The Impact of Lubabegron Supplementation on Meat Quality of Feedlot Steers

Live animal production and product collection

The live animal management protocols are described in detail by Edmonds et al. (2024). Briefly, British and continental crossbred steers (N = 2,160), typical for US feedlots, were assigned to a 4 × 3 factorial arrangement comprised of 2 factors: dose (0, 1.5, 3.5, and 5.5 mg of EX/kg of dry matter [DM]) and duration (28, 56, or 84 d) in a completely randomized block design. Fifteen replicates of the 12 treatments were housed in pens of 12 steers each. The study was conducted in 5 cycles consisting of 3 blocks or 36 pens per cycle (a total of 180 pens). Cattle were transported to a commercial beef processing facility at the end of the finishing period. Three carcasses that graded (USDA) low choice were selected per pen to obtain a subset of carcasses. A total of 108 striploins were collected from the right side of each carcass during each kill cycle, resulting in a total of 540 striploins over the 5 cycles for further evaluation (lean color, muscle fiber typing, trained sensory panel evaluation, and shear force).

A 1.27-cm portion was obtained from the striploin at the harvest facility to represent day 0, and the remaining striploins were labeled, vacuum packaged, and shipped to Colorado State University (CSU) under refrigeration. Upon arrival at CSU, striploins were fabricated into five 6.35-cm sections and randomly assigned to a PM aging period of 7, 14, 21 or 28 d. After aging, each 6.35-cm section was fabricated into two 2.54-cm steaks and one 1.27-cm steak, vacuum packed, and placed into frozen storage. The 2.54-cm steaks were randomly assigned to either trained sensory panel evaluations or shear force analysis. While all the aging periods were used for shear force analysis, trained sensory panel evaluation was performed only on steaks aged for 14 d due to the large sample numbers.

Instrumental color

Objective lean color measurements were recorded immediately after carcass grade data were collected in the beef processing facility. Measurements were obtained by trained CSU personnel from the Longissimus lumborum, using a portable spectrophotometer (Illuminant A, 6-mm aperture, and 10° observer; Hunter MiniScan XE, Hunter Labs, Reston, VA) that was calibrated before each use (King et al., 2023). A total of 3 readings of CIE L* (lightness), a* (redness), and b* (yellowness) values for each steak were collected and averaged for each carcass.

Muscle fiber typing

A total of 96 strip steaks (8/treatment) were collected postgrading and immediately shipped to Kansas State University for muscle fiber typing and muscle fiber cross-sectional area (CSA) evaluation. Methods used by Ebarb et al. (2016) and Ebarb et al. (2017) were followed for immunohistochemical staining with slight modifications. Ten micrometer cryosections were blocked with phosphate-buffered saline (PBS) solution with 5% horse serum for 30 min. Cryosections were incubated for 1 h in a primary antibody solution containing antimyosin heavy chain type I (BAD.5, Developmental Studies Hybridoma Bank, University of Iowa, Iowa City, IA) hybridoma supernatant, antimyosin heavy chain all but IIX (BF-35, Developmental Studies Hybridoma Bank), and anti-α-dystrophin (Abcam, Cambridge, MA). After the first PBS washing step, cryosections were incubated in a secondary antibody solution containing AlexaFluor 488 (for BF-35 and BAD.5), 594 (for dystrophin), and 633 (for BAD.5; Invitrogen, San Diego, CA). After completion of the final PBS wash, an Eclipse TE 2000-U microscope (Nikon, Lewisville, TX) equipped with an X-cite 120 epifluorescence illumination system (EXFO, Ontario, Canada) was used in order to visualize slides. Photomicrographs were captured using a Photometrics Cool Snap EF digital camera (Nikon) and analyzed for individual muscle fiber CSA and myosin heavy chain isoforms using the NIS-Elements software (Nikon). Fibers costaining for BF-35 and BAD.5 were considered type I fibers, fibers staining positive for BF-25 but negative for BAD.5 were considered type IIA fibers, and fibers not staining positive for BF-35 and BAD.5 were considered to be type IIX fibers.

Trained sensory panel

The study was approved by the CSU Institutional Review Board (IRB#022-19H). The striploin steaks (n = 540) aged for 14 d were subjected to trained sensory panel evaluation. Steaks were randomly assigned to 1 of 45 panel sessions, with 12 steaks evaluated per panel. The steaks were also randomly assigned a serving order within each panel. Prior to trained panel evaluations, panelists were trained to evaluate a multitude of flavor attributes (beef flavor, fat-like, brown roasted), off flavors (bloody/serumy, metallic, oxidized, liver-like), basic tastes (sour, bitter, umami) as well as tenderness (initial, sustained, overall) and juiciness (initial, sustained, overall) on a 15-point line scale with 0.5 increments according to the American Meat Science Association sensory guidelines (Table 1). Each steak was evaluated by a trained sensory panel consisting of 6 personnel. Frozen steaks were tempered for 48 to 60 h at 0–2°C in order to attain a raw internal temperature of 0–4°C at the time of cooking.

Before cooking, all excess external fat was trimmed off, and weights were recorded in order to quantify cook loss. Cook loss was quantified (as a percentage) by subtracting the final-cook weight from the initial weight, followed by the division with the initial cook weight. Internal temperatures were measured using a calibrated type K thermocouple thermometer (AccuTuff 340, model 34040, Cooper-Atkins Corporation, Middlefield, CT) placed in the geometric center of each steak. Steaks were cooked in a combi-oven (Model SCC WE 61 E; Rational, Landsberg am Lech, Germany) until a peak internal temperature of approximately 71°C was achieved.

Postcooking, steaks were vacuum packaged and placed in a warm water bath at 55°C to maintain temperature throughout the panel. Cooked steaks were trimmed of all external fat and connective tissue and cut into 1-cm² cubed pieces, and 2–3 pieces were served to each panelist for evaluation. Panelists rated each steak for the following attributes: initial and sustained tenderness, overall tenderness, initial and sustained juiciness, overall juiciness, beef flavor, fat-like, brown roasted, bloody/serumy, metallic, oxidized, liver-like, sour, bitter, and umami (Table 1). Initial and sustained tenderness and juiciness values were averaged in order to obtain overall tenderness and juiciness scores.

Slice shear force and Warner-Bratzler shear force

Striploin steaks that represented each PM aging period (0, 7, 14, 21, 28 d) were randomly assigned to slice shear force (SSF) testing. Before cooking, all excess external fat was trimmed off, and the pre-and postcooking weights were recorded in order to quantify cook loss. The samples were cooked following the same procedures as described previously. Immediately postcooking, weights were recorded, and a 1-cm thick and 5-cm long slice was removed parallel to the longitudinal direction of the muscle fibers from the lateral portion (∼1/3) of the steak. This slice was sheared perpendicular to the muscle fibers using a universal testing machine (Instron Corp., Canton, MA) equipped with a flat, blunt-end blade (crosshead speed: 500 mm/min, load capacity: 100 kg) to measure SSF for each steak.

After SSF values were recorded, the remaining portions of the steak were allowed to cool to room temperature (22°C), and an average of 6 cores (1.2-cm in diameter) were removed from each steak parallel to muscle fiber orientation. Each core was sheared once, perpendicular to the muscle fiber orientation, using a universal testing machine (Instron Corp., Canton, MA) fitted with a Warner-Bratzler shear head (crosshead speed: 200 mm/min, load cell capacity: 100 kg). Peak shear force was recorded, and the values for each steak were averaged to obtain a single Warner-Bratzler shear force (WBSF) value.

Statistical analysis

Separate mixed models were used for color (L*, a*, b*, hue, chroma), muscle fiber type (type I, II, IIA, IIX, ICSA, IIACSA, IIXCSA), tenderness (WBSF, SSF), and trained sensory panel ratings (cooking loss, initial tenderness and juiciness, sustained tenderness and juiciness, overall tenderness, overall juiciness, beef flavor, umami, fat-like, bloody/serumy, brown roasted, metallic, oxidized, sour, liver-like, and bitter). Fixed effects for color and muscle fiber type included dose (0, 1.5, 3.5, 5.5 mg/kg of DM), feeding duration ([FD] 28, 56, 84 d), and the dose × FD interaction with the pen as a random effect. Fixed effects for the trained sensory panel included dose, FD, and the dose × FD interaction. Fixed effects of SSF and WBSF included dose, FD, PM aging periods (0, 7, 14, 21, 28 d), and their interactions. Additional random effects were included for tenderness (stripID) and trained sensory panel (session date and freeze date) to account for the design. For each response, treatments were compared using Tukey-adjusted (carcass characteristics, color, muscle fiber typing, tenderness) or Kenward-Roger-adjusted (trained sensory panel) pairwise comparisons. All striploins missing a value or a score were removed from the final analysis to ensure consistency. Analysis was conducted using RStudio (RStudio 1.1.463) using the lme4 (Bates et al., 2015), lmerTest (Kuznetsova et al., 2017), and emmeans (Lenth, 2019) packages with significance set at an α level of 0.05.

Instrumental color

There was no dose × FD interaction (P > 0.05) for any of the color attributes measured. Dose (P < 0.05) had a significant effect on a* (redness) and b* (yellowness) values (Figure 1), while it was not significant (P > 0.05) for L* (lightness) values. The EX supplementation at 3.5 mg/kg of DM or above resulted in slightly less a* and b* compared to the control, as indicated by the lower a* (P < 0.01) and b* (P < 0.01) values, respectively. In the current study, L* values did not differ between striploins obtained from EX-supplemented and nonsupplemented cattle (Table 2). Previous studies have suggested that RAC (Quinn et al., 2008; Woerner et al., 2011) supplementation has minimal impact on L*, a*, or b* values of beef steaks, while ZH (Rogers et al., 2010) supplementation had an impact on L*, a*, and b* values depending on FD. On the other hand, some studies indicated that b* values increased with RAC supplementation (Avendaño-Reyes et al., 2006), whereas b* values were not affected by ZH supplementation (Avendaño-Reyes et al., 2006; Garmyn et al., 2014).

Figure 1.

Least-squares means of a* and b* values of Longissimus lumborum muscle from cattle fed Experior (0, 1.5, 3.5, and 5.5 mg of Experior/kg of DM, dry matter) averaged over 3 feeding durations (28, 56, 84 d).

The hue angle is considered the intensity of color that corresponds to the vividness of a specific color (King et al., 2023) and was influenced (P < 0.05) by the FD (Table 2). Increasing FD from 28 to 84 d decreased (P < 0.05) the saturation of the lean color. Chroma is an important attribute in relation to fresh meat color and consumer acceptability (Holman et al., 2017) and was influenced (P < 0.05) by the dose. Striploins from nonsupplemented cattle had a greater (P < 0.01) saturation (chroma) when compared to all EX-supplemented cattle, except for 1.5 mg/kg of EX that was similar to the control (0 mg/kg of EX). Similarly, Martin et al. (2014) reported that the addition of ZH to the finishing diet of feedlot steers resulted in striploin steaks that were less red and less vivid (decreased saturation) than lean from both RAC supplemented and nonsupplemented cattle. Overall, even though there were minor statistical differences in the color of EX-supplemented cattle, it may not correspond to a biological significance, suggesting that there would not be a negative effect on consumer perception.

Muscle fiber typing

The percentage of type I, IIA, or IIX muscle fibers was not affected (P > 0.05) by the treatments (Table 3). Similarly, there was no impact (P > 0.05) of the dose or FD on the CSA for type I and type IIB muscle fibers. On the other hand, there was a dose × FD interaction (P < 0.05) for the CSA of muscle fiber type IIX (Table 4). The type IIX CSA were similar (P > 0.05) across all FD for muscle types produced from cattle fed 0, 1.5, and 3.5 mg of EX per kilogram of DM. However, the type IIX CSA decreased (P < 0.05) in cattle supplemented at 5.5 mg of EX per kilogram of DM for 56 or 85 d, with the smallest IIX CSA being from cattle that were fed the highest dose of EX for the longest duration (5.5 mg/kg of DM for 84 d). As EX dosage increased from 3.5 to 5.5 mg/kg of DM for 84 d, the type IIX CSA decreased (P < 0.05) from 5,177 to 3,907 μm.

Previous studies have demonstrated that cattle supplemented with RAC show a shift from fiber type I to fiber type II (Gonzalez et al., 2009). Moreover, supplementation with ZH resulted in an increase in the concentration of type IIX muscle fibers (Baxa et al., 2010). Additionally, Rathmann et al. (2009) indicated that type I muscle fibers were not altered with the supplementation of ZH, though a decrease in type IIA fiber was reported. In agreement with the results of the current study, type I and II muscle fiber CSA were not affected by the administration of RAC (Gonzalez et al., 2009). However, other research has demonstrated that ZH and RAC treatments can increase type IIX and IIA muscle fiber CSA, respectively, when supplemented along with a growth implant (Ebarb et al., 2016; Ebarb et al., 2017). On the other hand, Gonzalez et al. (2008) reported that RAC supplementation at 200 and 300/mg/hd/d resulted in an increase in the percentage of type I and IIA fibers. The differences in response between the current and previous studies could be due to the differences in the mode of action of the products tested (with EX being a β-adrenergic modulator), dose, and FD.

Trained sensory evaluation

Striploin steaks aged for 14 d PM were evaluated using trained sensory panelists, and the mean values for attributes measured are presented in Table 5. No interactions (P > 0.05) were observed for any of the attributes measured. However, the main effect of dose and duration was significant (P < 0.05) for some of the attributes (Table 5). The EX supplementation did not affect (P > 0.05) cook loss of the striploin steaks. Similar results were reported by Boler et al. (2012) when evaluating steaks from cattle supplemented with RAC. On the other hand, Garmyn et al. (2014) reported that βAA supplementation increased cook loss compared to control, particularly when steers were fed ZH.

Initial tenderness, sustained tenderness, overall tenderness, and initial and overall juiciness scores for steaks differed (P < 0.05) between control and EX-supplemented cattle regardless of the FD. Steaks associated with EX supplementation were slightly less tender and juicy (P < 0.05) than steaks from nonsupplemented cattle, although the differences might be too small to contribute to a biological significance. Similar results were reported by Gruber et al. (2008), Leheska et al. (2009), and Arp et al. (2013), with supplemented cattle producing steaks that were less tender than those from nonsupplemented cattle. Previously, Leheska et al. (2009) indicated that ZH supplementation decreased overall juiciness scores when FD extended from 20 to 40 d for steers or heifers. On the other hand, Garmyn et al. (2014) reported that ZH and RAC did not affect juiciness scores when compared to control steaks. Similarly, Arp et al. (2013) indicated that ZH and RAC did not affect juiciness scores when compared to control steaks.

The FD was significant (P < 0.05) for liver-like and bitterness flavors. When FD increased from 28 d to 56 d and 56 d to 84 d, panelists were less likely to detect the presence of liver-like flavors. Additionally, bitterness increased (P < 0.05) by 0.8 units as FD extended from 28 and 56 to 84 d. Leheska et al. (2009) reported that βAA supplementation decreased the prevalence of beef flavor in heifers as well as flavor intensity in both steers and heifers. However, in agreement with the current study, Arp et al. (2013) and Gruber et al. (2008) reported no difference in beef flavor with βAA supplementation. Overall, EX supplementation had minimal impact on the flavor evaluated using trained panelists after 14 d of aging, as indicated by the small numerical difference.

SSF and WBSF

There was no 3-way interaction (P = 0.21) between dose × FD × PM aging, as well as no interaction (P = 0.12) between dose × FD for SSF values. However, the dose × PM aging interaction (Table 6) and FD (Figure 2) were significant (P < 0.05). The control steaks had lower (P < 0.05) SSF than steaks from EX-supplemented cattle on day 0. Once steaks were aged for 14 d, all steaks associated with EX supplementation had similar (P > 0.05) SSF values (15.3, 16.3, and 15.8 kg), whereas the controls produced steaks that were more (P < 0.05) tender (13.5 kg). After 21 d aging, the control steaks were similar (P > 0.05) to steaks from cattle supplemented with 1.5 and 3.5 mg of EX per kilogram of DM. Additionally, by 28 d of aging, all steaks from supplemented and nonsupplemented cattle had similar (P > 0.05) SSF values. As FD increased from 28 d to 84 d, the SSF values increased (P < 0.05; Figure 2). However, cattle fed EX for 56 d had steaks with SSF values that were similar (P > 0.05) to those fed for 28 and 84 d.

Figure 2.

Least-squares means of Warner-Bratzler shear force and slice shear force values of Longissimus lumborum muscle from cattle fed Experior for 28, 56, or 84 d averaged over all doses (0, 1.5, 3.5, and 5.5 mg of Experior/kg of dry matter) and postmortem aging periods (0, 7, 14, 21, 28 d). FD, feeding duration.

There were no 3-way interactions (P = 0.91) between dose × FD × PM aging or 2-way interactions between dose × FD (P = 0.71) for WBSF. Similar to SSF, the dose × PM aging interaction was significant (P < 0.05; Table 7). The control steaks and steaks from steers fed 1.5 mg/kg of EX had similar (P > 0.05) WBSF values before aging. However, those steaks (0 and 1.5 mg/kg of EX) were more (P < 0.05) tender than those from steers fed 3.5 and 5.5 mg/kg of EX before PM aging. As expected, steaks from supplemented and nonsupplemented cattle aged for 28 d had lower (P < 0.05) WBSF values than those aged for 0, 7, and 14 d (Table 7). The main effect of FD was also significant (P < 0.05) for WBSF. The WBSF values increased (P < 0.05) by 0.26 kg when cattle were fed for the final 84 d compared to 28 d (Figure 2). However, WBSF values were similar (P > 0.05) for steaks from cattle fed for 28 d vs. 56 d and 56 d vs. 84 d. While the increase may have been statistically significant, there may not be a substantial biological difference in tenderness between the FD, as consumers might not be able to detect minor differences in tenderness (Miller et al., 2001).

The effect of βAA supplementation on the shear force of beef steaks has been investigated extensively. Previous research indicated that RAC supplementation at 200 mg/hd/d for the final 28 d of the finishing period resulted in Longissimus muscle steaks that were tougher than controls (Gruber et al., 2008). Garmyn et al. (2014) also reported that steaks from cattle supplemented with ZH were tougher than those fed either RAC or a control diet at 14 and 21 d of aging. These authors also observed that increasing PM aging from 14 to 21 d improved the proportion of steaks eligible to be labeled as certified tender and very tender. Similarly, Scramlin et al. (2010) indicated that WBSF values of steaks from RAC and ZH-supplemented cattle decreased with PM aging. When steers were supplemented with 8.33 mg/kg of ZH for the final 20, 30, and 40 d, the steaks from nonsupplemented cattle were more tender than the ZH-supplemented cattle (Rathmann et al., 2009). These authors also observed that as aging time increased from 7 to 21 d PM, the WBSF in the control steers decreased by only 0.42 kg; whereas, the ZH treatments (20, 30, and 40 d) recorded decreases of 0.89, 1.06, and 1.15 kg, respectively.

On the other hand, Quinn et al. (2008) reported similar WBSF values for control and RAC supplemented (200 mg/hd/d of RAC for 28 d of the finishing period) Longissimus muscle steaks after 14 d of aging. Similarly, Boler et al. (2012) reported similar WBSF values among striploins aged for 7, 14, and 21 d when steers were fed 200 mg/hd/d RAC compared with steers that were fed a controled diet. However, both striploin steaks from RAC (200 mg/hd/d) and control fed cattle were more tender than striploins aged for 7, 14, and 21 d from steers fed 300 mg/hd/d (Boler et al., 2012), indicating that dose could be a factor affecting shear force when βAA are used, similar to the results of the current study. Nevertheless, studies have indicated that when subjected to PM aging of 14 d or greater, the negative influence on tenderness associated with the feeding of βAA is greatly decreased (Scramlin et al., 2010; Boler et al., 2012). Arp et al. (2013) also reported that WBSF values were higher for steaks aged 14 d PM from ZH-supplemented steers when compared to control and RAC steaks. Overall, in agreement with the results of previous studies, the WBSF and SSF values for the steaks consistently decreased (or became more tender) as PM aging days increased in the current study.

The beef industry and the USDA have established thresholds for tenderness by considering categories such as very tender (WBSF < 3.9 kg; SSF < 15.4 kg) and tender (WBSF 4.4 kg; SSF 20.0 kg; ASTM, 2011). If a SSF value is less than 20.0 kg, the product is eligible to enter a “guaranteed tender” program (ASTM, 2011). In the current study, once 7 and 14 d of PM aging was reached, all treatment dosages were tender (15.3–20 kg), whereas the majority of steaks aged for 21 d would be eligible for a “certified very tender” (<15.3 kg) label claim.