Surreal illustration balancing cattle farming technology with high-quality steak preparation.

Unlock Superior Beef: How Feedlot Additives Impact Meat Quality

Reese Marlowe in Science & Nature September 2025 • 4 min read.

"A Detailed Look at Ractopamine and Zilpaterol in Steer Finishing"

In the ever-evolving landscape of beef production, feedlot additives play a crucial role in enhancing efficiency and meat quality. Among these, ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) have garnered attention for their ability to improve growth performance and carcass characteristics in beef cattle. Understanding their impact is essential for producers aiming to optimize their operations and meet consumer demands.

RAC and ZH are β-adrenergic agonists, compounds that mimic the effects of adrenaline and noradrenaline. These agonists bind to β-adrenergic receptors in animal cells, influencing various metabolic processes. This binding can lead to increased protein synthesis, reduced protein degradation, and decreased fat accumulation, resulting in leaner and more muscular carcasses.

While both RAC and ZH share the common goal of enhancing beef production, they differ in their specific effects and regulatory status. RAC has been approved for use in cattle since 2003, while ZH gained approval in 2006. However, concerns regarding meat tenderness have prompted closer scrutiny of their application. This article delves into a comparative analysis of RAC and ZH, examining their impact on growth performance, carcass traits, and meat tenderness in finishing steers.

RAC vs. ZH: Optimizing Growth and Carcass Traits in Beef Steers

Surreal illustration balancing cattle farming technology with high-quality steak preparation.

A study was conducted to evaluate the comparative effects of RAC and ZH when fed to beef steers during the last 33 days of the finishing period. Three hundred crossbred beef steers were randomly assigned to one of three treatments: a control group (no β-agonists added), a RAC group (200 mg of ractopamine per head per day for 33 days), or a ZH group (75 mg of zilpaterol per animal per day for 30 days, with a 3-day withdrawal period).

The results indicated that both RAC and ZH increased final body weight, average daily gain (ADG), feed efficiency (G:F), and hot carcass weight (HCW) compared to the control group. However, when compared to RAC, ZH decreased ADG, average daily feed intake (ADFI), and final body weight, but increased HCW and dressing percentage. Carcass yield was unaffected by RAC, while ZH decreased adjusted fat thickness and kidney, pelvic, and heart (KPH) fat, increased ribeye area, improved yield grade, and increased cut-out yields.

Increased Growth: Both RAC and ZH enhanced growth performance.
Carcass Improvements: ZH reduced fat and increased ribeye area.
Yield Grade: ZH improved carcass yield grade.

Marbling, lean maturity, and skeletal maturity were not significantly different between treatments. Steaks from RAC-treated steers had greater Warner-Bratzler shear force (WBSF) values than control steers at 3 and 7 days of aging, but there was no difference after 14 days. ZH-treated steers had greater WBSF values than both control and RAC steaks throughout the 21-day postmortem aging period. While both β-adrenergic agonists effectively improved feedlot performance, RAC showed no negative effect on WBSF after 14 days, whereas WBSF values for ZH steaks were significantly greater than controls after 21 days.

The Future of Feedlot Additives in Beef Production

RAC and ZH have demonstrated significant potential in enhancing growth performance and carcass characteristics in beef steers. However, their impact on meat tenderness requires careful consideration. While RAC shows no negative effects on WBSF after 14 days of aging, ZH can lead to greater WBSF values even after extended aging periods. Balancing these attributes is essential for optimizing feedlot practices and meeting consumer expectations for tender and high-quality beef. Further research is needed to refine the application of these additives and explore new strategies for mitigating any adverse effects on meat tenderness.

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Everything You Need To Know

What are ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH), and how do they work in beef cattle?

Ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) are both beta-adrenergic agonists used as feedlot additives in beef production. They mimic the effects of adrenaline and noradrenaline by binding to beta-adrenergic receptors in the animal's cells. This action leads to increased protein synthesis, reduced protein degradation, and decreased fat accumulation. The overall effect is the production of leaner and more muscular carcasses, which are desirable traits in beef production.

What is the difference between the effects of ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) on growth performance and carcass traits?

Both RAC and ZH improve growth and carcass characteristics. In a study comparing their effects, both increased final body weight, average daily gain (ADG), feed efficiency, and hot carcass weight (HCW) compared to a control group. However, ZH decreased ADG, average daily feed intake, and final body weight compared to RAC, but increased HCW and dressing percentage. ZH also reduced fat thickness and kidney, pelvic, and heart fat, while increasing ribeye area, improving yield grade, and increasing cut-out yields. RAC showed no negative effect on Warner-Bratzler shear force (WBSF) after 14 days of aging, while ZH showed increased WBSF values even after 21 days, potentially affecting meat tenderness.

How do ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) affect meat tenderness, and why is this important?

The impact on meat tenderness is a key consideration. Steaks from steers treated with ractopamine hydrochloride (RAC) showed no significant difference in Warner-Bratzler shear force (WBSF) values compared to controls after 14 days of aging. However, steaks from zilpaterol hydrochloride (ZH)-treated steers exhibited greater WBSF values than controls throughout the 21-day postmortem aging period, which suggests that ZH may negatively impact meat tenderness. Meat tenderness is crucial for consumer satisfaction, and any treatment that affects this trait requires careful evaluation to maintain high-quality beef production.

How does the use of ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) influence feedlot practices and consumer expectations?

The use of ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) has the potential to optimize feedlot practices by improving growth performance and carcass characteristics in beef steers. However, their impact on meat tenderness must be carefully considered. Balancing the benefits of increased growth and carcass yield with consumer expectations for tender, high-quality beef is essential. The potential for increased WBSF values with ZH requires attention, and further research is needed to refine the application of these additives and explore strategies to mitigate any adverse effects on meat tenderness, ultimately meeting consumer demand for palatable and desirable beef products.

What are the regulatory statuses of ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH), and how does this impact their use in beef production?

Ractopamine hydrochloride (RAC) was approved for use in cattle in 2003, while zilpaterol hydrochloride (ZH) gained approval in 2006. This regulatory approval allows producers to use these beta-adrenergic agonists to improve growth performance and carcass traits. However, regulatory scrutiny is ongoing, particularly concerning meat tenderness. While RAC shows no negative effects on WBSF after 14 days of aging, ZH can lead to greater WBSF values even after extended aging periods. The differences in the regulatory status of RAC and ZH, as well as the different effects they have on meat tenderness, can influence the choice of feedlot additives used by producers to optimize beef production and meet consumer demands.