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J. Anim Sci. 2007. 85:2019-2030. doi:10.2527/jas.2007-0004
© 2007 American Society of Animal Science
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ANIMAL PRODUCTS

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness1

B. A. Schneider*, J. D. Tatum*,2, T. E. Engle* and T. C. Bryant{dagger}

* Department of Animal Sciences, Colorado State University, Fort Collins 80523; and and {dagger} Five Rivers Cattle Feeding, Loveland, CO 80538


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW ≥ 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-ß (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.

Key Words: carcass • grade • growth promoter • heifer • tenderness


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
Conventional US beef production systems involve the use of anabolic implants during 1 or more phases of cattle production before slaughter. Although the use of anabolic implants is extremely effective for improving growth performance and profitability of growing and finishing cattle (Duckett and Andrae, 2001Go), research has shown that certain implant programs for finishing cattle can adversely affect product tenderness (Samber et al., 1996Go; Foutz et al., 1997Go; Platter et al., 2003bGo) and consumer acceptability (Roeber et al., 2000Go; Platter et al., 2003bGo).

Most previous investigations of the effects of hormonal implants on beef tenderness have involved steers. To date, only 3 studies have compared tenderness, measured using Warner-Bratzler shear force (WBSF), of beef produced by implanted vs. nonimplanted heifers (Crouse et al., 1987Go; Nichols et al., 1996Go; Kerth et al., 2003Go). Collectively, these studies involved 11 direct WBSF comparisons between implanted and nonimplanted heifers. Of these 11 comparisons, 2 suggested that implanting significantly increased WBSF (i.e., decreased tenderness), 8 showed no effect of implanting on WBSF, and 1 demonstrated a significant decrease in WBSF (i.e., increased tenderness) due to implanting. These results seem to suggest that, among heifers, anabolic implants have little or no effect on tenderness. However, existing information is simply too limited to support any valid inferences concerning the effects of heifer implant programs on beef tenderness.

Therefore, the objective of this study was to determine the effects of 11 different heifer finishing implant programs involving implant products containing different dosages of trenbolone acetate (TBA) and estradiol 17-ß (E2), administered either once or twice during finishing, on LM tenderness and beef carcass characteristics.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 LITERATURE CITED
 
Animals and Experimental Treatments
The Colorado State University Animal Care and Use Committee approved all experimental procedures involving live cattle. Five hundred Continental x British crossbred heifers (mean BW = 348 kg; SD ± 31.25 kg), projected to require approximately 140 d on feed before slaughter, were obtained from a single backgrounding operation in western Nebraska and transported to a large commercial cattle feedlot in north central Colorado. Upon arrival at the feedlot (June 6, 2005), heifers were given ad libitum access to water and a receiving diet for a period of 5 d before processing. During subsequent processing, each animal was weighed individually (initial BW), tagged with 2 uniquely numbered ear tags, and vaccinated for infectious bovine rhinotracheitis virus and bovine viral diarrhea virus types I and II (Titanium 3, Agri Laboratories Ltd., St. Joseph, MO).

Before leaving the processing chute, each heifer was allocated to 1 of 2 blocks based on initial BW (block 1, BW ≥ 340 kg; block 2, BW < 340 kg) and then was assigned randomly to 1 of 12 experimental treatments. Treatment groups included a nonimplanted, negative control and 11 implant treatments, which were chosen specifically to deliver cumulative dosages of TBA or E2, or both, ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 (Finaplix-H, Revalor-IH, Revalor-H, and Revalor 200, Intervet Inc., Millsboro, DE) during the finishing period (Table 1Go). Heifers assigned to the 11 implant treatments received their respective initial implants before leaving the processing chute. The implants were administered s.c. in the middle one-third of the ear using industry-recommended procedures for proper implant placement and sanitation of the implant site and implant applicator needles (Zero Defect Implanting, Vetlife Inc., Des Moines, IA). The same member of the feedlot processing crew administered implants throughout the course of the study.


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  		Table 1. Experimental design outlining the number of heifers in each treatment group, the frequency of implants administered during finishing, and the dosage rates (mg) of estradiol 17-ß (E2) and trenbolone acetate (TBA) received by heifers in each treatment group
 
Immediately after the initial processing, the heifers were sorted into 2 finishing pens according to block assignment. Heifers comprising each of the 2 blocks were penned and fed together. For this study, animal (rather than pen) served as the experimental unit. Correspondingly, heifers representing all 12 experimental treatments were commingled and fed together in each pen (block). Because the heifers were assigned to treatments randomly as they were moved through the processing facility, the numbers of heifers representing each treatment were not balanced between pens or within each pen.

Cattle Management
Cattle management practices (i.e., diets, health programs, and marketing dates) were specified by the feedlot management staff and were not modified for the experiment. Diets were formulated to meet or exceed NRC nutrient requirements for growing and finishing cattle (NRC, 2000Go). The finishing diet consisted of 74.74% steam-flaked corn, 9.34% corn silage, 7.30% dried distillers grain, 5.66% liquid supplement, and 2.96% tallow (DM basis) that was formulated to contain 13.43% CP and was dispensed 3 times daily to provide the heifers with ad libitum access to feed. Rumensin and Tylan (Elanco Animal Health, Greenfield, IN) were mixed in the diet at inclusion rates of 360 mg·animal–1·d–1 and 90 mg·animal–1·d–1, respectively, and melengestrol acetate (MGA; Upjohn Pharmacia, Kalamazoo, MI) was fed in the final ration at an inclusion rate of 0.5 mg·animal–1·d–1. Eighty-five days before slaughter, all heifers received a booster vaccination for infectious bovine rhinotracheitis and bovine viral diarrhea virus types I and II (Titanium 3, Agri Laboratories Ltd.), and heifers scheduled to receive a second implant were administered the appropriate implant (Table 1Go). Finished heifers were delivered for slaughter after 135 and 149 d on feed for block 1 and block 2, respectively. Due to concerns about carcass bruising and the possibility of increasing the incidence of dark cutting carcasses, the commercial cooperator, who owned the heifers, did not permit collection of individual final BW.

Slaughter, Carcass Data Collection, and Sampling Methods
On each delivery date (October 19 and November 1 for blocks 1 and 2, respectively), the heifers were transported approximately 25 km to a commercial beef-packing plant where they were slaughtered using conventional humane procedures. The identity of each animal was maintained throughout the slaughter process to facilitate collection of individual carcass-grade data. At the completion of the slaughter process, each carcass passed through 4 zones of electrical stimulation: 1) 16 V, 60 Hz, 15 s (1 s on, 1 s off); 2) 20 V, 60 Hz, 15 s (1 s on, 1 s off); 3) 24 V, 60 Hz, 20 s (1 s on, 1 s off); and 4) 28 V, 60 Hz, 13 s (2 s on, 1 s off). Carcasses then were chilled (at 2°C) for approximately 48 h. The chill routine involved intermittent spraying (2 min on, 8 min off) with a fine mist of 2°C water for the first 8 h. After the carcass-chilling period, a grading supervisor (USDA-Agricultural Marketing Service) assigned scores for marbling, skeletal maturity, and lean maturity and recorded the incidence and severity of lean quality defects (i.e., dark cutting characteristics and blood splash). In addition, experienced evaluators (Colorado State University personnel) recorded values for HCW, fat thickness, adjusted fat thickness, LM area, and percentage of KPH.

After collection of the carcass data, carcasses were fabricated, and strip loins (IMPS 180; USDA, 1996Go) were collected from the right sides of the 500 carcasses and immediately transported, under refrigeration, to the Meat Laboratory at Colorado State University. Each strip loin was divided into 5 sections (each 5.5-cm wide) that were removed sequentially beginning at the cranial end of the loin. Sections from each loin were assigned randomly to 1 of 5 postmortem aging treatments (3, 7, 14, 21, or 28 d), individually vacuum-packaged, aged for the appropriate period at 2°C, and then placed in frozen storage (–20°C). Frozen samples were cut into 2.54-cm-thick steaks using a band saw (model 400, AEW Thurne Inc., Norwich, UK). Individual steaks were vacuum-packaged, immediately returned to the freezer, and stored at –20°C for approximately 50 d until WBSF analysis was conducted.

Tenderness Measurements
Frozen steaks were allowed to thaw for 36 h at 2°C and then were cooked on an electric conveyor grill (model TBG-60, Magikitch’n Inc., Quakertown, PA) to a target internal temperature of 70°C. Steaks were cooked for a constant time of 6 min, 5 s at a setting of 176°C for the top and bottom heating platens, with the platen height set at 1.85 cm. Peak internal temperature was recorded for each steak using a Type K thermocouple (model 34040, Atkins Technical Inc., Gainesville, FL). After cooking, steaks were allowed to equilibrate to room temperature (20 to 22°C), and up to 10 cores (1.27-cm diam.) were removed parallel to the muscle fiber orientation. Each core was sheared once perpendicular to the muscle fiber orientation using an Instron load frame (model 4443, Instron Corp., Canton, MA) equipped with a Warner-Bratzler shear head (cross-head speed = 200 mm/min). Peak shear force values for individual cores were used to compute a mean peak shear force value for each LM steak.

Statistical Analysis
Individual animal served as the experimental unit for all statistical analyses. Data for carcass traits were analyzed using least squares mixed model procedures of SAS (SAS Inst. Inc., Cary, NC). The statistical model used for carcass traits included the random effect of block, the fixed effect of implant treatment, and individual on-test BW partitioned as a covariate.

Data for WBSF values were analyzed as repeated measures, using least squares mixed model procedures of SAS. The statistical model included the fixed effects of implant treatment, aging period, and the implant treatment x aging period interaction and random effects of block and individual animal within implant treatment, along with cooked steak peak temperature partitioned as a covariate. The repeated statement of the model designated aging period as the repeated variable; options specified for subject and type (covariance structure) were individual animal and spatial power, respectively.

The study was designed to include several a priori comparisons, constructed specifically to examine the effects associated with the number of implants administered during finishing and specific dosage rates of E2 plus TBA. Statistical analyses partitioned treatment effects into the following nonorthogonal contrasts: contrast 1, no implants vs. a single finishing implant (treatment 1 vs. treatments 2, 3, 4, and 5); contrast 2, a single finishing implant vs. 2 sequential finishing implants (treatments 2, 3, 4, and 5 vs. treatments 6, 7, 9, and 12); contrast 3, a low-dose (8 E2:80 TBA) combination implant vs. a moderate-dose (14 E2:140 TBA) combination implant as the initial implant in a 2-implant program (treatments 8 and 10 vs. treatments 9 and 11); contrast 4, a moderate-dose (14 E2:140 TBA) combination implant vs. a high-dose (20 E2:200 TBA) combination implant as the terminal implant in a 2-implant program (treatments 8 and 9 vs. treatments 10 and 11); and contrast 5, the use of TBA alone vs. the use of E2 + TBA (treatments 2 and 6 vs. treatments 5 and 12). In contrast 5, the cumulative dosage of TBA was held constant so that the effect tested was cumulative dosage of E2 (i.e., average effect of 20 vs. 40 mg of E2).

The nonlinear models procedure of SAS was used to fit the following exponential decay model to least squares means for WBSF corresponding to the treatment x aging interaction: WBSF = b2 + b1 expt(–b0t), where b2 = the distance from zero to the asymptote; b1 = the distance from the asymptote to the y-intercept; b0 = a constant rate of change; and t = the time (in d) postmortem (Gruber et al., 2006Go). Instantaneous rates of change at a given time during postmortem storage were estimated by the first derivative of each model: Formula. Coefficients of determination were calculated as the ratio of the residual sums of squares to the corrected total sums of squares.

Frequency distributions of USDA quality grades and frequencies of lean quality defects were analyzed using the GLIMMIX procedure of SAS for generalized linear mixed models. The statistical model used for these analyses included the fixed effect of treatment and block as a random effect. All comparisons were tested using a comparison-wise significance level of {alpha} = 0.05.


   RESULTS AND DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
LITERATURE CITED
 
Implant Treatment Effects on Carcass Characteristics and LM Tenderness
Results characterizing differences in carcass traits and strip loin tenderness among the 12 experimental treatment groups are summarized in Tables 2Go through 4GoGo. Nichols et al. (2002)Go stressed the importance of using an appropriate slaughter end point when testing implant treatment effects and advocated comparison of treatment groups at the same compositional end point [e.g., equal percentage of empty body fat (EBF)]. Data presented in Table 2Go show that treatment groups evaluated in this study did not differ in adjusted fat thickness (P = 0.67) or predicted EBF percentage (P = 0.22), indicating that heifers comprising the 12 treatment groups were compared at similar stages of compositional maturity (Table 2Go).


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  		Table 2. Effects of implant treatment1 on carcass yield-grade characteristics and predicted percentage of empty body fat
 

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  		Table 3. Effects of implant treatment1 on carcass maturity, marbling score, and the percentage of carcasses grading US Choice and Prime
 

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  		Table 4. Effect of the implant treatment1 x aging interaction2 on Warner-Bratzler shear force of the LM
 
Anabolic implants, used commercially for growing and finishing cattle, enhance BW gain and increase muscle mass primarily by increasing the rate of protein accretion (Perry et al., 1991Go), with little (Lemieux et al., 1990Go) or no (Loy et al., 1988Go; Hutcheson et al., 1997Go) effect on fat deposition rate. As a result, implanted cattle normally grow faster and attain a given percentage of EBF at heavier BW than do nonimplanted cattle (Hutcheson et al., 1997Go; Guiroy et al., 2002Go). In addition, due to the effects of implants on skeletal muscle protein gain (Hayden et al., 1992Go; Johnson et al., 1996Go), carcasses produced by implanted cattle typically are heavier and have larger LM area measurements compared with carcasses of nonimplanted cattle (Dolezal, 1997Go; Montgomery et al., 2001Go).

All but 3 of the implant treatments evaluated in the current study (treatments 2, 3, and 4) increased (P < 0.05) HCW and LM area (Table 2Go) when compared with the nonimplanted control (treatment 1). Moreover, due primarily to their larger LM areas (Table 2Go), heifers in some of the more aggressive implant treatments (treatments 9, 10, and 11) had lower (i.e., improved) yield grades (P < 0.05) than did nonimplanted heifers. Treatment differences in estimated percentage of KPH observed in the current study, though statistically significant, were small in magnitude and practically unimportant (Table 2Go).

Despite the proven effectiveness of implants for improving growth performance of growing and finishing cattle (Duckett and Andrae, 2001Go), concerns that the use of implants may reduce carcass quality grade and beef tenderness continue to be expressed (Smith et al., 2006Go). Research conducted to examine the effects of implanting on beef quality characteristics has shown that some implant programs can result in advanced skeletal maturity (Reiling and Johnson, 2003Go), reduced marbling scores (Duckett et al., 1997Go), and decreased beef tenderness (Platter et al., 2003bGo).

In the current study, the treatment main effect was not a significant source of variation in skeletal or lean maturity scores (Table 3Go); however, the effect of implant treatment on marbling score approached significance (P = 0.086) and was of sufficient magnitude to influence (P = 0.013) the percentage of carcasses grading Choice and Prime (Table 3Go). The greatest frequencies of carcasses grading Choice and Prime generally were observed among heifers implanted with 1 or 2 androgenic implants (treatments 2 and 6), a single combination implant (treatments 3 and 5), or 2 low-dose combination implants (treatment 7), whereas the lowest frequencies of Choice and Prime carcasses were observed for heifers implanted with the highest cumulative, combined dosages of estrogen plus androgen (treatments 9, 10, 11, and 12). It has been suggested that finishing implanted and nonimplanted cattle to the same percentage of EBF will diminish or alleviate negative effects of implanting on carcass quality grade (Nichols et al., 2002Go). Our results showed that significant among-group differences in quality grade performance persisted, even though heifers in the various treatment groups were slaughtered at similar compositional endpoints.

Previous studies investigating the effects of heifer implant programs on beef tenderness (Crouse et al., 1987Go; Nichols et al., 1996Go; Kerth et al., 2003Go) have produced variable results. Data from the current study showing implant treatment effects on WBSF values of LM steaks aged for 3, 7, 14, 21, or 28 d are presented in Table 4Go. Treatment interacted with the length of the postmortem aging period to affect (P < 0.001) LM WBSF (Table 4Go). After 3 d of aging, several implant treatments (treatments 7 through 12) resulted in greater (P < 0.05) LM WBSF values when compared with the nonimplanted control group (Table 4Go). As the length of the postmortem aging period increased, however, the effects of the various implant treatments on LM WBSF were gradually diminished so that by 28 d postmortem, only the most aggressive implant treatment (treatment 12) had a greater mean LM WBSF than the control group (Table 4Go). These findings suggest that postmortem aging may be effective for mitigating detrimental effects on tenderness of most mild to moderately aggressive heifer-implant programs.

Effects of Number and Potency of Heifer Finishing Implants
Morgan (1997)Go, after an extensive literature review, suggested that both number and potency of implants administered during finishing influence beef carcass quality characteristics and meat tenderness and concluded that implant programs for feedlot cattle involving the use of high-potency implants, administered more than once, produce the most pronounced, adverse effects on beef quality. Results of a priori contrasts comparing effects of number and potency of heifer finishing implants on carcass yield-grade traits, quality grade characteristics, and LM WBSF are summarized in Tables 2Go, 3Go, and 4Go, respectively.

Control vs. Single Implant.
Compared with the non-implanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg (Figure 1Go) without affecting mean marbling score (Table 3Go), the percentage of carcasses grading Choice and Prime (Figure 1Go), or LM WBSF values (Figure 2Go). Heifers receiving a single implant during finishing produced carcasses that tended to have slightly more advanced (P = 0.052) skeletal maturity compared with carcasses of nonimplanted heifers (nonimplanted = A60; single implant = A66); however, all other carcass traits were similar for the 2 groups (Tables 2Go and 3Go).


Figure 1
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  		Figure 1. Comparison of HCW and the percentage of carcasses grading Choice and Prime for heifers receiving 0 (nonimplanted control), 1 (treatments 2, 3, 4, and 5), or 2 (treatments 6, 7, 9, and 12) implants.

 

Figure 2
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  		Figure 2. Warner-Bratzler shear force (WBSF) of LM steaks. Postmortem aging from a) heifers receiving 0 (non-implanted control), 1 (treatments 2, 3, 4, and 5), or 2 (treatments 6, 7, 9, and 12) implants and b) heifers that received implants containing trenbolone acetate (TBA) or estradiol 17-ß (E2) + TBA.

 
Several previous comparisons of implanted vs. non-implanted heifers have shown that the use of a single finishing implant improves growth performance (ADG and feed efficiency) and increases HCW (Herschler et al., 1995Go; Nichols et al., 1996Go; Duckett et al., 1997Go). Moreover, Duckett et al. (1997)Go reviewed a number of different studies and reported that marbling score, yield grade, quality grade, dark cutter incidence, and WBSF were not affected by implanting heifers once at the beginning of the finishing period. However, Herschler et al. (1995)Go examined the effects of several finishing implants containing the combination of estradiol benzoate (EB) and TBA, delivered at various dosage rates and EB:TBA ratios, and found that heifers receiving a single combination implant at the beginning of the finishing period produced carcasses with lower marbling scores than did nonimplanted heifers. In addition, Nichols et al. (1996)Go reported that, among heifers fed MGA, those implanted with a single implant containing 14 mg of E2 and 140 mg of TBA had greater 14-d LM WBSF values than did nonimplanted heifers. Results of our study suggest that the use of several different TBA-containing implants, administered once at the beginning of a 140-d finishing period to heifers supplemented with MGA, effectively increased HCW, with negligible effects on carcass quality and LM tenderness.

Single Implant vs. Reimplant.
Sequential implanting produces additive effects on weight gain so that additional performance advantages typically are realized with each successive implant (Duckett and Andrae, 2001Go). However, repetitive use of implants often reduces marbling (Morgan, 1997Go) and has been shown to increase the rate of skeletal maturation (Platter et al., 2003bGo; Scheffler et al., 2003Go). Additionally, some studies have shown that sequential implanting can negatively affect beef tenderness (Platter et al., 2003bGo; Scheffler et al., 2003Go).

Results of previous studies involving direct comparisons of the effects of 1 vs. 2 finishing implants on heifer carcass characteristics suggest that reimplanting does the following: a) increases HCW (Berger and Galyean, 2000Go); b) decreases fat thickness, increases LM area, and improves yield grade (Brandt et al., 2000Go; Swingle et al., 2000Go); and c) reduces mean marbling score and decreases the percentage of carcasses grading Choice and Prime (Berger and Galyean, 2000Go; Brandt et al., 2000Go). Kerth et al. (2003)Go found no difference in LM WBSF between heifers implanted either once or twice during finishing. In the current study, the use of 2 sequential finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg (Table 2Go, Figure 1Go) compared with the use of a single implant. Moreover, reimplanting increased (P < 0.001) LM area (single implant = 89.7 cm2; reimplant = 94.5 cm2), reduced (P = 0.024) the percentage of KPH (single implant = 2.0%; reimplant = 1.9%), and improved (P = 0.004) mean yield grade (single implant = 3.37; reimplant = 3.10). However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime (Figure 1Go) and strip loin steaks with greater WBSF values at all postmortem aging times (Figure 2Go) compared with heifers that were implanted once. A noteworthy observation among heifers implanted twice with combination implants was the relationship between 14-d LM WBSF and cumulative, combined dosage of E2 plus TBA (Figure 3Go). Commercially available heifer finishing implants that contain both E2 and TBA are formulated to deliver a 1:10 ratio of E2 to TBA. Data presented in Figure 3Go show that mean 14-d LM WBSF for reimplanted heifers increased linearly as the cumulative, combined dosage of E2 plus TBA increased. These data imply existence of a direct relationship between potency of combination finishing implants and beef tenderness in reimplanted heifers.


Figure 3
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  		Figure 3. Relationship between cumulative combined dosage of estradiol 17-ß (E2) plus trenbolone acetate (TBA) and mean 14-d LM Warner-Bratzler shear force (WBSF) among heifers that received 2 sequential implants.

 
Swingle et al. (2000)Go reported that heifers implanted once during finishing produced significantly fewer dark cutting carcasses than did reimplanted heifers. We also observed (data not shown) that heifers implanted once produced fewer (P = 0.038) dark cutting carcasses (incidence = 0.6%) than heifers implanted twice (incidence = 4.2%). Twelve of the 500 heifers involved in the current study produced carcasses classified as dark cutters, resulting in an overall dark cutter incidence rate of 2.4%; reimplanted heifers produced 11 of the 12 dark cutting carcasses observed in the study. Although noteworthy, these findings should be interpreted cautiously; an adequate test of implant treatment effects on the frequency of dark cutters would require a much larger experimental sample.

Low-Dose vs. Moderate-Dose Initial Implant.
Differences in potency of implants administered early in the finishing period have been shown to influence carcass quality grades. Pritchard (2000)Go reported that non-implanted steers and steers implanted with low-potency implants, early in the finishing period, produced carcasses with similar marbling scores, whereas marbling was reduced by early administration of higher-potency implants.

Results comparing carcass characteristics of heifers that received either a low-dose (8 mg of E2 and 80 mg of TBA) or moderate-dose (14 mg of E2 and 140 mg of TBA) combination implant as the initial implant in a 2-implant sequence are summarized in Tables 2Go and 3Go. Brandt et al. (2000)Go and Hutcheson et al. (2002)Go conducted similar comparisons of low-dose (8 mg of E2 and 80 mg of TBA) and moderate-dose (14 mg of E2 and 140 mg of TBA) initial implants. In their studies, potency of the initial implant had no effect on ADG, feed efficiency, or HCW; however, heifers that received the low-dose initial implant produced a greater percentage of carcasses grading Choice and Prime than did heifers receiving the moderate-dose initial implant (Brandt et al., 2000Go; Hutcheson et al., 2002Go). In the current study, heifers implanted with a low-dose initial implant produced carcasses with slightly more youthful lean maturity scores (P = 0.029); however, none of the other carcass characteristics differed between the 2 groups (Tables 2Go and 3Go).

Kerth et al. (2003)Go compared LM steaks produced by heifers administered low-dose (8 mg of E2 and 80 mg of TBA) vs. moderate-dose (14 mg of E2 and 140 mg of TBA) initial implants and found no difference in 14-d WBSF between the 2 groups. In the current study, heifers receiving a low-dose initial implant tended to have slightly lower (P = 0.09) 7-d LM WBSF values compared with heifers that received a moderate-dose initial implant; however, WBSF values for the 2 groups did not differ at any of the other postmortem aging times (Table 4Go).

Moderate-Dose vs. High-Dose Terminal Implant.
Contrasts comparing carcass characteristics and LM WBSF measurements for heifers that received common initial implants and were reimplanted with either a moderate-dose (14 mg of E2 and 140 mg of TBA) or high-dose (20 mg of E2 and 200 mg of TBA) terminal implant are shown in Tables 2Go through 4GoGo. Hutcheson et al. (2002)Go compared growth and carcass traits of heifers implanted with the same moderate-dose and high-dose terminal implants that were evaluated in the current experiment. In their study, terminal implant dose had no effect on animal performance or HCW. However, heifers implanted with a high-dose terminal implant produced carcasses with larger LM areas, improved yield grades, and lower mean marbling scores compared with carcasses of heifers that received a moderate-dose terminal implant (Hutcheson et al., 2002Go). In our study, neither carcass traits nor LM WBSF values were influenced by terminal implant dose (Tables 2Go through 4GoGo).

Effects of TBA Alone vs. E2 Plus TBA.
Implants that contain TBA as a single, active ingredient have been shown to be effective for enhancing growth performance of finishing heifers (Trenkle, 1992Go; Mader and Lechtenburg, 2000Go) while having minimal effects on carcass or meat quality characteristics (Duckett et al., 1997Go; Kreikemeier and Mader, 2004Go). The response of heifers to TBA is additive to the growth responses elicited by administering exogenous estrogen, by feeding MGA (Hutcheson et al., 1993Go), or both. Therefore, TBA and E2 often are administered together, producing a growth response that exceeds responses achieved with either hormone used alone (Bartle et al., 1989Go). The combined use of E2 and TBA, however, has been implicated as a possible cause of reduced quality grade performance (Belk, 1992Go) and decreased beef tenderness (Roeber et al., 2000Go).

Contrasts comparing carcass traits and LM tenderness of heifers administered implants containing TBA alone vs. those implanted with E2 plus TBA are shown in Tables 2Go through 4GoGo. These contrasts were constructed so that the groups differed only with respect to the inclusion of E2; dosage of TBA was the same for both groups.

Heifers administered implants containing a combination of E2 plus TBA had larger (P = 0.046) LM areas (Table 2Go) and lower (P = 0.004) mean marbling scores (Table 3Go) than did heifers implanted with TBA alone. In addition, heifers implanted with combination implants produced a lower (P = 0.005) percentage of carcasses with marbling scores of Modest or greater (Table 3Go) than did heifers implanted with TBA alone (29.3% for TBA alone vs. 14.6% for TBA plus E2). All other carcass traits were similar for the 2 groups (Tables 2Go and 3Go). Heifers that received implants containing a combination of E2 plus TBA produced steaks that had greater WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging compared with steaks from heifers receiving TBA alone (Table 4Go, Figure 2Go). However, mean WBSF values for the 2 groups did not differ (P = 0.247) when steaks were aged for 28 d (Table 4Go, Figure 2Go).

Our findings suggested that single-ingredient implants containing 200 mg of TBA had no negative effects on carcass quality or meat tenderness, whereas the use of implants containing the combination of 20 mg of E2 and 200 mg of TBA reduced marbling score and increased LM WBSF. From these results, it could not be determined whether observed reductions in marbling and tenderness stemmed from the effects of E2 or from the synergistic effects of E2 plus TBA. Herschler et al. (1995)Go compared carcass traits of heifers implanted with EB alone, TBA alone, or EB plus TBA. All 3 implant treatments reduced mean marbling scores when compared with a nonimplanted control group; however, the reduction in marbling tended to be greatest for heifers implanted with the combination of EB plus TBA.

Postmortem Aging and Predicted Consumer Acceptance of LM Steaks
Managing the length of the postmortem aging period is a critical step in the process of providing consumers with tender beef products (Tatum et al., 1999Go; Gruber et al., 2006Go). Results summarized in Table 4Go suggest that LM steaks from heifers produced using different implant programs would require different postmortem aging periods to attain an acceptable level of tenderness. Correspondingly, an additional analysis was conducted to gain insight into the relationship between postmortem aging and predicted consumer acceptance for LM steaks produced by heifers in the 12 treatment groups.

A logistic regression equation developed by Platter et al. (2003a)Go, which uses LM WBSF to estimate the probability that a LM steak would provide a satisfactory eating experience to a majority (≥2/3) of beef consumers, was used to calculate predicted probabilities of consumer acceptance for LM steaks produced by heifers in each treatment group after 3, 7, 14, 21, and 28 d of aging (Table 5Go). In this analysis (Table 5Go), a predicted probability that exceeds 0.50 denotes greater-than-even odds that the majority of consumers would rate the steak as acceptable in overall eating quality. The greater the probability, the more favorable are the odds of the product delivering a pleasurable eating experience. Values in Table 5Go that are less than 0.50 indicate likelihood of an unsatisfactory eating experience for the majority of consumers.


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  		Table 5. Predicted probability of consumer acceptance1 for LM steaks from heifers in each implant treatment2 after aging for 3, 7, 14, 21, or 28 d
 
Postmortem aging substantially improved predicted consumer acceptability of steaks from heifers in all treatment groups (Table 5Go). Steaks produced by heifers in treatments 1 through 6 required a minimum of 7 d of aging to attain satisfactory levels of eating quality (i.e., predicted probability > 0.50), whereas steaks from heifers in treatments 7 through 12 required at least 14 d of aging to attain satisfactory levels of predicted consumer acceptance. Postmortem aging periods longer than 14 d were effective for reducing among-group differences in predicted consumer acceptance (Table 5Go) and seemed to mitigate detrimental effects of most treatments on predicted acceptability. Steaks from heifers in some treatment groups (treatments 1, 2, 3, 6, and 12) showed little additional improvement in consumer acceptance beyond 21 d of aging; however, consumer acceptance for steaks produced by heifers in several other groups (treatments 4, 5, 7, 8, 9, 10, and 11) continued to improve until 28 d postmortem (Table 5Go). After 28 d of aging, all treatment groups had predicted probabilities of consumer acceptance that ranged from 0.69 to 0.80.

Results summarized in Table 5Go reaffirm the importance of postmortem aging for assuring tenderness and consumer acceptability of strip loin steaks from both nonimplanted and implanted heifers. Strip loins from nonimplanted heifers, heifers implanted once during finishing, and heifers implanted twice with single-ingredient implants containing 200 mg of TBA required a minimum of 7 d of aging but were most likely to provide a satisfactory eating experience when aged 14 to 28 d. Heifers implanted twice with combination implants containing both E2 and TBA produced strip loins that required at least 14 d of aging but were most likely to provide a pleasurable eating experience when aged 21 to 28 d.


   Footnotes
 
1 This project was funded by beef and veal producers and importers through their $1-per-head checkoff and was produced for the Cattlemen’s Beef Board and state beef councils by the National Cattlemen’s Beef Association. We would like to express appreciation to Five Rivers Cattle Feeding for their contributions to this project. Additionally, we would like to express our appreciation to Phillip L. Chapman for assistance with statistical analyses and to Colorado State University graduate and undergraduate students who assisted with this project. Back

2 Corresponding author: J.Daryl.Tatum{at}Colostate.edu.

Received for publication January 2, 2007. Accepted for publication April 2, 2007.


   LITERATURE CITED
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 


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