigs with fatigued-pig syndrome [FPS].”

A fact sheet from the University of Florida defines FPS as “pigs without obvious injury, trauma or disease that refuse to walk or keep up with contemporaries.” Thomson says pigs with FPS often recover after 4-6 hours of rest. He adds that FPS is different than porcine stress syndrome (PSS), a genetic recessive disorder that makes pigs more susceptible to stress.

“In some of the cases we’ve examined, very preliminary findings indicate we should also be looking at a genetic predisposition to stress in cattle,” Thomson says. “Bovine stress syndrome [BSS] has been documented in Australia. Based on discussions and descriptions of the clinical signs, matched with serum chemistry from affected animals, I do think we have fatigued-cattle syndrome [FCS]. It could be related to or different from BSS, but both are related to stress.”


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In a fact sheet for pork producers at porkgateway.org, “Management Strategies to Reduce Transport Losses in Market Weight Pigs,” authors say that transport losses are influenced by many factors. Among these are handling intensity and handling tools, genetics, social hierarchy and pecking order, facility design, management (presorting market-weight pigs prior to loading), and transportation (trailer design, mixing unfamiliar pigs during transport, transport floor space, and transport time/distance). Packing plant conditions (waiting time prior to unloading, unloading procedures and lairage time), and environmental factors (season, temperature and relative humidity) are other considerations.

Similar factors are now being explored in near-finished and fed cattle.