Beta-agonists as the cause of welfare issues there were described by some panelists as "anecdotal."
Lily Callaway, a member of JBS's animal welfare team, told the symposium her company was also seeing increased incidences of ambulatory stress in steers delivered to the company's processing facility. JBS may be the nation's largest beef packer following its January acquisition of XL Foods. Callaway said the company slaughters 18,000 fed cattle per day.
"Truck drivers have indicated that there is a difference between loading cattle depending on the beta-agonist status of the diet," Callaway explained. "Our plants have indicated that particular lots of cattle are showing up as 'tender footed,' they do not want to move, seem lethargic and stiff and have no energy."
Callaway, who completed her Ph.D. under animal welfare expert Temple Grandin, showed a video of stressed cattle unloaded at a JBS facility, depicting animals that did not respond with a typical flight response to workers' attempts to move the animals through the facility, and appeared to move uncomfortably on their feet and legs.
Data compiled at two JBS facilities appeared to support Callaway's comments on animal movement issues. In one example, of 8,000 head processed over three shifts, at least 20% were classified as "difficult to move," 82% of which were fed beta-agonists. At least 35% of the cattle slaughtered at the facility during the reference time period were fed a beta-agonist.
In a second example, 4,300 head were processed over two shifts at a different JBS plant. In that instance 28% were "difficult to move," and 92% of those were fed beta-agonists. Callaway said at least 47% of the cattle slaughtered in this time period were fed beta-agonists.
Beta-agonists are fed to cattle only in the final 20-40 days on feed, according to federal regulations. Zilmax has a three-day withdrawal period prior to slaughter. The other beta-agonist on the market, Optaflexx from Elanco, does not have a withdrawal period.
Merck responded: "We are confident that, based on all of the available data on ZILMAX, the experience reported by Tyson is not attributable to ZILMAX. Indeed, Tyson itself points to the fact that there are other possible causes and that it does not know the specific cause of the issues it recently experienced."
Merck said its safety data "included rigorous animal health safety and well-being studies - conducted by university experts" and this data showed the behavior and movement of cattle fed Zilmax is normal.
"Merck Animal Health has offered technical assistance, both internal and external experts, to help Tyson to understand what is behind the instances at its facility," said Merck officials. "Merck Animal Health is confident in the extensive research and data behind the product and the fact that its safety has been well demonstrated."
Vance is livestock editor for Feedstuffs weekly agribusiness newspaper.