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This study is a meta-analysis of the effects of the beta-agonists zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RAC) on feedlot performance, carcase characteristics of cattle and Warner Bratzler shear force (WBSF) of muscles. It was conducted to evaluate the effect of the use of these agents on beef production and meat quality and to provide data that would be useful in considerations on the effect of these agents on meat quality in Meat Standards Australia evaluations. We conducted a comprehensive literature search and study assessment using PubMed, Google Scholar, ScienceDirect, Scirus, and CAB and identification of other studies from reference lists in papers and searches. Searches were based on the key words: zilpaterol, zilmax, ractopamine, optaflexx, cattle and beef. Studies from theses obtained were included. Data were extracted from more than 50 comparisons for both agents and analysed using meta-analysis and meta-regression. Both agents markedly increased weight gain, hot carcase weight and longissimus muscle area and increased the efficiency of gain:feed. These effects were particularly large for ZH, however, fat thickness was decreased by ZH, but not RAC. Zilpaterol also markedly increased WBSF by 1.2 standard deviations and more than 0.8 kg, while RAC increased WBSF by 0.43 standard deviations and 0.2 kg. There is evidence in the ZH studies, in particular, of profound re-partitioning of nutrients from fat to protein depots. This work has provided critically needed information on the effects of ZH and RAC on production, efficiency and meat quality.

The addition of β-agonists, such as ractopamine hydrochloride (RH), increase carcass weight and leanness when fed to Holstein steers. The objective of this experiment was to determine the effects of RH (Actogain, Zoetis) on Slice Shear Force (SSF) tenderness within USDA Quality Grade in Holstein steers. Holstein steers (n = 417; initial BW = 442 + 33.1 kg) were used in a randomized complete block design where RH was fed for 3 durations (28, 35, or 42 d) at 3 doses (0, 300, or 400 mg.steer-1.d-1). After harvest, SSF was measured on two 3.8 cm thick steaks selected from each side and aged either 14 or 21 d postmortem. Steaks were assigned a USDA Quality Grade based on marbling score (799 to 600 = High Choice; 599 to 401 = Low Choice; and < 400 = Select), and within USDA Quality Grade steaks were categorized into 3 tenderness categories (< 15.3 kg = very tender; 15.4 to 19.9 = tender; > 20.0 kg = tough) based on SSF value. With increasing RH dose, there was a linear increase (P < 0.001) in ADG. In addition, steers fed increasing RH had heavier HCW (linear effect, P = 0.02) and greater (linear effect, P = 0.01) LM area. Within USDA High Choice and Low Choice carcasses, after 14-d aging there was a linear decrease (P < 0.03) in very tender steaks and a linear increase (P < 0.05) in tough steaks as RH increased. For USDA Select carcasses there was a tendency (P = 0.06) for a linear increase in the percentage of tender steaks as RH increased. Duration of feeding resulted in a quadratic response (P = 0.04) for tender steaks from carcasses in the USDA High Choice Quality Grade, with steers fed for 35 d having the lowest percentage of tender steaks. After 21-d aging, there was no effect (P > 0.12) of dose of RH on tenderness within USDA Quality Grade. While the addition of RH to the diet of Holstein steers improved HCW and LM area, RH decreased the percentage of very tender steaks at 14-d postmortem. However, after 21-d aging, dose of RH did not affect tenderness within USDA Quality Grade category. Overall, the addition of RH to the diet of Holstein steers increased BW gain, HCW, LM area, and carcass leanness. Negative effects of RH on tenderness can be mitigated by aging steaks for 21 d.

An abstract of a study by Carmichael et al determining if N retention was improved with supplemental Zn above NRC concentrations with or without ractopamine hydrochloride (RH) inclusion is presented. Using Proc Corr, Zn and N retention were found to be positively correlated (r = 0.48, P < 0.01). Average daily gain and G:F across the 86 d trial were increased in RAC vs NORAC (P < 0.01). Overall, SUPZN appears to improve N retention, suggesting that increasing dietary Zn may be important for cattle growth beyond that induced by RH.

A 42-d research study evaluated effects of feeding beef steers increasing levels of dietary Zn from Zn methionine (AAC-Zn; ZINPRO, Zinpro Corporation, Eden Prairie, MN) with or without supplemental Cu from Cu amino acid complex (AAC-Cu; Availa Cu, Zinpro Corp.) concurrently with ractopamine hydrochloride (RAC; Optaflexx, Elanco Animal Health, Greenfield, IN). One hundred-twenty steers (mean BW = 624 kg), < 50 d from projected harvest were randomized to three pens (40 steers/pen) equipped with GrowSafe Systems (Calgary AB, Canada) feed bunk technology. Each pen was assigned to one of three treatment diets: 1) basal finishing diet + 30 mg Zn/kg DM from AAC-Zn (CON); 2) basal finishing diet + 90 mg Zn/kg DM from AAC-Zn (AAC-Zn90); or 3) AAC-Zn90 diet + 10 mg Cu/kg DM from AAC-Cu (AAC-Zn/Cu). Following allocation to treatments, cattle were acclimated to pen cohorts and GrowSafe feed bunks for 7 days. All steers were fed 300 mg RAC·hd-1·d-1 starting 35 d prior to harvest. Individual feed intake measurements began with RAC feeding and continued for 35 d until cattle were shipped for harvest. Carcass data were collected from each steer. Data were analyzed with individual animal as the experimental unit using PROC MIXED and PROC GLIMMIX procedures of SAS 9.4 (SAS Institute, Cary, NC). Numerically AAC-Zn90 fed cattle had heavier carcass weights than CON and AAC-Zn/ Cu. Steers fed AAC-Zn90 had greater (P = 0.02) marbling scores compared to AAC-Zn/Cu. Steers fed AAC-Zn90 had lower backfat thickness (P = 0.02) and numerically greater marbling scores compared to CON. A biphasic program of feeding a lower level of AAC-Zn for the duration of the finishing phase followed by an increased rate of AAC-Zn during RAC feeding may optimize overall live and carcass response and improve total individual animal value.

This study evaluated the effect of trenbolone acetate + estradiol implants (TBA), melengestrol acetate (MGA), and ractopamine hydrochloride (RAC) on the performance of beef cattle fed barley grain/corn silage diets. Beef cattle (279 ± 10.1 kg) were used in a complete randomized 4-yr study (yr 1, 2, n = 120 heifers and 80 steers; yr 3, 4, n = 120 heifers and 120 steers). Cattle were blocked by weight and randomly assigned to 4 pens/treatment/yr. Treatments were 1) control heifers [no growth promoters (GP)], 2) TBA implanted heifers, 3) MGA heifers, 4) control steers (no GP), and 5) TBA implanted steers (yrs 1 to 4), and included a sixth treatment 6) TBA implanted + RAC steers for yrs 3 and 4. Cattle were fed for a similar duration (262 d ± 8) in all treatments. TBA increased the DMI of steers and heifers (P < 0.001) compared to controls (9.52 vs. 8.73 kg DM/d). MGA did not affect DMI (P = 0.41); however, TBA+RAC steers had grater DMI (P = 0.02; 9.91 vs. 9.58 kg DM/d) compared to TBA steers. Compared to controls, TBA heifers had greater ADG (P < 0.001; 1.45 vs. 1.29 kg), G:F (P < 0.001; 0.157 vs. 0.149), and carcass weight (P < 0.001; 390 vs. 360 kg). TBA also increased steers ADG (P < 0.001; 1.70 vs. 1.41 kg), G:F (P < 0.001; 0.174 vs. 0.161), and carcass weight (P < 0.001; 425 vs. 389 kg). Compared to control heifers, MGA increased (P < 0.01) ADG, G:F, and carcass weight by 8.1%, 7.0%, and 4.7%, respectively. The ADG and carcass weight of TBA+RAC steers increased (P < 0.01) by 5.6% and 3.2%, respectively with no effect (P = 0.87) on G:F compared to TBA steers. This 4-yr study demonstrates the consistent positive impact of conventional growth-enhancing technologies.

Two experiments were conducted to evaluate the effects of ractopamine hydrochloride (RAC) dose and duration on growth performance and carcass characteristics of finishing steers. In Exp. 1, 336 crossbred steers (initial BW of RAC feeding = 539 kg [SD 22]) were used in a 2 ... 2 factorial arrangement of treatments with one factor being RAC dose (0 or 200 mg/steer daily) and the other factor being RAC duration (28 or 42 d prior to harvest). There were no RAC dose ... duration interactions (P ≥ 0.08) for growth performance or carcass characteristics. Feeding 200 mg RAC/steer daily increased (P < 0.01) live final BW by 9.0 kg compared with steers not fed RAC. Carcass-adjusted final BW, ADG, and G:F were greater (P < 0.01) for steers fed 200 mg RAC/d compared with steers not fed RAC. Hot carcass weight was 4.7 kg heavier (P < 0.01) for steers fed 200 mg RAC/d compared with steers not fed RAC. In Exp. 2, crossbred steers (n = 576; experiment initial BW = 408 kg [SD 29]) were used in a randomized block design with a 3 ... 3 factorial arrangement of treatments. Factors included RAC dose (0, 300, and 400 mg/steer daily) and RAC duration (14, 28, or 42 d prior to harvest). There was a tendency (P ≤ 0.08) for an interaction of RAC dose ... duration for final live BW, DMI, and live G:F; therefore, simple effects are presented. At 28 d, live final BW for steers fed 400 mg RAC/d were heavier (P < 0.01) than for steers fed 0 mg RAC/d. There was a tendency at 28 d for increased live final BW for steers fed RAC at 300 mg/d (P = 0.08) compared with steers fed RAC at 0 mg and for steers fed 400 mg RAC/d compared with steers fed 300 mg RAC/d (P = 0.06). Live final BW was greater (P < 0.01) for steers fed RAC for 42 d at 300 and 400 mg/d compared with steers fed 0 mg; however, live final BW was similar (P = 0.48) between steers fed 300 and 400 mg RAC/d. Despite no RAC dose ... duration interaction (P = 0.30) for HCW, simple effects will be presented for consistency. Hot carcass weight was greater for steers fed 300 and 400 mg RAC/d for 28 and 42 d compared with steers fed 0 mg at 28 (P ≤ 0.02) and 42 d (P < 0.01). Feeding 300 mg RAC/d for 28 or 42 d increased HCW by 5.1 and 7.6 kg, respectively, compared with steers fed 0 mg RAC. Additionally, feeding 400 mg RAC/d for 28 or 42 d resulted in increases of 8.9 and 9.4 kg, respectively, in HCW compared with steers fed 0 mg RAC. In conclusion, our results confirm that feeding RAC improves growth performance and carcass weight, with an optimal duration of feeding RAC being 28 d.

Objective This work was carried out to evaluate the effects of zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RH) combined with immunocastration on the welfare traits of feedlot Nellore cattle. Methods Ninety-six Nellore males (average body weight [BW] = 409±50 kg; average 20 mo of age) were divided into two groups according to BW; half of the animals in each group received two doses of an immunocastration (ImC) vaccine in a 30 day interval, and the other half did not receive the vaccine (NoC). Afterward, the animals were housed and fed a common diet for 70 days. Then, they were split into three groups and fed one of the following diets for 30 additional days: control (CO) diet, with no β-AA; ZH diet, containing 80 mg/d ZH; and RH diet, containing 300 mg/d RH. Welfare traits were assessed by monitoring body surface temperature using infrared thermography (IRT) and plasma cortisol and temperament measurements. Results There was no interaction between sexual condition and diet for any trait. The ImC and NoC groups did not differ in rectal and ocular temperatures. The ImC animals had higher flight speeds (p = 0.022) and tended to have higher cortisol levels (p = 0.059) than the NoC animals. Animals fed ZH and RH did not differ in cortisol levels, respiratory rate, rectal temperature, temperature measured by IRT, or temperament behaviour. Conclusion The ImC animals showed a less stable temperament during handling practices than NoC, whereas ZH and RH supplementation had no adverse effects on animal welfare.

Abstract Ractopamine hydrochloride is a commercial beta-adrenergic agonist commonly used as a dietary supplement in cattle production for improved feed efficiency and growth promotion. Currently, regulatory target tissues (as approved in the New Animal Drug Application with Food and Drug Administration) for ractopamine residue testing are muscle and liver. However, other tissues have recently been subjected to testing in some export markets for U.S. beef, a clear disregard for scientific maximum residue limits associated with specific tissues. The overall goal of this study was to develop and validate an LC-MS/MS assay to determine whether detectable and quantifiable levels of ractopamine in digestive tract-derived edible offal items (i.e., abomasum, omasum, small intestine, and reticulum) of cattle resulted from tissue residues or residual ingesta contamination of exposed surfaces of tissues (rinsates). Tissue samples and corresponding rinsates from 10 animals were analyzed for parent and total ractopamine (tissue samples only). The lower limit of quantitation was between 0.03 and 0.66 ppb depending on the tissue type, and all tissue and rinsate samples tested had quantifiable concentrations of ractopamine. The highest concentrations of tissue-specific ractopamine metabolism (represented by higher total vs. parent ractopamine levels) were observed in liver and small intestine. Contamination from residual ingesta (represented by detectable ractopamine in rinsate samples) was only detected in small intestine, with a measured mean concentration of 19.72 ppb (±12.24 ppb). Taken together, these results underscore the importance of the production process and suggest that improvements may be needed to reduce the likelihood of contamination from residual ractopamine in digestive tract-derived edible offal tissues for market.