After Merck Animal Health temporarily suspended sales of its Zilmax feed additive in August 2013, industry analysts speculated on the potential impacts on slaughter weights and beef production. In response to our article titled “Will beef production plummet with Zilmax suspention?,” Kansas State University Extension feedyard specialist Chris Reinhardt, PhD, recently provided the following updated analysis:

“I was curious if the sources you cited had taken into account not only the difference in expected carcass weights due to the change in beta agonists, from Zilmax to Optaflexx, but also by the possible reduction in number of days fed.

I agree that cheaper corn will encourage feeders to feed longer, and deeper into Yield Grade 3.

However, the drugs are very different in terms of how they affect carcass lean and carcass fat. After Zilmax began to increase market penetration, it became obvious how dramatically Zilmax shifted fat deposition to lean, and Yield Grade and marbling were reduced proportionately. Producers added 23 days to the feeding program, which allowed them to market at a very similar Yield Grade endpoint, and recover much, if not all of the marbling reduction incurred from Zilmax administration.  

Optaflexx really has little if any impact on Yield Grade when cattle are marketed at similar days on feed versus negative control.  So producers have no incentive to increase the number of days on feed due to changes in fat-to-lean composition like they commonly did when using Zilmax.

If cattle are still gaining 3 pounds per day during those final, additional 23 days, and producers quit feeding those extra days to avoid going into discount Yield Grade 4 territory, we can expect to give up 60 to 70 pounds live weight just from reduced days on feed.  This is in addition to the roughly 10- to 20-pound difference in weight due to changing products.

So if 33 percent of the fed cattle were on Zilmax before September 1, 2013, and the total net reduction from switching from Zilmax to Optaflexx is 90 pounds live weight, we could then lose a cumulative pounds of live weight across the marketplace.  That's probably a high-end estimate.  

Steer live weight was down 15 pounds versus 2012 as of the Dec. 27 in the USDA National Daily Cattle and Beef Summary; carcass weights for Texas, Okla. and N.M. look to be down 15 pounds versus 2012 as of the Dec. 30 USDA Daily Direct Steer and Heifer Slaughter Cattle Summary.”