Profit Tip: Feed Additives

May 2017

When profit margins are tight, the use of technologies such as feed additives should not be overlooked. Feed additives are compounds fed to feedlot cattle for reasons other than supplying nutrients. These compounds increase the rate of gain and feed efficiency of beef cattle, decreasing the cost of production and improving the profit potential of feedlot producers. Here, we will focus on ionophores and beta-agonists.

Ionophores (for example, Rumensin, Bovatec, Gainpro, etc.) are compounds commonly fed to feedlot cattle. These products target the ruminal bacterial population and alter the microbial ecology of the rumen, causing a shift in volatile fatty acids produced toward more propionate, with associated reductions in acetate and butyrate. Ionophores improve cattle feed efficiency, and that is what has made these compounds such important tools to feedlot producers. Feeding ionophores will improve feed efficiency 3% to 10%, depending on the diet. Although original research showed 10% improvement in feed conversion, recent research shows 3% to 4% improvement. (The difference is likely a result of changes in ration energy level.) Ionophores also reduce the risks of acidosis and bloat. With all these benefits, ionophores are a good investment, as the cost of feeding is only a few cents per head per day.

Beta-agonists are a relatively new technology that can markedly impact profitability of finishing cattle. These compounds are "repartitioning agents" that shift nutrients away from fat deposition toward lean muscle growth. Two beta agonists are available to cattle feeders: ractopamine hydrochloride (Optaflexx; Elanco Animal Health) and zilpaterol hydrochloride (Zilmax; Merck).

Optaflexx is approved for feeding during the last 28 to 42 days of the finishing period (100 to 300 mg/head/day). When fed at the recommended dose (200 mg/day), data have shown that body weight and carcass weight are increased, with no increase in feed intake, resulting in improved feed efficiency. There is no withdrawal period for Optaflexx.

Zilmax is fed to feedlot cattle during the last 20 to 40 days on feed (60 to 90 mg/head/day). Zilmax benefits include increased live weight gains, increased average daily gain, increased carcass weight and improved feed efficiency. Zilmax must be withdrawn from cattle three days before slaughter. Before feeding Zilmax, feeding operations must complete a mandatory training program through Merck. Currently, most major packers will not harvest cattle fed Zilmax.


  • Use ionophores. The cost to benefit ratio of ionophore usage has been estimated to save the cattle industry approximately $1 billion per year (Callaway et al., 2003).
  • Including either Optaflexx or Zilmax in finishing diets is a very cost effective, convenient, and efficient way to increase growth rate, improve feed efficiency, increase dressing percent, and improve carcass meat yield of feedlot cattle (Dikeman, 2007).
  • While both beta-agonists available to feedlot producers could have negative effects on carcass quality grade (marbling), this seems to be more pronounced with Zilmax.
  • The type, dose, and duration of beta-agonists should be matched to specific market objectives.
  • Always follow label directions with regard to dosage of additives.


Rob Eirich, Nebraska Extension Educator
Director of Beef Quality Assurance
University of Nebraska–Lincoln


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  • Callaway, T. R., T. S. Edrington, J. L. Rychlik, K. J. Genovese, T. L. Poole, Y. S. Jung, K. M. Bischoff, R.C. Anderson, and David J. Nisbet. 2003. Ionophores: Their use as ruminant growth promotants and impact on food safety. Curr. Issues Intest. Microbiol. 4: 43-51.
  • Dikeman, M.E. 2007. Effects of metabolic modifiers on carcass traits and meat quality. Meat Sci. 77: 121-135.