A closer look at Zilmax
by Erica Shaffer
KANSAS CITY, Mo. – Beta-agonists like Zilmax have gotten a bad rap in the livestock industry, but a team of scientists at the Univ. of Nebraska-Lincoln (UNL) believe the problem of lameness in cattle fed Zilmax might lie in other factors.
Ty Schmidt, an assistant professor of Animal Science at UNL, planned to conduct a study of beta-agonists before the scuttlebutt over Zilmax broke out during 2013. Schmidt said most of the recent discussion about Zilmax was based on anecdotes, not scientific data.
"Let's find the truth — is it an animal welfare problem, or not?" he said.
So, a team of researchers, including Schmidt, set out to determine what impact, if any, Zilmax was having on cattle well-being. The team chose a sample of 20 Angus heifers from a heard a nutrition group at the university had been using throughout the summer.
"We picked out the best we could utilize — they had no lameness no health issues," Schmidt said. The heifers weighed roughly 1,300 lbs. each.
The study was conducted over 26 days. Scientists collected blood samples and body temperatures from 20 heifers, in addition to video images of the animals. The animals remained at the facility until harvest.
The heifers were divided into two groups with half receiving Zilmax at the recommended dose of 7.56 grams per ton of feed -- and half not receiving the additive. The heifers were kept in individual stalls and hooked up to catheters, almost like patients in a hospital. The research environment was very controlled, Schmidt said.
Researchers induced a stress challenge by giving the heifers hormones that are naturally produced in their bodies — corticotrophin-releasing hormone and vasopressin. This stress event occurred on the last day of the trial, four days after Zilmax supplementation ended.
"By challenging them with those two hormones, we actually caused their bodies to secrete cortisol, one of the stress hormones," Schmidt said.
The cattle were slaughtered, and researchers studied the animals' hearts, liver, lungs, kidneys and adrenal glands.
The study revealed some differences in physiological and endocrine markers of stress and muscle gain in heifers that were fed Zilmax. The Zilmax heifers also had decreased production of cortisol, a stress hormone, and decreased boy temperature during the simulated stress event. However, Schmidt said, these differences are minor and show no apparent detrimental effect on cattle health.
Springdale, Ark.-based Tyson Foods was unmoved from its position on Zilmax despite the promising results. It was the first large beef processor to stop buying cattle fed Zilmax. Merck Animal Health, which manufactures the feed additive, pulled Zilmax from the US and Canada after Tyson Foods notified its cattle suppliers in August 2013 the company would stop accepting cattle fed with Zilmax after receiving animals at some of its beef plants that had difficulty walking, or were unable to move. Zilmax sales in the US and Canada totaled $159 million in 2012. Merck Animal Health commissioned its own Zilmax study.
"We're aware of the study, but have not changed our position," the company said in a statement.
"They're going to have to make their own decisions," Schmidt said. "I can't tell them what decision to make in terms of their own companies. I can tell, from the trial we did, I don't have any reservations about feeding Zilmax based on what we got from our study."
Schmidt has some ideas about the causes of lameness. "I think the cattle are just a lot bigger; we're feeding cattle until they're 1,400 to 1,500 lbs.," Schmidt said. "I'm not sure they're designed to handle that much weight as a steer or a heifer. We need to look at the industry as a whole and see are we providing the proper facilities for these animals to unload on.
"From the data we've got, it doesn't look like Zilmax is the problem," he added.
The UNL research has been criticized as a small study, and Schmidt agrees — number-wise it is a small study. But the research also represents an intensive effort to collect data from cattle being fed a beta-agonist.
"We put close to 5,000 man hours, we collected close to 2,000 blood samples and we put close to $200,000-$300,000 into it. It was a small study because it's an intensive study. It's a win-win for us because whatever we found was going to be important data."
The team is working to publish two papers on the Zilmax research by August in the Journal of Animal Science