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ANIMAL PRODUCTS |
Department of Animal Sciences, Washington State University, Pullman 99164-6351
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Beef • Carcass Characteristics • Color • Growth • Palatability
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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showed that methane emission was minimized, and dietary ME content was maximized, at 6% tallow addition to a barley-based finishing diet fed to wethers. Fiber digestion was also decreased, which might increase its effective fiber content, reducing the need for dietary forage (Nelson et al., 2001).
Beef shelf life stability and palatability may be affected by feeding a high-linoleic acid supplemental fat to steers to increase the amount of conjugated linoleic acid. Considering the potential importance of CLA in human health (see review by McGuire and McGuire, 1999) and the ability of specific ruminal bacteria to convert linoleic acid to CLA (Harfoot and Hazlewood, 1988), feeding supplemental fats that are high in linoleic acid may be a practice that could benefit the beef industry. However, it is also important that we understand the effects fats have on beef quality and palatability due to altered fatty acid content. Yellow restaurant grease (RG) is higher in unsaturated 18C fatty acids (especially linoleic acid) than tallow. Several studies have been conducted to determine whether RG and tallow affect feedlot performance (Zinn, 1988; Plascencia et al., 1999; Plascencia and Zinn, 2001), but to our knowledge, no published studies have evaluated the effects of RG and tallow on the beef quality and palatability attributes. Therefore, the objective of this study was to determine effects of RG or tallow and forage level in barley-based finishing diets on feedlot performance, appearance, shelf life, carcass characteristics, and beef palatability.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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). Animals and Feeding
One hundred sixty-eight crossbred yearling steers (317.1 ± 1.0 kg) were vaccinated with UltraChoice 8 (Pfizer Animal Health, New York, NY) and Bovi-Shield 4 (Pfizer Animal Health), treated for parasites with IVOMEC-plus (MSD-AgVet, Rahway, NJ), injected with 5.5 mg of Se/100 kg of BW (MU-SE; Schering-Plough, Animal Health Corp., Union, NJ), and implanted with Revalor S (Hoechst Roussel Vet, Warren, NJ). Steers were blocked by BW (obtained on two consecutive days after a 12-h fast) into three blocks, and assigned randomly within each block to one of seven pens (eight steers per pen). Each pen was 4.9 x15.2 m, with a roof that covered the feed bunk and 5 m of the pen. Pens, within block, were assigned randomly to dietary treatments in a 3 x2 + 1 factorial arrangement. Main effects were level of yellow RG (0, 3, or 6%) and level of alfalfa hay (AH; 3.5 or 7.0%), with an added treatment of 6% tallow with 7.0% AH (all dietary levels are expressed on a DM basis).
Baronesse barley was steam-rolled with the roller mill set at 1 mm between the rolls and 11,567 kg of pressure. Alfalfa was chopped through a 2.54-cm screen, and potato by-product (PB) consisted of uncooked potato pieces (hopper box) ensiled in a covered bunker silo until fed. Hot RG (Baker Commodities, Spokane, WA) or tallow (Tyson Foods, Inc., Wallula, WA) was sprayed onto the steam-rolled barley in a horizontal mixer in amounts so that 0, 3, or 6% dietary RG or 6% tallow DM was absorbed by the barley.
Steers were adapted over a 20-d period to the final diets containing 0, 3, or 6% RG or 6% tallow plus 15% PB steam-rolled barley, 15% PB, 7% supplement (Table 1), supplemental fat (0, 3, or 6% RG or 6% tallow) and 3.5 or 7.0% AH on a DM basis. Steers were fed (DM basis) diets of 53% grain plus fat, 40% alfalfa, and 10% supplement for 10 d, and then diets of 73% grain plus fat, 20% alfalfa, and 7% supplement for the last 10 d of adaptation. Potato by-product was increased by 7.5 percentage unit increments and supplemental fat was increased in 3 percentage unit increments in each of the two adaptation diets. Diets were formulated to meet, or exceed, the nutrient requirements of steers (NRC, 1996), and contain at least 13.5% CP, 0.52% Ca, 0.26% P, 0.15% S, 0.65% K, 0.10% Mg, 8.8 g of Tylan/t, 33 g of Rumensin/t, and 2,200 IU of vitamin A/kg (diets provided 417 IU of vitamin E/steer daily).
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).
Final steer weights for calculation of ADG and G:F were hot carcass weight divided by 63% (standard dressing percent) and accounting for an additional loss of 3% live weight in transit. The NEm and NEg concentrations of the diets were calculated interatively (Zinn and Owens, 1993) using the relationships NEg = (0.877 NEm) – 0.41 (NRC, 1996), energy gain (Mcal/d) = (0.0557 BW0.75) xADG1.097 (NRC, 1996), and maintenance energy (Mcal/d) = 0.077 BW0.75 (Lofgreen and Garrett, 1968).
Feed samples were collected weekly and composited (wt/wt) on a DM basis. Composite samples were ground to pass a 1-mm screen in a Wiley Mill after air-drying. Feed, ort, and fecal samples (except for RG and tallow) were analyzed for DM (oven dried at 50°C), OM (ashed at 600°C for 6 h), CP (macro-Kjeldahl; AOAC, 1990), and NDF (Procedure A), ADF, and ADL according to Van Soest et al. (1991), whereas feed samples were analyzed for starch content following procedure of Åman and Hesselman (1984). Fatty acid contents of feed samples, using toluene extraction and C24:1 as an internal standard, were quantified (Sukhija and Palmquist, 1988) relative to a standard, containing myristic acid (C14:0), myristoleic acid (C14:1Delta;9), pentadecanoic acid (C15:0), pentadecenoic acid (C15:1 Delta;10), palmitic acid (C16:0), palmitoleic acid (C16:1 Delta;9), margaric acid (C17:0), 10-heptadecenoic acid (C17:1 Delta;10), stearic acid (C18:0), oleic acid (C18:1 Delta;9), linoleic acid (C18:2 Delta;9,12), linolenic acid (C18:3 Delta;9,12,15), arachidic acid (C20:0), and behenic acid (C22:0).
Moisture, insoluble matter, unsaponifiable matter, and fat color were measured on RG and tallow (AOCS, 1990). Whole barley samples, after cleaning, were measured for volume-weight and kernel size distributions. Plump barley kernels were defined as kernels retained on a 0.24 x1.91 cm sieve (Seedburo Equipment Co., Chicago, IL), medium kernels were retained on a 0.20 x1.91 cm sieve, and thin kernels passed through a 0.20 x1.91 cm sieve (USDA, 1975).
Steam-rolled barley samples were separated using tared Tyler standard screen scale sieves (W.S. Tyler Co., Cleveland, OH) with 2,000-, 1,000-, 500- and 250-µm openings and a bottom pan. Samples were drysieved by being placed on the top sieve and shaken in a mechanical horizontal-plane shaker until equilibrium of weight retained was reached (Nelson, 1988). Dry sieving was selected as the method of choice because Van Soest (1994) suggested that dry sieving tended to separate particles by cross-sectional diameter, whereas wet sieving separated particles by length. Therefore, dry sieving was more appropriate for cubical particles. Standard normal deviates (probits) of cumulative fraction of weight undersize (y) or passing through a sieve size (x) were fitted to the equation y = a + b log10x. For each logarithmic normal distribution, log10 mean particle size (log10 µ) and log10 standard deviation (log10 
) were estimated by – a/b and 1/b, respectively (Waldo et al., 1971).
Carcass Data Collection and Muscle Sampling.
The heaviest block was slaughtered after 146 d, and the middle and lightest blocks after 175 d on feed. Steers were shipped 320 km from the feedlot to a commercial plant, where they were humanely slaughtered the day of shipment. Carcasses were weighed, chilled for 24 h at –1 to 0°C, and then carcass measurements, including LM area, 12th-rib fat thickness, percentage of kidney, pelvic, and heart fat, marbling and maturity scores, and quality grades (USDA, 1996), as well as Japanese beef color (1 = very pale to 7 = very dark), brightness (1 = very dull to 5 = very bright), firmness (1 = very soft to 5 = very firm), and texture (1 = very coarse to 5 = very fine), and fat color (1 = very white to 7 = very yellow) and luster (1 = very dull to 5 = very lustrous) scores (JMGA, 1988), were obtained by trained university personnel.
Longissimus Muscle Sampling.
A boneless strip loin roast was removed from the left side of four randomly selected carcasses per pen (84 total). Strip loins were removed beginning at the 13th rib and continuing to a horizontal cut made 15.3 cm posterior to the 13th rib resulting in 1.5- to 2.4-kg strip loin sections that were vacuum-packaged, transported in coolers on ice to the Washington State University Meat Laboratory, and aged at 2°C until 14 d postmortem. After aging, wholesale purge (moisture loss during aging) was measured, all s.c. fat was removed, and, beginning at the anterior end, one 1.3-cm-thick, another 1.3-cm-thick, and three 2.5-cm-thick steaks were sliced. The first steak was used for determination of fatty acid composition (Marks et al., 2004), the three 2.54-cm-steaks were used for Warner-Bratzler shear force (WBSF) determinations, simulated retail display, and trained sensory panel evaluations, respectively, and the second 1.3-cm slice was used for drip loss and pH determination. Steaks for WBSF and trained laboratory sensory panel were vacuum-packaged, immediately frozen, and stored at – 40°C for subsequent evaluation.
Moisture Retention Properties.
To measure purge loss, the strip loin section was removed from the packaging and weights of the strip loin section and vacuum bag (dried at 50°C) were used to calculate purge loss percentage. The lateral half of the 1.3-cm-thick LM steak was weighed, placed in a Whirl Pack (NASCO, Ft. Atkinson, WI) bag, and suspended in a 1°C cooler. After 24 h, the sample was reweighed to determine percent drip loss (Nelson et al., 2000). Thaw drip loss was determined on steaks used for WBSF using similar procedures as that for wholesale purge. The pH was determined at 14 d postmortem using a Fisher Scientific (Pittsburgh, PA) Accumet basic pH meter with a combination electrode after mincing a 5-g (wet weight) sample in 20 mL of distilled water with a Ten Broeck tissue grinder (Pyrex No. 7727–40, Corning, Corning, NY) at 17°C.
Simulated Retail Display.
Steaks for simulated retail display were packaged in retail Styrofoam trays with oxygen-permeable, PVC overwrap, and placed in a cooler at 2 to 3°C. Steaks were stored and scored under 1,075 lx from soft white fluorescent bulbs (General Electric Corp., Cleveland, OH). A trained, four-member panel independently scored each sample on d 0, 1, 3, 5, and 7 after packaging for color (6 = bright cherry red, 5 = cherry red, 4 = red, 3 = slightly brown, 2 = brown, and 1= very brown; AMSA (1995) and purge (1 = no purge, 2 = very small amount of purge, 3 = small amount of purge, 4 = moderate purge, 5 = slightly abundant purge, and 6 = abundant purge). Increments of 0.5 of a score were allowed for both color and purge panel. Panelist scores were averaged for each steer, and then individual steer values were averaged within a pen. A MiniScan XE LAV (Hunter Associates Laboratory, Reston, VA) spectrocolorimeter was used to obtain L* (darkness to lightness), a* (green to red spectrum), and b* (blue to yellow spectrum) values using D65 illuminant and the 10°standard observer settings. Large pieces of connective tissue and fat were avoided, and the six readings per steak were averaged for statistical analysis.
Cooking Attributes, Warner-Bratzler Shear Force, and Trained Sensory Panel.
Shear force analysis was conducted using a modification of AMSA (1995). Steaks were thawed for 30 h at 2°C, broiled on Farberware Open Hearth grills (model R4550; Farberware, Bronx, NY) to an internal temperature of 71°C, as monitored by a Digi-Sense scanning thermocouple thermometer (Model 692–8010; Barnart Co., Barrington, IL), cooled to room temperature, and cooking loss percent was determined. Four 1.27-cm cores from the lateral half of each steak were obtained parallel to the muscle fibers. Cores were sheared once through the center on a TA-XT2 texture analyzer, (Texture Technologies Corp., Scarsdale, NY) equipped with a WBSF attachment using a crosshead speed of 20 cm/min (Wheeler et al., 1997). For statistical analysis, the values of the four cores were averaged.
Steaks for trained panel analysis were thawed and cooked as described for WBSF. After cooking, external fat and major connective tissue were removed. Cooked steaks were cut into 1.0 x1.0 x2.5-cm pieces, and samples were served immediately to an eight-member trained sensory panel (AMSA, 1995). Panelist used a 10-cm unstructured line labeled at each end (Stone and Sidel, 1985) to rate samples on initial and sustained tenderness (0 = tough to 10 = tender), initial and sustained juiciness (0 = dry to 10 = juicy), beef flavor intensity (0 = bland to 10 = intense beef flavor), and off flavor (0 = no off-flavor to 10 = pronounced off-flavor). A ruler was used to determine panelist scores.
Statistical Analyses.
Data, except for simulated retail display, were analyzed as a randomized complete block design with a 3 x2 + 1 factorial arrangement of dietary treatments using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Pen was the experimental unit for all analyses. Main effects were level of RG (0, 3, or 6%) and level of AH (3.5 or 7%), with the added treatment of 6% tallow with 7.0% AH. Least squares means were separated by preplanned contrasts for linear and quadratic effects of RG, AH level, RG xAH, and 6% RG vs. 6% tallow with 7.0% AH (Steel and Torrie, 1980). Simulated retail display data were analyzed as a repeated measures design (Gill and Hafs, 1971), with the whole plot arranged as above and display day in the subplot. Linear, quadratic, and cubic contrasts for display day were calculated. The treatment xblock interaction (12 df) was used to test the whole plot, whereas residual error (56 df) was used to test the subplot.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Volume weights of whole barley and corn averaged 65.0 kg/hL on an air-dry basis, and 60.0 kg/hL on a DM basis. Volume-weights of steam-rolled barley averaged 55.8 kg/hL on an air-dry basis and 49.8 kg/hL on a DM basis. The proportion of plump, normal, and thin barley kernels averaged 83.1, 14.8, and 2.1%, respectively. Black kernels averaged 0.5%, and the barley was U.S. No. 1 (USDA, 1975). Steamrolled barley sieve data seemed to adequately fit the logarithmic normal distribution (Waldo et al., 1971). Mean r2 value was 0.99, skewness value was –0.28, and kurtosis value was – 2.23. Average log10 3 value was 3.61 and log10 value was 0.53 for steamrolled barley. Particle size distribution was similar to Baronesse barley (Nelson et al., 2000) and Camelot barley (Nelson et al., 2001).
The barley (Table 2) had CP, starch, fiber, and ash values similar to those reported by Duncan et al. (1991), by NRC (1984) for Pacific coast barley, and by NRC (1996) for heavy barley grain. The PB (Table 2) contained less CP than NRC (1984), and less CP and fiber but greater starch compared with previous studies from our laboratory (Duncan et al., 1991; Nelson et al., 2000). The AH used in this study was similar in composition to late-bloom alfalfa in NRC (1996).
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and Nelson et al. (2001). Barley fatty acids contained more C16:0 and less C18:2 than those measured by Palmquist (1988) and Miller et al. (1996), but were similar to a previous study by Nelson et al. (2000). The fatty acid content and composition of tallow was similar to those reported by Palmquist (1988), and similar to the tallow and RG reported by Grummer and Klopfenstein (1996).
Alfalfa fatty acids contained more C16:0 and C18:0 and less C18:2 and C18:3 than that reported by Palmquist (1988) and Nelson et al. (2001). The fatty acid content of the control diet was low; thus, fatty acids deposited in muscle tissue would be largely from de novo fatty acid synthesis and smaller amounts from microbial synthesis. Tallow and RG contained 0.22 and 0.23% moisture, 0.03 and 0.18% insoluble matter, 0.42 and 0.32% unsaponifiable matter, and fat advisory committee colors of 1 and 21, respectively.
Diet Digestibilities.
All subclass means are shown in Table 3, but only main effect means are discussed due to no significant (P >0.10) RG xAH interactions. On d 93 and 94, increasing dietary AH increased (P <0.05) DMI (8.7 vs. 9.6 ± 0.35 kg/d). This was probably due to the low DMI of all three pens fed 6% RG and 3.5% AH, which may have been in response to diet energy density. Digestibilities of DM, OM, cell solubles, NDF, ADF, and cellulose were not (P >0.10) affected by diet and averaged 75.4 ± 0.91, 76.7 ±0.88, 80.9 ±0.78, 46.3 ±1.93, 35.9 ±1.5 and 36.8 ±1.29%, respectively. Values were similar to those noted with tallow addition to a barley diet fed to sheep by Nelson et al. (2001); however, increasing dietary RG linearly decreased (P <0.01) hemicellulose digestibility from 65.8 to 50.4 ± 3.72%. Structural carbohydrate fermentation was decreased by more than 50% when fat was added to diets fed to sheep (Ikwuegbu and Sutton, 1982; Nelson et al., 2001) and dairy cattle (Jenkins and Palmquist, 1984). However, evidence exists that fat does not decrease fiber digestion by coating fiber particles (Ørskov et al., 1978; Drackley et al., 1994; Mir, 1998). However, if fat decreases protozoal numbers and bacterial numbers increase due to less protozoal predation, one might expect minimal affects on fiber fermentation (Nelson et al., 2001). Interestingly, neither DMI (P = 0.16) nor diet digestibilities differed (P >0.42) between tallow- and RG-fed steers, indicating only minimal decreases in fiber fermentation due to dietary fat addition. Fat addition should, therefore, increase diet energy content and steer growth performance.
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. Dry matter intake was not (P >0.20) affected by diet and averaged 8.2 ± 0.17 kg/d. Even though DMI has been reported to decrease when fat is fed, this decrease is normally transient (Krehbiel et al., 1995; Ludden et al., 1995; Plascencia et al., 1999). Average daily gain (1.48 to 1.60 ± 0.03 kg/d) and G:F (0.184 to 0.202 ±0.006) increased linearly (P <0.05) as RG increased in the diet; steers fed tallow did not differ (P = 0.15) from those fed RG at the same level of fat and AH. These effects of dietary fat on ADG and G:F are consistent with those reported by Brandt and Anderson (1990), Bartle et al. (1994), and Plascencia et al. (1999).
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reported 6.2 and 4.5, and Zinn (1989) reported 5.8 and 4.6 Mcal of NEm/kg DM and Mcal of NEg/kg DM, respectively. Also calculated by difference, tallow contained 3.7 Mcal of NEm/kg DM and 2.8 Mcal of NEg/kg DM. Nelson et al. (2001) measured tallow ME in barley finishing diets fed to sheep to average 4.7 Mcal of ME/kg. At 5% of a finishing diet, Plascencia and Zinn (2001) found that RG and tallow were equal in energy value and averaged 6.0 and 4.8 Mcal of NEm and NEg/kg, respectively. Using the equation of Garrett (1980), tallow would contain 3.4 Mcal of NEm/kg and 2.5 Mcal of NEg/kg. Thus, the energy value of supple-mental fat is affected by interactions of fat with diet components, ruminal fermentation, and postruminal digestion (Nelson et al., 2001), and also seems to vary due to type and source.
Supplemental fat decreases fiber fermentation (Palmquist and Jenkins, 1980; Nelson et al., 2001), in vitro methane production (Czerkawski, 1973), and in vivo methane emission (Nelson et al., 2001). Additionally, total-tract fatty acid digestibilities of this tallow were substantial (Nelson et al., 2001), as were those of RG (Zinn, 1989). Minimum fiber digestion was noted with 4% tallow, but minimum methane emission was noted with 6% tallow in barley-finishing diets fed to wethers (Nelson et al., 2001). Therefore, inclusion of 3% RG may have substantially decreased fiber digestion, but not methane emission, such that diet energy content was not increased even though on d 93 and 94, fiber digestion was not greatly decreased.
Carcass Traits.
Hot carcass weight was increased linearly (P <0.01) by level of RG from 344 to 351 ± 2.9 kg, and the percentage of kidney, pelvic, and heart fat also increased (P >0.01) linearly by level of RG from 2.1 to 2.4 ± 0.06% (Table 4
). Numerous studies have shown similar responses to fat supplementation, including Brandt and Anderson (1990), Plascencia et al. (1999), and Plascencia and Zinn (2001). However, Plascencia and Zinn (2001) noted substantially more kidney, pelvic, and heart fat in carcasses of tallow- than RG-fed steers, which was not the case in the current study. All carcasses were A-maturity (results not shown), and LM area (86.9 ± 0.58 cm2) was not affected (P >0.10) by diet. Percentage of carcasses with a yield grade of 3, 4, and 5 increased linearly (P = 0.09) with RG level, averaging 17, 22, and 34 ± 3.7% for 0, 3 and 6% RG, respectively (results not shown).
There were RG xAH interactions for 12th-rib fat thickness and yield grade (linear; P <0.05), as well as marbling score and percentage of carcasses grading U.S. Choice (quadratic; P <0.05). Fat thickness and yield grade increased with RG in 3.5%, but not 7%, AH diets. Marbling scores and percentage of carcasses grading USDA Choice were maximized in 3.5% AH diets, but were minimized in 7% AH diets that contained 3% RG. Steers fed tallow had lower (P = 0.01) marbling scores (372 vs. 395 ± 5.54; 300 to 399 = slight marbling), and a lower (P = 0.07) percentage of U.S. Choice carcasses (20.8 vs. 42.8 ± 7.71%) than those fed RG. This result is in contrast to the findings of Plascencia and Zinn (2001), who noted no differences in marbling due to fat source. The reported effects of fat supplementation on fat thickness and marbling score are somewhat contradictory. For example, fat did not affect either fat thickness or marbling score in Zinn (1988), increased only marbling in Zinn (1989), increased only fat thickness in Boch et al. (1991), and increased fat thickness but decreased marbling in Clary et al. (1993). However, Huffman et al. (1992) noted a tallow level xforage level interaction, where fat thickness was increased by feeding a diet containing 6% tallow and 7.5% forage, but not with a diet containing 6% tallow and 0% forage; however, there were no dietary effects on quality grade.
A quadratic RG xAH interaction (P <0.01) was detected for beef color score, which was minimized in the LM of steers fed 3.5% AH diets but was maximized in 7% AH diets that contained 3% RG. Diet did not (P >0.21) affect beef brightness score (2.5 ± 0.06) or beef texture score (2.6 ±0.05). Beef firmness score was decreased linearly (P <0.05) by RG, averaging 3.0, 2.8, and 2.7 ± 0.04 for 0, 3, and 6% RG, respectively. Additionally, beef firmness score tended to be greater (P = 0.08) for 6% tallow-fed than 6% RG-fed steers (2.7 vs. 3.0 ± 0.10). These results suggest that i.m. fat content (marbling) decreased beef color and firmness scores, and that beef fat from RG-fed steers may contain a greater proportion of unsaturated fatty acids than tallow-fed steers.
Fat color score was not (P >0.18) affected by diet (3.0 ± 0.07); however, fat luster scores decreased linearly (P <0.05) with RG, averaging 3.1, 2.8 and 2.8 ± 0.05 for 0, 3, and 6% RG, respectively (Table 4). These results suggest that the level of AH (carotenoids) did not affect fat color but RG decreased fat luster, possibly by changing the fatty acid composition (Marks et al., 2004).
Moisture Retention Properties.
A linear RG xAH interaction (P <0.05) was detected for wholesale cut purge. Purge decreased as level of RG increased in diets containing 3.5% AH, whereas purge increased linearly (0.4 to 0.9%) as RG level increased in diets containing 7% AH (Table 5), possibly due to less saturated fatty acid content. There was a quadratic RG xAH interaction (P <0.05) for LM pH. For diets containing 3.5% AH, pH was highest with 3% RG, but not 7.0% AH, whereas pH was minimized with 3% RG; however, all dietary treatment means for pH were between 5.55 and 5.60 ± 0.01 (Table 5). The small but statistically significant effect of diet on wholesale purge could not be explained by pH because a lower pH would generally be associated with greater water loss (Hedrick et al., 1989). In this case, dietary treatments with the least and most wholesale purge had the same pH. Moreover, drip loss (3.0 ± 0.08%), thaw drip loss of a vacuum-packaged steak (2.6 ±0.22%), and retail purge score (1.8 ±0.05%) were not affected (P >0.10) by diet. Thus, dietary treatment did not seem to result in biologically important differences in moisture retention properties. As expected, panelists’ scores for amount of purge in retail packages increased (P <0.05) from 1.1 to 2.3 ± 0.07% during retail storage (Table 6).
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) was not affected (P >0.16) by diet (4.2 ± 0.04); however, color score decreased quadratically (P <0.001) from 5.1 to 3.5 ± 0.04 during retail storage (Table 6). A quadratic RG xAH interaction (P <0.05) was detected for L* values, with the highest L* values for steaks of steers fed 3% RG and 7% AH, and the lowest for steaks of steers fed 3% RG and 3.5% AH. Steaks from steers fed RG had higher (P <0.05) L* and b* values than steaks from tallow-fed steers, indicating that, throughout storage, LM color was lighter and more yellow than steaks from steers fed tallow. However, these differences in objective color measurements were not detected by the trained color panel (P >0.16). Treatment means for marbling scores (Table 4) and ether-extractable i.m. fat content (Marks et al., 2004) followed the same general pattern, indicating that marbling may have increased meat brightness (L* values) and yellowness (b* values); however, trained panelists would have ignored the marbling and based their score just on the lean color. Overall, dietary effects on color attributes of LM steaks were small, may have been caused by differences in marbling, and are likely of little practical importance to the beef industry.
Cooking Attributes, WBSF, and Trained Sensory Panel.
Cooking time, cooking loss, and WBSF were not affected (P >0.12) by dietary treatment, with overall mean values of 29.6 ± 0.49 min, 28.8 ±0.94%, and 4.1 ±0.08 kg, respectively (Table 5). Shear force values were slightly higher than expected compared with trained panel scores. In Busboom et al. (2000), mean WBSF values were lower than for the current study (3.5 vs. 4.1 kg), whereas trained sensory panel tenderness scores were slightly lower than in the current study (6.5 vs. 7.1 on a 10-cm line scale). The most likely reason for this apparent discrepancy is that an average of four cores from the lateral half of the LM were used in this study instead of the six cores from the whole muscle used by Busboom et al. (2000). Berry (1993) reported that there was a definite tenderness gradient within beef LM steaks, and the most lateral cores had the highest shear values. Trained sensory panel sustained tenderness (6.7 ± 0.11), initial juiciness (6.9 ±0.14), sustained juiciness (5.6 ±0.16), and beef flavor intensity (5.3 ±0.12) scores were not affected (P >0.10) by dietary treatment, and off-flavor score was not affected (P = 0.25) by type of supplemental fat. However, initial tenderness increased quadratically (P = 0.07) from 7.1 to 7.4 ± 0.08 with increasing dietary RG. There was a linear RG xAH interaction (P <0.05) for off flavor. Off flavor did not change with RG in diets containing 3.5% AH diets, but off-flavor decreased for 7.0% AH diets with increasing RG in the diet. Thus, there was a slight tendency for off flavor to be reduced by dietary RG but this effect has quite small and probably of limited importance.
Altering the fatty acid composition of beef muscle can affect beef flavor (Ford et al., 1976). Linoleic acid (C18:2) and 
-linolenic acid (C18:3) have major effects on beef flavor (Larick et al., 1987; Larick and Turner, 1990). Beef flavor has been reported to be negatively correlated to stearic (Melton et al., 1982a,b) and linolenic (Melton et al., 1982a,b; Mandell et al., 1998) acid, but positively correlated to myristic (Larick and Turner, 1990), palmitic (Larick and Turner, 1990), palmitoleic (Melton et al., 1982a,b; Larick and Turner, 1990), and oleic (Larick and Turner, 1990; Mandell et al., 1998) acids. Of the fatty acids that could negatively influence palatability, stearic acid was increased by 1.4 g/100 g of fatty acid by RG, but linolenic acid content was not affected by level of RG (refer to Marks et al., 2004). Of the fatty acids positively related to palatability, myristic was increased only 0.5 g/100 of fatty acid by RG. Diet did not affect palmitic acid, and an RG xAH interaction was detected on palmitoleic due to small changes in composition. Oleic was 2.5 g/100 g of fatty acid lower in beef from steers fed tallow compared with RG (Marks et al., 2004). Nonetheless, these potential negative and positive influences of fatty acid composition on palatability were quite small and were not detected by the sensory panel.
Wood and Enser (1997) concluded that increased unsaturated fatty acid content increased susceptibility of meat to oxidation, and that increased dietary vitamin E would be needed to prevent flavor deterioration due to lipid oxidation. Further, Elmore et al. (1999) suggested that autoxidation of fatty acids in meat was initiated by greater quantities of n-3 fatty acids, notably linolenic acid. Even though fatty acid composition of beef in the current study was altered by dietary fat (refer to Marks et al., 2004), substantial vitamin E was fed (Table 1), and the linolenic acid content was small and not affected by dietary treatment (Marks et al., 2004). Therefore, we did not expect differences in beef flavor nor off flavor due to changes in fatty acid content or composition.
Therefore, RG increased diet energy content, which improved rate and efficiency of gain, and increased carcass fatness. Compared with tallow, RG increased marbling and the percentage of carcasses grading USDA Choice, or higher, but slightly decreased lean firmness and fat luster scores. Furthermore, relatively few minor effects of diet on moisture retention and retail storage properties, WBSF, or sensory panel scores were detected; thus, it can be concluded that up to 6% RG can be included in diets containing either 3.5% or 7% AH without detrimental effects on beef appearance and palatability compared with diets containing lower levels of RG or 6% tallow.
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3 Current address: Univ. of Wyoming Coop. Ext. Service, Jackson 83001-1708.
2 Correspondence: 235 Clark Hall (phone: 509-335-5623; fax: 509-335-4246; e-mail: nelsonm{at}wsu.edu).
Received for publication May 23, 2003. Accepted for publication August 30, 2004.
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