Ractopamine vs. Zilpaterol: Which Feed Additive Gives Steers the Best Finish?
"A side-by-side comparison of how these beta-adrenergic agonists affect growth, carcass quality, and meat tenderness in finishing steers."
In the quest for efficient and high-quality beef production, feed additives play a crucial role. Among these, ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) have gained attention as beta-adrenergic agonists, known for enhancing growth performance and influencing carcass characteristics in cattle. But how do these two additives stack up against each other?
A study was undertaken to compare the effects of RAC and ZH when administered to beef steers during the final 33 days of the finishing period. The research aimed to provide insights into their comparative effectiveness, particularly concerning growth, carcass traits, and meat tenderness.
Three hundred crossbred beef steers were monitored, divided into groups based on body weight, body condition score, and breed type, and then randomly assigned to one of three treatments: a control group (no beta-agonists), a RAC group (receiving 200 mg of ractopamine.hd. ⁻¹d⁻¹ for 33 days), and a ZH group (receiving 75 mg of zilpaterol.animal. ⁻¹d⁻¹ for 30 days, followed by a 3-day withdrawal period). The results shed light on the distinct impacts of these additives on beef production.
Current Use and Trade Impact
USDA research describes ractopamine hydrochloride as being used in the feedlot industry to increase daily gain, feed efficiency, and hot carcass weight, with minimal negative effects on carcass quality. One experiment cited in the USDA material provided heifers with 400 mg of ractopamine hydrochloride per heifer per day. Many US trade partners, animal sports organizations, and some animal shows prohibit ractopamine use or require animals and carcasses to be ractopamine-free. Residues can therefore lead to disqualification from import, export, or competition.
Testing and Regulation
The USDA FSIS CLG-RAC1.02 method is suitable for quantifying ractopamine hydrochloride in swine and bovine liver at 25 to 300 ppb and in swine and bovine muscle tissue at 1.0 to 300 ppb. Federal regulations describe Type A medicated articles containing 9 or 45.4 grams of ractopamine hydrochloride per pound. An automated online LC/MS method uses TurboFlow technology to reduce time-consuming preparation such as offline solid-phase extraction while improving throughput and reproducibility. Another application note identifies increasing interest in measuring ractopamine in digestive-tract tissues, or offal, in addition to traditional tissues such as muscle and liver.
From Beta-Agonist Biology to Feed Additive
Ractopamine hydrochloride stimulates beta-adrenergic receptors and has effects similar to epinephrine, along with anabolic effects associated with conserving lean muscle and reducing fat. It is described as a selective beta-1 adrenergic agonist used primarily in swine and cattle during the finishing phase. Research characterizes ractopamine as a synthetic phenethanolamine beta-adrenergic agonist used to promote leanness and improve feed-conversion efficiency. Although authorized for pigs and cattle in a limited number of countries, it is not authorized in many jurisdictions, including the European Union, China, Russia, and Taiwan.
RAC vs. ZH: Unpacking the Performance and Carcass Effects
The study revealed that both RAC and ZH had positive impacts on the steers' final body weight (BW), average daily gain (ADG), feed efficiency (G:F), and hot carcass weight (HCW) when compared to the control group. This indicates that both additives can effectively promote growth and carcass development.
- Growth and Feed Intake: ZH decreased ADG, average daily feed intake (ADFI), and final BW compared to RAC.
- Carcass Weight and Yield: ZH increased HCW and dressing percentage more than RAC. RAC did not affect carcass yield in this study, whereas ZH improved yield grade.
- Carcass Traits: ZH decreased adjusted fat thickness and kidney, pelvic, and heart (KPH) fat, while increasing ribeye area.
- Meat Quality: Marbling, lean maturity, and skeletal maturity were similar across all treatments.
Recent Beta-Agonist Research
A recent review reports that beta-adrenergic agonists can enhance beef-production efficiency, carcass leanness, and emissions intensity while offering consistent economic returns for cattle feeders and beef packers. The research literature includes experiments measuring the effects of ractopamine hydrochloride, zilpaterol hydrochloride, and lubabegron fumarate on live gain and carcass characteristics. A 2023 Frontiers study specifically examined increasing zinc-amino-acid-complex supplementation in beef cattle fed ractopamine hydrochloride, focusing on growth performance, carcass characteristics, and inflammatory response. These studies show that current research is evaluating both additive responses and nutritional factors that may modify them.
Physiological and Market Concerns
In vitro and in vivo studies indicate that ractopamine acts through beta-1 and beta-2 adrenergic receptor signaling in skeletal muscle and adipose tissue, while its psychoactive molecular pharmacology remains poorly understood. The FDA has approved two beta-adrenergic agonists for in-feed administration to cattle fed in confinement for human consumption, but anecdotal reports have raised concerns about possible associations with adverse effects. Ractopamine residues have also been studied in beef muscle, adipose tissue, rendered tallow, and large intestine at different withdrawal times. Separately, uncertainty about market access led some fairs in Michigan and other states to ban ractopamine use in pigs shown at fairs.
Ractopamine Safety Context
The Singapore Food Agency describes maximum allowed levels of ractopamine in meat, kidneys, and liver and presents a lifetime-consumption comparison for a person weighing 60 kg. Under that comparison, the person could consume 6 kg of meat, 0.67 kg of kidneys, or 1.5 kg of liver containing the maximum allowed levels every day without adverse health effects such as increased heart rate, headache, muscle tremors, or high blood pressure. This source addresses ractopamine exposure and regulatory limits rather than directly comparing ractopamine with zilpaterol. Therefore, it supports a safety-limit comparison, not a conclusion about which additive gives steers the better finish.
The Tenderness Trade-Off: What the Study Reveals
One of the most interesting findings concerned meat tenderness. Steaks from RAC-treated steers showed higher Warner-Bratzler shear force (WBSF) values (meaning less tender meat) compared to control steers at 3 and 7 days of aging, but this difference disappeared after 14 days. In contrast, steaks from ZH-treated steers had higher WBSF values than both control and RAC steaks throughout the entire 21-day postmortem aging period. While both beta-adrenergic agonists effectively improve feedlot performance, RAC does not negatively impact WBSF after 14 days, whereas ZH steaks remain less tender than controls even after 21 days.
Market Growth Prospects
Market commentary projects steady long-term growth for ractopamine hydrochloride, attributing the outlook to rising global meat consumption and demand for leaner meat products. Another 2026 market outlook discusses trends influencing the ractopamine hydrochloride market worldwide and in major markets, although the supplied material does not provide a specific forecast figure. A separate market report describes momentum as livestock producers focus on feed efficiency and lean-meat output. It identifies ractopamine as a beta-adrenergic agonist used in cattle, swine, and turkey production to enhance muscle growth while reducing fat deposition.
Environmental Fate and System Effects
A comprehensive investigation examined the occurrence and fate of ractopamine and other growth-promoting compounds during two eight-month cattle-feeding trials and simulated environmental conditions. The compounds studied included trenbolone acetate and its metabolites, melengestrol acetate, and the less commonly studied beta-adrenergic agonist ractopamine. Research cited in the supplied material reports that environmental impacts of beta-agonists in the Langat River basin were generally minimal, while ractopamine contamination released from swine farms was localized. These findings frame ractopamine as both a production tool and a compound requiring attention to fate and transport beyond the feedlot.