What are beta agonists?

Jon Condon, 15/07/2013

As Australia begins to consider whether it wants to adopt the use of beta agonists in beef production, it's important to understand what the compounds are, and how they work.

Beta agonists act as a growth promotant, mimicking the effect of naturally occurring hormones at the cellular level. But unlike conventional Hormonal Growth Promotants, they do not affect the hormone status of the animal.

Originally developed for the treatment of asthma in humans, there appears to be little question that beta agonists present no risk to human health.

The compounds were first approved by the US Food and Drug Administration for use in cattle in 2005, and in 2000 for pigs. In South Africa, they have been used in livestock production for 17 years.

In beef production, beta agonists are exclusively used in cattle in intensive feeding operations on higher planes of nutrition, rather than those in open range conditions.

The compounds act as a repartitioning agent in livestock, changing the metabolism of the animal by converting more feed energy into muscle, rather than fat. The results are also very predictable, meaning cattle feeders can administer the product for a certain production outcome. 

The two most common beta agonists used on US beef cattle are Optaflexx (ractopamine hyperchloride) and Zilmax (zilpaterol hydrochloride). The word, ractopamine, is sometimes incorrectly used as a proxy to describe the broader group of beta agonist compounds.

While cattle nearing maturity naturally begin to deposit additional fat and less muscle during the final stages of the grainfeeding period, those receiving beta agonist during the last 20-30 days demonstrate a feed-to-gain ratio increase of 10-25pc; their muscle gain increases while their fat deposition reduces at the same time.

Weightgain advantage in beef cattle over a typical finishing period is about 8-9kg. Feed efficiency is often improved by 14-21pc. The productivity gain is independent of that achieved with HGPs, and the two can be used simultaneously.

Zilmax typically also produces an additional 1.5pc of meat yield in the meatworks chillers, over and above the weightgain advantage. That means that the supply-chain productivity impact is seen not only at the feedlot level, but at the processor level as well.

See this morning’s companion articles:


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