J. Anim. Sci. 2006. 84:938-945
© 2006 American Society of Animal Science
Residual feed intake of purebred Angus steers: Effects on meat quality and palatability
S. D. Baker*,
J. I. Szasz*,
T. A. Klein*,
P. S. Kuber*,1,
C. W. Hunt*,
J. B. Glaze, Jr.
,
D. Falk*,
R. Richard*,
J. C. Miller*,
R. A. Battaglia* and
R. A. Hill*,2
* Department of Animal and Veterinary Science, University of Idaho, Moscow 83844;
and
Department of Animal Sciences, The Ohio State University, Columbus 43210-1095; and
and
Twin Falls R & E Center, University of Idaho, Twin Falls 83303
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Abstract
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Relationships between residual feed intake (RFI) and other performance variables were determined using 54 purebred Angus steers. Individual feed intake and BW gain were recorded during a 70-d post-weaning period to calculate RFI. After the 70-d post-weaning test, steers were fed a finishing ration to a similar fat thickness (FT), transported to a commercial facility, and slaughtered. A subsample of carcasses (n = 32) was selected to examine the relationships among RFI, meat quality, and palatability. Steers were categorized into high (>0.5 SD above the mean; n = 16), medium (mid; ± 0.5 SD from the mean; n = 21), and low (<0.5 SD below the mean; n = 17) RFI groups. No differences were detected in ADG, initial BW, and d 71 BW among the high, mid, and low RFI steers. Steers from the high RFI group had a greater DMI (P = 0.004) and feed conversion ratio (FCR; DMI:ADG; P = 0.002) compared with the low RFI steers. Residual feed intake was positively correlated with DMI (r = 0.54; P = 0.003) and FCR (r = 0.42; P = 0.002), but not with initial BW, d 71 BW, d 71 ultrasound FT, initial ultrasound LM area, d 71 ultrasound LM area, or ADG. The FCR was positively correlated with initial BW (r = 0.46; P = 0.0005), d 71 BW (r = 0.34; P = 0.01), and DMI (r = 0.40; P = 0.003) and was negatively correlated with ADG (r = –0.65; P = 0.001). There were no differences among RFI groups for HCW, LM area, FT, KPH, USDA yield grade, marbling score, or quality grade. Reflectance color b* scores of steaks from high RFI steers were greater (P = 0.02) than those from low RFI steers. There was no difference between high and low RFI groups for LM calpastatin activity. Warner-Bratzler shear force and sensory panel tenderness and flavor scores of steaks were similar across RFI groups. Steaks from high RFI steers had lower (P = 0.04) off-flavor scores than those from low RFI steers. Cook loss percentages were greater (P = 0.005) for steaks from low RFI steers than for those from mid RFI steers. These data support current views that RFI is independent of ADG, but is correlated with DMI and FCR. Importantly, the data also support the hypothesis that there is no relationship between RFI and beef quality in purebred Angus steers.
Key Words: efficiency • beef • meat quality • palatability • residual feed intake
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INTRODUCTION
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Improving feed efficiency is an important strategy in reducing feed cost and improving profitability. Residual feed intake (RFI), defined as the difference between actual and predicted feed intake required for the observed rate of gain, is one measure of feed efficiency and is moderately heritable and genetically independent of growth rate and BW in growing cattle (Herd and Bishop, 2000
; Arthur et al., 2001a, b). Because RFI is moderately heritable (h2 = 0.16 to 0.43; Herd et al., 2003), it offers a genetic selection method to improve beef cattle efficiency without also increasing growth rate and mature size (Johnston et al., 2002). Selection for efficiency using the RFI trait could potentially improve feed efficiency in cattle through reduced feed intake (Herd et al., 2003). Selection of parents with low RFI (considered efficient) resulted in progeny that consumed less feed as yearlings but weighed the same at slaughter as offspring from high RFI parents (Richardson et al., 2001). In addition, preliminary evidence suggests that selection for RFI probably does not negatively affect mature cow weight or carcass quality of progeny, but can offer an advantage in selection for reduced cow maintenance requirements (Johnston et al., 2002).
Current genetic selection programs are focused primarily on growth and carcass traits, which are easily and inexpensively measured. However, it is important that any process of selection for efficiency does not adversely impact improvements made in end-product quality (Archer et al., 1999). Nevertheless, genetic correlations between RFI and carcass traits in U.S. cattle have not been reported. Therefore, determining the relationships between RFI and meat quality and palatability before genetic selection for improved RFI is worthy of study. An initial step in this process is to investigate these relationships at the phenotypic level. Therefore, the objective of the current study was to determine whether RFI impacts meat quality and palatability characteristics in purebred Angus steers.
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MATERIALS AND METHODS
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Animals, Feeding, and Ultrasound Measures
All procedures involving the use of animals in this study were approved by the University of Idaho Animal Care and Use Committee. Purebred Angus steers (n = 54) that were obtained from a single seedstock producer were transported to the University of Idaho Experiment Station. After being received, the steers were weighed on 2 consecutive days before the morning feeding. After the initial BW measurements and for the subsequent 70 d, steers were fed a growing ration (Table 1) individually using electronic gates (American Calan Inc., Northwood, NH). Steers were provided with fresh feed twice daily, and orts were removed and recorded daily.
During the 70-d test period, steers were weighed every 2 wk. After the 70-d test period, the growing ration was modified in 4 stages to the finishing ration (Table 1
), and steers were fed the finishing ration until their rib fat depth reached approximately 1.2 cm. Ultrasound measures for fat thickness (UFT) and LM area (ULMA) were taken on d –28, 71, and 161 (slaughter group 1) or on d 178 (slaughter group 2) using a Falco 100 real-time ultrasound unit (Pie Medical Equipment Co., Maastrict, The Netherlands) equipped with an 18-cm, 3.5-MHz linear array transducer. Hair was removed, and vegetable oil was applied between the 12th and 13th ribs in preparation for measurements of UFT and ULMA.
Carcass Data Collection and Objective Meat Quality Determination
Steers were slaughtered in 2 groups [based on estimated fat thickness (FT)] on d 165 and 179 at Tyson Fresh Meats (Pasco, WA). A randomly selected subsample (n = 32) of carcasses was chosen for meat quality and palatability analyses. Hot carcass weight was determined immediately after slaughter before chilling at 2°C. After a 24-h postmortem (PM) period, the carcasses (n = 32) were ribbed and allowed to bloom for 45 min. Longissimus dorsi muscle area, FT, KPH, marbling, and maturity were measured by a trained evaluator. Quality grade (QG) and yield grade (YG) were determined according to USDA (1997).
Immediately after ribbing, a 10-g muscle sample (24 h PM) was obtained from the exposed LM at the 12th–13th rib interface from the left side of each carcass, minced, and stored in 25 mL of buffer (50 mM Tris, 10 mM EDTA, 100 mg of ovomucoid/L, 2 mM PMSF, 6 mg of leupeptin/L, and 10 mM ß-mercaptoethanol; pH 8.3). Calpastatin was partially purified by chromatography, and calpastatin activity was determined as described by Shackelford et al. (1994) and modified by Duckett et al. (1998). Samples were assayed to determine calpastatin activity according to Koohmaraie (1990) and Duckett et al. (1998).
Whole boneless strip loins (Institutional Meat Purchase Specification 180; NAMP, 1992) were removed from each carcass by Tyson Fresh Meats personnel and were transported to the University of Idaho Meat Laboratory. Loins were fabricated into 2.54-cm steaks, vacuum-packaged, and aged at 2°C for 1, 3, 7, 14, or 28 d PM. After aging, steaks were stored at –20°C for subsequent analyses.
One steak (1 d PM) from each carcass was trimmed of all external fat, pulverized in liquid nitrogen, and used to determine moisture and ash content (AOAC, 1990). Total lipid of the lean was extracted in chloroform:methanol (Folch, et al., 1957) with slight modifications to determine lipid percentage. Total nitrogen content was determined, and CP was calculated as the percentage of Kjeldahl N x 6.25 (AOAC, 1990). Refractive color was measured from 3 locations on the exposed lean surface of each steak using a Hunter Lab Miniscan colorimeter (Hunter and Associates, Reston, VA) with a port diameter of 31.8 mm and a 180-foot candle light source. Three measurements for color evaluation were made: L* (lightness; range from 0 = black to 100 = white), a* (red-green spectrum; range from –60 = more green, less red to 60 = more red, less green), and b* (yellow-blue spectrum; range from –60 = more blue, less yellow to 60 = more yellow, less blue).
Warner Bratzler shear force (WBSF) was measured on steaks aged for 1, 3, 7, 14, and 28 d. Steaks were broiled on DeLonghi Alfredo grills (model BG-16, De Longhi America Inc., Carlstadt, NJ) to an internal temperature of 71°C (AMSA, 1995) as monitored by copper constantan thermocouples and a Digi-Sense scanning thermocouple thermometer (Cole Parmer, Niles, IL). Steaks were wrapped in plastic film and chilled overnight at 4°C. Six 1.27-cm cores were removed parallel to muscle fiber with a mechanical coring device. Peak shear force values were recorded from cores sheared by a texture analyzer (TA-XT2, Texture Technologies Corp., Scarsdale, NY) equipped with a Warner-Bratzler knife. Crosshead speed was set at 20 cm/min. Peak WBSF values were determined by averaging the values of 6 cores per steak (AMSA, 1995).
Trained Sensory Panel Evaluation of Meat Quality
A 9-person trained sensory panel (Cross et al., 1978; AMSA, 1995) evaluated palatability (tenderness, juiciness, flavor, and off-flavor) differences among steaks. Steaks previously aged for 7 d were thawed overnight at 4°C and broiled on DeLonghi Alfredo grills. After an internal temperature of 71°C was reached (AMSA, 1995), steaks were removed from the grill, and external fat was removed. Steaks were cut into 2.54- x 1.27- x 1.27-cm cubes and served warm to each panelist. Panelists evaluated 8 samples per session (2 sessions daily) for tenderness (1 = extremely tough to 10 = extremely tender), juiciness (1 = dry to 10 = juicy), flavor (1 = bland to 10 = intense), and off-flavor (1 = none detectable to 10 = pronounced) using a 10-point scale with anchored end points (AMSA, 1995).
RFI Computations and Statistical Analysis
Statistical analyses were conducted using the SAS system (Version 8, SAS Inst., Inc., Cary, NC). Residual feed intake was calculated as the difference between actual and predicted feed intake by regressing DMI on mid-test BW0.75 and ADG (Koch et al., 1963). Using stepwise regression techniques in PROC REG, ultrasound measurements (ULMA and UFT) were also included in the model. Residual feed intake was defined as the difference between actual DMI and DMI predicted by the regression model. Overall correlations were calculated among measures of growth efficiency and performance and carcass measures using the CORR procedure of SAS.
After determination of RFI, steers were classified into high (>0.5 SD above the mean; n = 16), medium (mid; ± 0.5 SD from the mean; n = 21), and low (<0.5 SD below the mean; n = 17) RFI groups. A mixed linear model (using the MIXED procedure) was employed to test the effect of RFI grouping on growth performance and carcass measurements. When a significant RFI group effect was noted (P < 0.10), means generated by the LSMEANS statement were partitioned using the PDIFF option of SAS. The MIXED procedure was also used to analyze WBSF measured across aging time.
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RESULTS
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RFI
The final model for predicting DMI was:
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where MBW = mid-test BW0.75. This model resulted in a minor improvement over the conventional model including ADG and mid-test BW0.75 alone (R2 = 0.71 vs. 0.68, respectively). Mean performance variables for steers were DMI, 9.8 kg/d; ADG, 1.4 kg/d, feed conversion ratio (FCR), 7.1; initial BW, 341 kg; and d 71 BW, 438 kg (Table 2). Residual feed intake was positively correlated with DMI (r = 0.54; P = 0.003) and FCR (r = 0.42; P = 0.002) but was not correlated (r < 0.10) with BW measurements or ADG (Table 3). Feed conversion ratio was positively correlated with initial (r = 0.46; P = 0.0005) and d 71 BW (r = 0.34; P = 0.01) and DMI (r = 0.40; P = 0.003), but was negatively correlated with ADG (r = –0.65; P = 0.001). Although ADG and BW measurements were similar among RFI groups, the high RFI steers had greater DMI (P = 0.004) and FCR (P = 0.002) than did the low RFI steers (Table 4). No differences were noted between mid RFI steers and low or high RFI steers for any of the performance variables measured.
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Table 2. Mean, SD, and range of performance traits of purebred Angus steers measured for residual feed intake (RFI)
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Table 3. Partial correlations (P-values) of residual feed intake (RFI) and feed conversion ratio (FCR; DMI:ADG) with other performance traits and ultrasound carcass measures in purebred Angus steers
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Table 4. Performance traits of purebred Angus steers classified into high (>0.5 SD above the mean; n = 16), medium (mid; ± 0.5 SD from the mean; n = 21), and low (<0.5 SD below the mean; n = 17) residual feed intake (RFI) groups (n = 54)
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Relationships Between RFI and Ultrasound Measurements
Mean performance data for ultrasound measures determined on d –28 (initial) and 71 are shown in Table 2. Overall, initial UFT was 0.32 cm, and at d 71, UFT was 0.67 cm. Initial ULMA was 40.8 cm2, and at d 71, ULMA was 57.1 cm2. Initial ULMA was positively correlated with FCR (r = 0.64; P = 0.001) but was not correlated with RFI (Table 3). Initial UFT, d 71 UFT, and d 71 ULMA were not related to FCR or RFI. No differences were noted between high, mid, or low RFI steers for initial UFT, d 71 UFT, initial ULMA, and d 71 ULMA (Table 4).
Carcass Traits and Objective Meat Quality Parameters
Differences between RFI groups were not detected for HCW, LM area, FT, KPH, YG, marbling score, or QG (Table 5). There were no differences in L* or a* values across RFI groups. Steaks from high RFI steers had greater (P = 0.02) b* values compared with those from low and mid RFI steers. Cooking loss from steaks was lower (P = 0.005) for mid vs. low RFI steers. Calpastatin activity was similar for high and low RFI groups. Shear force did not change significantly and tended to decrease over PM aging time in all of the RFI groups (RFI group by time, P = 0.09; Figure 1). Shear force values were negatively correlated (r = –0.47; P < 0.0001) with PM aging period (data not shown).
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Table 5. Carcass characteristics of purebred Angus steers classified into high (>0.5 SD above the mean; n = 16), medium (mid; ± 0.5 SD from the mean; n = 21), and low (<0.5 SD below the mean; n = 17) residual feed intake (RFI) groups (n = 32)
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Figure 1. Effect of postmortem aging time on Warner-Bratzler shear force (WBSF) of LM steaks from high (inefficient), medium (mid), and low (efficient) residual feed intake (RFI) purebred Angus steers.
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Sensory Taste Panel
Ratings of tenderness and flavor were not different among steaks from steers across RFI groups (Figure 2).
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Figure 2. Impact of residual feed intake (RFI) grouping on sensory panel palatability ratings of LM steaks. Tenderness was rated from 1 = extremely tough to 10 = extremely tender; juiciness was rated from 1 = extremely dry to 10 = extremely juicy; flavor was rated from 1 = bland to 10 = intense beef flavor; and off-flavor was rated from 1 = none detectable to 10 = pronounced. a,bBars within a palatability variable with different letters tend to differ (P < 0.1).
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DISCUSSION
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Previous reports indicate that phenotypic correlations between RFI and ADG and body size are close to zero (Koch et al., 1963; Jenson et al., 1992; Arthur et al., 1997; Archer et al., 1998; Arthur et al., 2001a, b; Basarab et al., 2003; Crews et al., 2003). Data reported in the current study are consistent with these reports, indicating that RFI is independent of ADG in growing purebred Angus steers.
Herd and Bishop (2000), Herd et al. (2003), and Arthur et al. (2001a, b) reported moderately positive phenotypic correlations between RFI and DMI of Hereford, Angus, and Charolais cattle. In agreement, Basarab et al. (2003) reported a similar positive correlation (r = 0.42) for steers from 5 genetic backgrounds. The current study also found a positive correlation (r = 0.59) between RFI and DMI measured on Angus steers.
Previous reports (Herd and Bishop, 2000; Arthur et al., 2001a; Basarab et al., 2003) have also reported positive correlations between FCR and RFI (r = 0.53, 0.70, and 0.44, respectively). The results from the current study were also consistent with the previous studies, as a small, positive correlation (r = 0.37) between FCR and RFI was observed. Feed intake and FCR were both greater (less efficient) in high RFI steers than in low RFI steers. These data are consistent with findings from Basarab et al. (2003), who reported that low RFI steers consumed 10.4% less DM and had a 9.4% improvement in FCR over high RFI steers. These data suggest that low (more efficient) RFI steers consume less feed, thus decreasing the amount of feed per kilogram of gain and thereby improving FCR and increasing feed efficiency.
Increasing feed efficiency can have a major influence on the overall profitability of beef cattle production systems. Basarab (1999) reported that cost of feed is second only to fixed costs in importance to the profitability of commercial beef operations. Because RFI appears to be independent of other known performance traits, a savings in feed and energy costs used to produce feed (including fossil fuel savings) may be expected. Published data (Archer et al., 2004) using 2 different models estimate that long-term improvement in profitability may be between 9 and 33%.
Performance traits and their correlations with RFI and FCR are well documented in the literature; however, the biological drivers of variation in RFI are largely unknown. Herd et al. (2004) suggested that there are likely at least 5 major processes by which variation in efficiency can arise: intake of feed, digestion of feed, metabolism, activity, and thermoregulation. Furthermore, modulation of energy use via physiological processes appears to have the potential to account for a substantial proportion of individual variation in efficiency (Hill and Herd, 2001). Given the present lack of understanding of the biological basis of RFI and its effect on various traits, any selection for RFI in beef cattle systems should be accompanied by monitoring for correlated responses; clearly, more research is needed to fully understand the possible effects of RFI on end-product quality.
It appears that the relationships among RFI, FT, and intramuscular fat may not be the same in purebred or crossbred groups of cattle, as there are some inconsistencies in the data reported to date. In the current study, no differences (P > 0.05) existed in HCW, LM area, FT, KPH, YG, marbling score, or QG among the 3 RFI groups. There is evidence of a genetic relationship between RFI and subcutaneous FT, suggesting that low RFI cattle may be leaner. Herd and Bishop (2000) reported negative phenotypic (r = –0.22) and genetic (r = –0.43) correlations between RFI and estimated lean content in Hereford cattle. Reports on the relationship between RFI and intramuscular fat are not conclusive. Robinson et al. (1999) reported a small, positive genetic correlation (r = 0.17) between RFI and intramuscular fat. In agreement with the current study, McDonagh et al. (2001) found no differences in visual marbling scores or objectively measured intramuscular fat for carcasses of a group of Angus, Angus x Hereford, Angus x Polled Hereford, and Angus x Shorthorn steers, which were the progeny of high or low RFI selection lines. However, Richardson et al. (2001) reported progeny from Angus cattle selected for low RFI had 13.2% less subcutaneous and intramuscular fat than progeny from those selected for high RFI. The difference between these studies may be due to differences in age and maturity of animals when traits were measured or may suggest that other unidentified variables may be influencing composition in these populations.
Literature reports of correlations between RFI and ultrasound measurements of subcutaneous fat, intramuscular fat, rump fat, and carcass fat measurements are also inconclusive. Arthur et al. (2001a) reported low phenotypic (r = 0.14) and genotypic (r = 0.l7) correlations between RFI and UFT and ULMA. Basarab et al. (2003) reported a tendency (P = 0.11) for ultrasound marbling to be correlated with RFI (r = 0.13) but found no relationship between RFI and marbling score. In a preliminary study, Crews et al. (2003) reported negative correlations between RFI and FT and between RFI and marbling scores. Jenson et al. (1992) also reported negative correlations between RFI and carcass fat percentage. Carstens et al. (2002) found that high RFI cattle had greater rump FT, but similar FT and intramuscular fat compared with low RFI steers.
Increases in IMF can result in more desirable QG in beef cattle, improving beef palatability and increasing market value of carcasses. Although previous reports have been inconsistent, the current study suggests variation in RFI does not correlate with visual marbling scores and intramuscular fat in Angus steers. It may be that less efficient steers (high RFI) have a greater propensity to deposit fat than protein. Studies that have reported decreased subcutaneous FT in low (more efficient) RFI steers also report that this is not accompanied by a reduction in HCW or LM area. This suggests that YG are not compromised, and low RFI steers may actually have increased retail meat yield. However, other researchers suggest ongoing selection for low RFI may decrease subcutaneous fat levels, possibly leading to animals that fail to meet minimum market specifications for fatness (McDonagh et al., 2001). Data from the current study do not support this notion, as carcasses from all groups had acceptable QG and YG.
Steaks from mid RFI steers tended to have greater protein level percentages than steaks from low RFI steers, lower lipid level percentages than steaks from high RFI steers, and greater moisture level percentages than steaks from high RFI steers. These data may indicate that steaks containing the greatest amount of protein also had the greatest amount of moisture, which is consistent with documented muscle biology. Faustman et al. (1998) suggested that moisture retention can impact palatability of a cooked product and may also influence product weight and, thus, economic return. In the current study, a negative correlation between lipid percentage and protein percentage was observed, which is consistent with reports that steaks having greater moisture and protein content will have decreased lipid content (Garrett and Hinman, 1971; Brackebusch et al., 1991).
Reflectance color values of steaks from high RFI steers showed a tendency to be lighter than steaks from low RFI steers and were more yellow than steaks from both mid and low RFI steers. McDonagh et al. (2001) reported no color differences between steaks from high and low RFI steers. In that study, a trained assessor from Australia scored longissimus dorsi muscle color by comparison against industry-standard colored strips, where 1 = light pinkish-red to 9 = dark red. That is a substantially different and simpler system from that used in the United States, including the current study. Although the data from the current study may suggest color differences of steaks between RFI groups, the data were tightly grouped about the means, and the differences were numerically small. Thus, these small differences in color values may have little practical impact, although there may be an underlying biological basis for these differences that we presently do not understand. Although steaks from low RFI steers appeared to have the greatest off-flavor scores, the maximum value detected was 1.2 (on a 10-point scale), indicating that off-flavor scores were not in an objectionable range and, thus, not detrimental to the eating quality of steaks from low RFI steers.
Numerous studies indicate that increased levels of calpastatin appear to be highly related to decreased tenderness in beef LM (Shackelford et al., 1991b; Morgan et al., 1993; Wulf et al., 1996). However, greater levels of calpastatin in muscle in living animals may be beneficial in that increased calpastatin may decrease protein breakdown and help contribute to the efficiency of energy use in muscle (McDonagh et al., 2001). There is conflicting evidence as to whether there is a relationship between RFI and calpastatin activity in beef LM. We were unable to detect differences in calpastatin activity between high and low RFI steers; however, McDonagh et al. (2001) reported 13% greater calpastatin activity in muscle tissue from low RFI steers compared with high RFI steers, suggesting that more efficient steers may have decreased meat tenderness in comparison with less efficient steers. McDonagh et al. (2001) measured calpastatin activity on samples immediately after slaughter, whereas calpastatin activity levels in the current study were measured 24 h PM. Koohmaraie (1992) found that free calcium levels increased from 1 µM to approximately 100 µM during the first 12 h PM, activating µ-calpain and calpastatin. Substantial reduction in the activity of the calpain system in bovine LM is the most rapid during the first 24 h of aging, and the decline in µ-calpain is more rapid than that in calpastatin (Koohmaraie et al., 1987). Numerous studies (Whipple et al., 1990; Shackelford et al., 1991a, b) report that enzyme activity is not stable immediately after slaughter; thus, researchers recommend the optimal time to measure calpastatin activity is 24 h PM. Therefore, the data of McDonagh et al. (2001) may be less reliable in indicating calpastatin activity than the current study.
There was no difference in WBSF values among high, mid, and low RFI groups for any aging period. All steaks over the aging periods tested from high and low RFI groups sheared 
3.7 kg, falling within the industry standard range (<4.1 kg) for acceptable eating quality (Huffman et al., 1996). In agreement with the current study, McDonagh et al. (2001) reported no differences in shear force values or compression values of LM steaks aged for 1 or 14 d between high and low RFI steers. Further, LM samples aged for 14 d from both high and low RFI steers had shear force values of <4.2 kg, which would be considered acceptable in tenderness by Australian (Shorthose et al., 1998) and American (Huffman et al., 1996) consumers. However, myofibril fragmentation index was lower (less fragmentation) in samples from low RFI steers when compared with samples from high RFI steers for LM steaks aged 1 and 14 d, suggesting that steaks from low RFI steers may be tougher. However, they reported no differences in shear force values.
Using sensory panel evaluation, there were no differences in tenderness or flavor scores among steaks from high, mid, or low RFI steers. Juiciness scores tended to be lower (P = 0.10) in steaks from high RFI steers compared with steaks from mid and low RFI steers. Cook loss percentages were greater (P = 0.005) in steaks from low RFI steers than in steaks from mid RFI steers. These data seem conflicting, as steaks from mid RFI steers had the greatest moisture percentage, but the lowest cooking loss percentages. A possible explanation of this observation may be that steaks from mid RFI steers had proteins that were better able to bind strongly with water, allowing less free water to be lost as drip loss. Proteins are able to bind more strongly when pH is increased, allowing less free water (Ledward et al., 1992). Therefore, steaks with increased ultimate pH values normally exhibit increased moisture retention because naturally occurring water is tightly bound to proteins. Thus, there appears to be no relationship between RFI and eating quality of steaks as assessed by sensory panel evaluation.
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IMPLICATIONS
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These data support the hypothesis that meat quality and palatability are not different between high (inefficient) and low (efficient) residual feed intake Angus steers. The current study detected no adverse relationships between residual feed intake and meat quality or palatability. It appears that residual feed intake has the potential to be included in genetic selection programs in the United States, providing several benefits (including reduced feed costs), without compromising carcass quality or meat palatability. Presently, there is a lack of understanding of the biological basis to variation in residual feed intake and of its genetic association with meat quality traits. Thus, selection for residual feed intake should be accompanied by monitoring for any correlated response in meat quality and palatability.
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Acknowledgements
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The excellent cooperation of the Kast family (King Hill, ID), who provided purebred Angus steers for this study, is gratefully acknowledged.
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Footnotes
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1 Current address: Department of Animal Sciences, The Ohio State University, Columbus 43210-1095. 
2 Corresponding author: rodhill{at}uidaho.edu
Received for publication September 7, 2005.
Accepted for publication November 16, 2005.
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LITERATURE CITED
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Abstract
INTRODUCTION
