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Journal of Animal Science - Animal Production

Effects of dietary ractopamine hydrochloride and zilpaterol hydrochloride supplementation on performance, carcass traits, and carcass cutability in beef steers1

 

This article in JAS

  1. Vol. 92 No. 2, p. 836-843
     
    Received: Sept 04, 2013
    Accepted: Dec 02, 2013
    Published: November 24, 2014


    3 Corresponding author(s): dale.woerner@colostate.edu
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doi:10.2527/jas.2013-7122
  1. T. S. Arp*22,
  2. S. T. Howard*,
  3. D. R. Woerner 3,
  4. J. A. Scanga,
  5. D. R. McKenna,
  6. W. H. Kolath,
  7. P. L. Chapman§,
  8. J. D. Tatum* and
  9. K. E. Belk*
  1. Center for Meat Safety and Quality, Colorado State University, Fort Collins 80523-1171
    Elanco Animal Health, Greenfield, IN 46140
    Cargill Meat Solutions Corporation, Wichita, KS 67202
    Department of Statistics, Colorado State University, Fort Collins 80523-1877

Abstract

British × Continental steers (initial BW = 484.6 kg) were fed at a commercial feed yard to evaluate the effects of β-agonists on live performance, carcass characteristics, and carcass subprimal yield. Weights and ultrasonic measurements were used to allocate steers to pens (n = 40) divided equally into 4 blocks, with 2 treatment replicates per block. Pens were randomly assigned to 1 of 5 treatments: control; ractopamine-HCl (RH) fed at 200 or 300 mg ∙ steer1 ∙ d1, or 400 mg ∙ steer1 ∙ d1 top dress for the final 30 d of feeding; or zilpaterol-HCl (ZH) fed at 7.5 mg/kg beginning 23 d before slaughter with a 3-d withdrawal period. Steers were harvested by block at a commercial facility over 4 wk. Carcass based performance measures were calculated using initial pen weights and actual DMI. From each pen, eight carcasses that were within ± 13.6 kg of the mean pen HCW were selected such that two carcasses were within each of the following four Yield Grade (YG) ranges: YG ≤ 2.8; 2.9–3.2; 3.3–3.5; YG > 3.5. Carcasses were fabricated by plant personnel to determine subprimal yield. Steers fed ZH had higher carcass-based ADG and carcass-based G:F compared with all other treatments (P < 0.05). Carcass-based ADG and carcass-based G:F were higher in RH treatments compared with controls (P < 0.05). Steers fed ZH had higher dressing percentages (1.0 to 1.6%) and larger LM area (4.3 to 6.7 cm2) than all other treatments (P < 0.05). Use of RH 400 and ZH increased HCW 6.3 and 11.1 kg, respectively compared with controls (P < 0.05). Compared with controls, RH 300 and ZH decreased marbling score and the frequency of carcasses qualifying for upper 2/3 Choice premiums (P < 0.05). Beta-agonists increased subprimal yield from the round and loin; however, blade meat was the only cut from the rib or chuck affected by β-agonists. Results from this study indicated improvements in performance and carcass traits as a result of β-agonist use; however, differences between ZH, RH 400, and RH 300 treatments were minimal for carcass traits and cutability. Increases in saleable yield following β-agonist use were not uniformly distributed across the four major primals and the majority of weight gain occurred in the lower priced cuts of the round and chuck. Increased response of the lower priced cuts to β-agonists could have economic implications to packers.



INTRODUCTION

The β-adrenergic agonists (βAA), ractopamine hydrochloride (RH; Optaflexx, Elanco Animal Health, Greenfield, IN), and zilpaterol hydrochloride (ZH; Zilmax, Merck Animal Health, Summit, NJ) are dietary supplements similar in function to naturally occurring catecholamines (Bell et al., 1998). Beta-agonists bind to G protein coupled receptors and cause cell signaling events that upregulate genes that cause protein accretion and downregulate genes that cause lipogenesis (Johnson, 2004). Ractopamine hydrochloride is a β1–AA that has been approved by the Food and Drug Administration (FDA) for use in swine and cattle. Zilpaterol hydrochloride is a β2–AA that has been approved for use in cattle only. Both commercially available βAA have been reported to improve feed efficiency, increase dressing percentage, and increase subprimal yield (Avendaño-Reyes et al., 2006; Elam et al., 2009; Hilton et al., 2009; Kellermeier et al., 2009; Rathmann et al., 2009; Garmyn et al., 2010; Hilton et al., 2010; Scramlin et al., 2010; Boler et al., 2012; Howard et al., 2014a, 2014b). Unfortunately, the benefits of βAA use occur at the expense of carcass quality and eating satisfaction; specifically, β-agonists tend to reduce marbling and tenderness (Avendaño-Reyes et al., 2006; Scramlin et al., 2010, Howard et al., 2014b).

Beta-adrenergic agonists appear to improve efficiency and yield while reducing eating quality. These effects necessitate evaluation of both commercially available βAA to quantify the costs and benefits to the beef industry. Unfortunately, few studies have compared the effects of RH and ZH in the same sample population (Avendaño-Reyes et al., 2006; Scramlin et al., 2010; Howard et al., 2014a) or evaluated all three levels of RH commonly fed to cattle (200, 300, and 400 mg ∙ steer–1 ∙ d–1). The objective of the current study was to determine the effect of RH at three different levels and ZH on live performance, carcass characteristics, and subprimal yield of beef steers.


MATERIALS AND METHODS

Animal handling protocols at the feedlot met the standards published in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999).

Cattle Receiving

Approximately 4,000 British × Continental crossbred steers from a commercial feeding facility in north Texas were used. Upon receiving at the feed yard, cattle were individually weighed, tagged with an electronic individual identification tag (EID), vaccinated with a modified live virus vaccine (Titanium 3, Agri Labratories, St. Joseph, MO) and a clostridial bacterin toxoid (Vision 7 with SPUR, Merck Animal Health, Summit, NJ), treated for internal parasites (Ivomec Plus, Merial, Duluth, GA), and treated metaphylactically with Micotil (Elanco Animal Health, Greenfield, IN). Steers were implanted with a Component TE-IS (16 mg estradiol and 20 mg trenbolone acetate; Elanco Animal Health, Greenfield, IN) or Ralgro (36 mg zeranol; Merck Animal Health, Summit, NJ) implant at initial processing depending on predicted terminal endpoint. Approximately 90 d before slaughter, steers were reimplanted with Component TE-S (24 mg estradiol and 120 mg trenbolone acetate; Elanco Animal Health, Greenfield, IN). Approximately 60 d before projected slaughter date, steers were transported to a separate research feed yard for the remainder of the trial.

Experimental Design and Treatments

Individual weights and ultrasonic carcass measurements were collected on arrival to research feed yard and used in a proprietary equation to determine projected terminal endpoint. Based on projected terminal endpoint, steers (mean BW = 484.6 ± 18.5 kg) were allocated into four blocks. Within each block, pens (n = 40) were randomly assigned to 1 of 5 treatment groups: a control that received implants, but no βAA (Control); RH fed at a rate of 200 mg ∙ steer1 ∙ d1 (RH 200) or 300 mg ∙ steer1 ∙ d1 (RH 300) for the final 30 d of the finishing period; RH fed as a top-dress at a rate of 400 mg ∙ steer1 ∙ d1 for the final 30 d of the finishing period (RH 400); or ZH fed at a rate of 7.5 mg/kg starting 23 d before slaughter with a 3 d withdrawal before slaughter. Within each block, each treatment was replicated twice.

Steers were immediately placed on a finishing ration after pen allocation. Diets were formulated to meet or exceed National Research Council (1996) requirements for growing–finishing beef cattle at the research feed yard’s feed mill. Basal diets were mixed daily at the feed yard. Ration components and nutrient composition are reported in Table 1. All cattle were fed their respective diets twice daily at 0700 and 1300 h. For RH treatments, a premix was included in the finishing ration to deliver 200 and 300 mg ∙ steer1 ∙ d1for the final 30 d of the finishing period. Cattle in the RH 400 treatment were fed a portion of the basal ration at initial feeding; the remainder of the basal ration was delivered 30 min later and was formulated to deliver 400 mg ∙ steer1 ∙ d1 of RH in an additional 2.5 kg ∙ steer1 of feed. Rumensin and Tylan (Elanco Animal Health, Greenfield, IN) were added to basal diets at 30.0 and 8.8 mg/kg DM, respectively. The top dress fed to the RH 400 treatment contained no Rumensin or Tylan. Diet samples were obtained directly from the feed bunks during the morning feeding. Steers in the ZH treatment received a targeted dose of 60 to 90 mg ∙ steer1 ∙ d1 which was delivered via a premixed ration that included ZH at a rate of 7.5 g/ton on a 100% DM basis. A portion of each sample was oven-dried at 100°C, composited and submitted to a commercial laboratory for analysis of RH and ZH inclusion rates.


View Full Table | Close Full ViewTable 1.

Dietary ingredients and chemical composition of basal finishing diet, DM basis

 
Item Value
Ingredient, %
    Flaked corn 39.45
    Corn silage 7.01
    Cotton seed hulls 2.50
    Sweet Bran Blend1 22.27
    Dried distillers grains 25.18
    Tallow 2.08
    Water 1.60
    Supplement2 0.0003
Chemical compositions3
    DM, % 73.92
    CP, % 16.94
    CF, % 21.14
    Fat, % 8.00
    NEm, Mcal/cwt 100.97
    NEg, Mcal/cwt 65.61
    Calcium, % 0.71
    Phosphorus, % 0.56
1Wet corn gluten feed.
2Rumensin and Tylan (Elanco Animal Health, Greenfield, IN) supplemented at 30.0 and 8.0 g/ton, respectively.
3Diets were formulated to meet or exceed all nutrient requirements of finishing steers (National Research Council, 1996).

Before initiation of the treatment phase, pen weights were collected in the morning before feeding for each treatment replicate between 0400 and 0700 h. Weights for all treatments were collected on the same day, thus pens fed ZH were weighed 8 d before treatment initiation. A weight was collected for each pen, after which steers were returned to their pens and their respective treatment was delivered. Initial weights and final weights recorded in this study were multiplied by 0.96 to adjust for a 4.0% shrink.

Slaughter and Carcass Data Collection

Steers were harvested by block on each Wednesday of four consecutive weeks. Final pen weights were collected the morning each block was shipped to slaughter. Steers were removed from feed for 24 h before harvest, weighed, and subsequently loaded on to 15.2 × 2.5 m pot-belly trailers for transport (<2 h) to the processing facility. Cattle were harvested using standard U.S. beef industry practices and under inspection by USDA-FSIS. Each pen was harvested consecutively and individual animal’s EID numbers were traced to an individual plant sequence number that was maintained throughout carcass data collection. Hot carcass weights were automatically recorded by the plant. During the final 2 wk of the project, mesenteric fat weights were collected from approximately fifty carcasses per pen. Mesenteric fat was removed by trained plant personnel, weighed by Colorado State University (CSU) personnel, and calculated as a percentage of hot carcass weight. Mesenteric fat weights were collected during the final 2 wk only due to availability of personnel to collect data. Carcasses were chilled for approximately 36 h before grading by USDA-Agricultural Marketing Service (AMS) personnel. Each carcass side was ribbed between the 12th and 13th rib by plant personnel and grading was conducted in accordance with USDA-AMS standards. Carcass data was collected from the in-plant video image analysis (VIA) instrument grading system (VBG 2000, E+V Technologies, Oranienburg, Germany).

Carcass Fabrication and Subprimal Yield

Carcasses of steers from each pen were subsampled for whole carcass fabrication to determine subprimal yield. Before grading, the mean HCW for each pen was calculated, and carcasses were identified that were ± 13.6 kg from the pen HCW mean. During grading, two carcass sides per pen that had been identified within the acceptable HCW weight range (±13.6 kg from the pen mean) were selected from each of four preliminary Yield Grade (YG) ranges: Lean (≤2.8), Low Average (2.9–3.2), High Average (3.3–3.5), and Fat (>3.5). Using this criterion, eight carcass sides per pen were used to represent each experimental unit. The selection criteria based on preliminary YG ensured equal representation of fat thickness common to industry within each treatment, and dictated that changes in muscle as a result of β-agonist use would be influential to differences in subprimal yield. Carcass sides were fabricated during a separate shift on Saturday of each week. Trained plant personnel fabricated carcass sides into cuts traditionally marketed by the facility and individual components were weighed and recorded by CSU personnel. Carcass sides included in the dataset had a weigh back yield (sum of all individual components) that did not exceed ±2% of the chilled side weight (CSW) that was collected immediately before fabrication.

Statistical Analysis

All performance variables are reported as carcass-based performance measures (Tatum et al., 2012). A beginning HCW was calculated from the initial weights taken on the day of treatment initiation. Carcass-based ADG and G:F were calculated for the final 30 d of the finishing period. Actual DMI was used to calculate G:F. For subprimal yield data, any carcass side that had a subprimal yield that exceeded the ±2% of the initial CSW were removed from the dataset before analysis. Subprimal yield was calculated as a percentage of CSW.

Plots of residuals and the W-statistic (Shapiro and Wilk, 1965) were evaluated to determine homogeneity of variance and normality for all data. Denominator degrees of freedom were calculated using the Kenward-Roger approximation (Kenward and Roger, 1997) and means were separated using pairwise t tests and a significance level of 0.05. SAS 9.3 (SAS Inst. Inc., Cary, NC) was used for all data analysis. Mixed models were analyzed using the MIXED procedure. Cutout data were analyzed using a mixed model that included random block and fabrication day effects. Models also included a random pen level error term for testing treatment effects.


RESULTS AND DISCUSSION

Performance and Carcass Characteristics

Performance and carcass data are summarized in Table 2. Steers fed RH 300 and RH 400 did not differ for any performance, Quality Grade, or YG response variables (P > 0.05). Estimated initial HCW did not differ by treatment (P = 0.9169); however, actual HCW differed by treatment (P < 0.05). Steers fed ZH had higher carcass-based ADG and G:F than any other treatment (P < 0.05). Advantages in carcass-based G:F found in cattle fed βAA resulted from improved carcass-based ADG and a trend for reduced DMI (P = 0.0575) compared controls. Dressing percentage was approximately 1% higher in cattle fed ZH compared with all other treatments (P < 0.05). Increased doses (RH 300 and RH 400) and potency (ZH) of βAA increased HCW by 4 to 12 kg compared with controls (P < 0.05). Studies that have evaluated performance on a live-basis have also reported higher growth and feed efficiency in cattle fed βAA (Schroeder et al., 2005; Avendaño-Reyes et al., 2006; Gruber et al., 2007; Elam et al., 2009; Scramlin et al., 2010; Boler et al., 2012).


View Full Table | Close Full ViewTable 2.

Effect of ractopamine hydrochloride (RH) and zilpaterol hydrochloride (ZH) on carcass characteristics of conventional beef-type steers

 
Item2 Treatment1
SEM P < FTRT3
Control RH 200 RH 300 RH 400 ZH
Initial HCW4 336.8 335.0 334.3 335.7 335.6 1.9 0.9169
Carcass ADG4 1.26d 1.37c 1.54b 1.57b 1.74a 0.04 <0.0001
DMI 9.89 9.60 9.73 9.83 9.63 0.13 0.0575
Carcass G:F4 0.13d 0.14c 0.16b 0.16b 0.18a 0.01 <0.0001
HCW, kg 376.6d 376.0cd 380.5bc 382.9ab 387.7a 1.9 0.0002
Dressing % 63.8bc 63.6c 64.2b 64.2b 65.2a 0.1 <0.0001
Mesenteric Fat, % 1.7 1.6 1.6 1.6 1.5 0.1 0.8429
LM area, cm2 84.7c 84.9c 86.3bc 87.1b 91.4a 0.7 <0.0001
12-rib fat, cm 1.1 1.1 1.1 1.1 1.1 0.1 0.8631
USDA yield grade 3.0a 3.0a 2.9a 2.9a 2.7b 0.1 0.0379
Marbling score5 429a 416ab 412b 420ab 408b 5 0.0422
a–dLeast squares means within a row lacking a common letter superscript differ (P < 0.05).
1Treatments: Control; RH = ractopamine hydrochloride (Elanco Animal Health, Greenfield, IN) fed at 200 or 300 mg ∙ steer–1 ∙ d–1 or 400 mg ∙ steer–1 ∙ d–1 top dress; ZH = zilpaterol hydrochloride (Merck Animal Health, Summit, NJ) fed at 6.8 g/ton.
2Pen used as experimental unit for statistical analysis.
3FTRT = Probability of difference between treatment means occurring when, in fact, no difference existed.
4Initial HCW = 0.2598 × (Initial BW × 0.04)1.1378; Carcass ADG = (Final HCW – Initial HCW)/Days on feed; calculated for final 30 d of finishing period; Carcass G:F = Carcass ADG/DMI; calculated for final 30 d of finishing period (Tatum et al., 2012).
5Marbling score: 400 = Small00.

When performance was expressed by carcass-based values, differences between steers receiving dietary RH and ZH supplementation were magnified since carcass weight gain outpaced live weight gain during the final weeks on feed in cattle fed ZH. Consequently, carcass-based measures of performance also help to explain increased dressing percentages reported following βAA use (Avendaño-Reyes et al., 2006; Scramlin et al., 2010; Howard, 2013). Current theories suggest a shift in protein metabolism from noncarcass components (e.g., kidney, pelvic, heart fat, organ weight, mesenteric fat, and hide weight) to carcass components. To attempt to explain this effect, mesenteric fat was weighed; however, no differences in weight of mesenteric fat between treatments were found (P = 0.8429). McEvers et al. (2013) summarized that calf-fed Holstein steers fed ZH had a lower percentage of empty body weight comprised of hide, liver, kidney, and empty gastrointestinal tract compared with controls. The findings of McEvers et al. (2013) may explain the increase in dressing percentage when live weight has been found to be relatively constant between cattle supplemented with ZH and controls.

Longissimus muscle area differed due to treatment (P < 0.05); however, subcutaneous fat opposite the LM (FT) did not (P > 0.05). These findings differ from those of Avendaño-Reyes et al. (2006), Scramlin et al. (2010), and Howard (2013), who reported FT was lower in cattle fed ZH. Zilpaterol hydrochloride and RH 400 increased LM area 6.6 cm2 and 2.4 cm2, respectively. Zilpaterol hydrochloride increased LM area by approximately 7%, which was greater than the observed increase in HCW (approx. 3%). Consequently, steers fed ZH had lower numeric YG compared with all other treatments (P < 0.05). Steers fed ZH had an increased frequency of YG1 carcasses and a reduced frequency of YG3 carcasses (P < 0.05; Table 3). No differences were found between RH treatments and controls for YG frequency data (Table 3).


View Full Table | Close Full ViewTable 3.

Effect of ractopamine hydrochloride (RH) and zilpaterol hydrochloride (ZH) on Quality Grade and Yield Grade distribution of carcasses from conventional beef-type steers

 
Item, %2 Treatment1
SEM P < FTRT3
Control RH 200 RH 300 RH 400 ZH
Prime 0.4 0.1 0.5 0.3 0.1 0.2 0.6762
Upper 2/3 Choice 13.7a 11.5ab 8.7b 11.8ab 3.1c 1.2 <0.0001
Choice 57.6 51.8 48.7 52.6 46.9 2.8 0.0973
Select 40.2 45.6 48.9 45.2 50.4 2.7 0.1076
No roll 1.3 2.0 1.8 1.3 1.8 0.4 0.6890
Hard bone 0.5 0.4 0.1 0.7 0.8 0.3 0.4555
Heavy HCW
        >430.9 kg 0.5 0.3 0.9 1.2 1.3 0.5 0.4448
    >    476.3 kg 0.0 0.0 0.1 0.1 0.1 0.1 0.7283
    Yield Grade 1 6.4b 5.6b 6.3b 6.3b 11.9a 1.6 0.0497
    Yield Grade 2 43.2 44.1 42.7 44.9 52.9 3.5 0.2332
    Yield Grade 3 43.7a 44.6a 46.2a 44.6a 31.9b 3.4 0.0397
    Yield Grade 4 6.6 5.7 4.7 4.2 3.3 1.4 0.4863
    Yield Grade 5 0.1 0.1 0.0 0.0 0.0 0.1 0.5799
a–cLeast squares means within a row lacking a common letter superscript differ (P < 0.05).
1Treatments: Control; RH = ractopamine hydrochloride (Elanco Animal Health, Greenfield, IN) fed at 200 or 300 mg ∙ steer–1 ∙ d–1 or 400 mg ∙ steer–1 ∙ d–1 top dress; ZH = zilpaterol hydrochloride (Merck Animal Health, Summit, NJ) fed at 6.8 g/ton.
2Pen used as experimental unit for statistical analysis.
3FTRT = Probability of difference between treatment means occurring when, in fact, no difference existed.

Marbling score differed by treatment (P < 0.05; Table 2) and was lower for steers fed ZH and RH 300 compared with controls (P < 0.05). The frequency of carcasses graded in the upper two-thirds of USDA Choice was decreased due to treatment (P < 0.05; Table 3) and there was a tendency for the frequency of carcasses graded USDA Choice to decrease due to treatment (P = 0.0973; Table 3). No differences were found between RH treatments for marbling score or Quality Grade frequencies, and there was no difference in marbling score between all RH treatments and steers fed ZH (P > 0.05). Multiple studies have reported no difference in marbling score of carcasses from cattle fed RH (Boler et al., 2012; Gruber et al., 2007; Howard et al., 2014a); however, Vogel et al. (2009) reported reduced marbling score and frequency of carcasses graded USDA Prime and Choice from Holstein steers fed RH. Studies that have evaluated the effect of ZH on USDA Quality Grade have reported lower marbling scores and a higher frequency of carcasses grading USDA Select in cattle fed ZH at comparable levels to those used in this work (Howard, 2013), and also at higher levels of ZH supplementation (Beckett et al., 2009; Elam et al., 2009; Montgomery et al., 2009).

Carcass Subprimal Yield

Effects of βAA on subprimal yields are reported in Table 4. Whole-muscle subprimal yield differed by treatment (P < 0.05) and was higher for steers fed ZH and RH 400 compared with controls and those fed RH 200. No differences were found in whole-muscle subprimal yield between any of the RH treatments; however, subprimal yield of steers fed RH 300 tended to be lower than those fed ZH (P = 0.08). Of the increased weight of total whole-muscle saleable yield in steers fed βAA, 65 to 74% occurred in the chuck and round (Fig. 1). More specifically, of the total saleable yield, βAA shifted the percentage accounted for by the major primals from the forequarter to the hindquarter (Fig. 2). Beta-agonists only tended to have an effect on proportion of CSW made up of muscles of the chuck; however, higher doses and potencies increased percentage of CSW comprised of the inside round, eye of round, outside round, strip loin, tri-tip, and quadriceps (P < 0.05). Percentages of CSW comprised of those subprimals affected by βAA were not different between steers fed RH 400 and ZH, except for the inside round. Steers managed as controls and those fed RH 200 did not differ in percentage of CSW comprised of any subprimal cut.


View Full Table | Close Full ViewTable 4.

Effect of ractopamine hydrochloride (RH) and zilpaterol hydrochloride (ZH) on subprimal yield of carcasses from conventional beef-type steers. Value presented as change from control

 
Item2 Treatment1
SEM P < FTRT3
Control RH 200 RH 300 RH 400 ZH
Chuck roll 0.00 −0.05 −0.05 −0.03 −0.06 0.07 0.9583
Chuck mock tender 0.00 0.02 0.02 0.03 0.04 0.01 0.1001
Chuck flat 0.00 0.00 0.00 −0.02 −0.02 0.01 0.3598
1 piece shoulder clod 0.00 0.07 0.05 0.09 0.14 0.04 0.1093
Teres major 0.00 0.00 0.01 0.01 0.01 0.00 0.1810
Pectoral muscle 0.00 0.03 0.04 0.01 0.02 0.02 0.4023
Bnls chuck short ribs 0.00 0.01 0.00 0.00 0.00 0.01 0.8858
Ribeye roll 0.00 −0.04 −0.06 −0.01 −0.04 0.03 0.5701
Brisket, boneless 0.00 −0.02 −0.02 0.07 0.11 0.05 0.1752
Back ribs 0.00 −0.02 −0.03 −0.02 −0.04 0.01 0.1711
Inside round 0.00d 0.05cd 0.19ab 0.15bc 0.28a 0.05 0.0012
Eye of round 0.00c 0.03bc 0.10ab 0.08a 0.12a 0.02 0.0005
Shank meat 0.00b 0.02ab 0.04a 0.01ab 0.04a 0.01 0.0145
Knuckle, peeled 0.00b 0.01b 0.13a 0.08ab 0.10a 0.03 0.0474
Outside (flat) round 0.00c 0.04bc 0.17a 0.10ab 0.17a 0.03 0.0001
Tenderloin 0.00 0.01 0.03 0.06 0.06 0.02 0.0526
Strip loin 0.00b 0.10a 0.06ab 0.07a 0.10a 0.03 0.0495
Top butt 0.00 −0.01 0.02 0.01 0.03 0.03 0.8017
Short rib 0.00 −0.01 0.01 −0.02 −0.02 0.01 0.2543
Flank 0.00 0.01 0.01 0.01 0.02 0.01 0.5559
Inside skirt 0.00 0.00 0.00 0.01 0.01 0.01 0.9578
Outside skirt 0.00 0.01 0.00 0.00 −0.01 0.01 0.3430
Sirloin flap 0.00 0.04 0.02 0.04 0.02 0.02 0.4038
Tri-tip 0.00b 0.02a 0.03a 0.02ab 0.05a 0.01 0.0221
Ball-tip 0.00 0.00 −0.02 0.01 0.04 0.03 0.6262
Blade meat 0.00b 0.00b 0.02b 0.04ab 0.08a 0.02 0.0255
Quadriceps 0.00c 0.01bc 0.11abc 0.08ab 0.14a 0.03 0.0021
50’s trim 0.00 −0.11 −0.10 −0.09 −0.13 0.05 0.3838
65’s trim 0.00 0.04 −0.02 0.06 0.01 0.05 0.8100
81’s trim 0.00 0.18 0.05 0.08 0.11 0.06 0.2938
86’s trim 0.00 0.04 0.10 0.05 0.10 0.03 0.0543
91’s trim 0.00a −0.06ab −0.02a −0.14b −0.10ab 0.03 0.0174
Trim 0.00 0.10 0.02 −0.03 −0.01 0.14 0.8618
Fat 0.00 −0.16 −0.42 −0.55 −0.53 0.24 0.4175
100% lean trim4 0.00 0.37 0.30 0.31 0.36 0.01 0.6243
Bone 0.00a −0.30ab −0.17a −0.23a −0.65b 0.12 0.0091
Whole muscle yield 0.00c 0.32bc 0.53abc 0.73ab 1.18a 0.46 0.0341
a–dLeast squares means within a row lacking a common letter superscript differ (P < 0.05).
1Treatments: Control; RH = ractopamine hydrochloride (Elanco Animal Health, Greenfield, IN) fed at 200 or 300 mg ∙ steer–1 ∙ d–1 or 400 mg ∙ steer–1 ∙ d–1 top dress; ZH = zilpaterol hydrochloride (Merck Animal Health, Summit, NJ) fed at 6.8 g/ton.
2Weight expressed as a percentage of chilled side weight; subprimals cut to plant specification. Pen used as the experimental unit for statistical analysis.
3FTRT = Probability of difference between treatment means occurring when, in fact, no difference existed.
4100% lean trim = (individual trim and fat components × % lean)/chilled side weight. Percentage lean calculated on individual trim and fat components based on output from a MeatMaster (FOSS, Hilleroed, Denmark).
Figure 1.
Figure 1.

Distribution of whole-muscle saleable yield added from control by primal from carcasses of conventional beef-type steers managed with or without supplementation in the diet with β-agonists. Control = Implant; RH 200 = Implant + ractopamine hydrochloride (RH; Elanco Animal Health, Greenfield, IN) at 200 mg ∙ steer–1 ∙ d–1; RH 300 = Implant + RH at 300 mg ∙ steer–1 ∙ d–1; RH 400 = Implant + RH at 400 mg ∙ steer–1 ∙ d–1; ZH = Implant + zilpaterol hydrochloride at 6.8 g/t.

 
Figure 2.
Figure 2.

Change from Control in distribution of total saleable yield comprised of whole-muscle cuts from each primal of conventional beef-type steers managed with or without supplementation in the diet with β-agonists. Control = Implant; RH 200 = Implant + ractopamine hydrochloride (RH; Elanco Animal Health, Greenfield, IN) at 200 mg ∙ steer–1 ∙ d–1; RH 300 = Implant + RH at 300 mg ∙ steer–1 ∙ d–1; RH 400 = Implant + RH at 400 mg ∙ steer–1 ∙ d–1; ZH = Implant + zilpaterol hydrochloride at 6.8 g/t.

 

Studies that have evaluated the effects of ZH on subprimal yield have reported the greatest changes in percentage of CSW comprised of individual subprimals occur in muscles of the round (Hilton et al., 2009; Kellermeier et al., 2009; Rathmann et al., 2009; Howard et al., 2014a). Howard et al. (2014a) summarized fundamental changes in muscle development occurred in calf-fed Holstein steers fed βAA. Our results are similar to the findings of Howard et al. (2014a) in that the majority of subprimal weight gain occurred in the low priced cuts of the round and chuck; however, our results differ from those of Howard et al. (2014a) as the proportion of total saleable yield found in the round and loin did not increase in a linear fashion as dose and potency of βAA increased (Fig. 2). Although distribution of total saleable yield was shifted from the forequarter to the hindquarter, a lower percentage of total saleable yield was shifted to the loin in steers fed RH 400 and ZH treatments compared with RH 300 and RH 200 (Fig. 2). This contrasts the findings of Howard et al. (2014a) who reported increased proportions of total saleable yield found in the loin when RH 400 and ZH were fed to calf-fed Holstein steers. This could indicate a differential response to βAA based on breed-type which was discussed in detail by Howard et al. (2014a).

Howard et al. (2014a) noted that if the majority of weight gain occurs in the lower priced cuts, then the value of βAA to packers may be due to reduced fat and increased absolute weight. Our findings partially support this claim in that absolute weight of subprimals was increased as a result of βAA use; however, fat was not different between any treatments in this study. Also, on a 100% lean basis, trim yields did not differ by treatment (P > 0.05). The selection criterion used in this study differed from the totally random selection used by Howard et al. (2014a), and the sample population was also inherently very lean based on estimates of FT and YG by treatment. Consequently, the results of this study may not be entirely indicative of differences in fat content that might be found between cattle fed different doses and potencies of βAA.

Rathmann et al. (2009) and Howard et al. (2014a) reported more pronounced effects of ZH supplementation on subprimal yield in the chuck, with an increased percentage of CSW found in the shoulder clod, shoulder tender, and mock tender. The current work did not find differences in percentage of CSW comprised of muscles of the chuck. In comparison with other studies that have evaluated subprimal yield of cattle fed βAA, the current study performed carcass fabrication in a large scale production facility at faster line speeds than a university meat laboratory. In this work, subprimals were cut to plant specifications rather than those published by the North American Meat Association or as International Meat Purchasing Specifications. Consequently, differences in subprimal yield could be partially attributed to different cut specifications. Additionally, Rathmann et al. (2009), Hilton et al. (2009), and Kellermeier et al. (2009) preselected cattle and carcasses to represent uniform YG parameters. The current study utilized selection criterion that sorted carcasses into four different fat thickness groups, which was also different from the random selection criteria used by Howard et al. (2014a).

Beta-agonists increased carcass-based measures of performance and tended to decrease DMI. Dressing percentage increased in steers fed βAA due to increased HCW that resulted from increased musculature in the round and loin. Advantages in performance and yield coincided with reduced marbling and percentage of carcasses graded in the upper two-thirds of USDA Choice. Beta-agonists increased subprimal yield; however, increases in saleable yield were not uniformly distributed across the four major primals. The majority of weight gain occurred in the chuck and round. Distribution of total saleable yield among the middle meats was virtually offset between controls and βAA treatments. A lower percentage of the total saleable yield of the carcass was found in the rib of cattle fed βAA, compared with a slightly higher percentage in the loin. Percentage bone was reduced in steers fed βAA, but no differences were observed in percentage fat. Beta-agonists offer advantages to packers through increased absolute weight of subprimal cuts; however, these gains are primarily realized in the lower priced cuts of the carcass. These advantages are likely not passed on to the retailer or the consumer who are simply asked to pay more for heavier subprimal and retail cuts.

 

References

Footnotes


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