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J. Anim Sci. 2008. 86:936-948. doi:10.2527/jas.2007-0410
© 2008 American Society of Animal Science
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ANIMAL PRODUCTS

Effects of supplemental fat on growth performance and quality of beef from steers fed corn finishing diets1

M. L. Nelson*,2, J. R. Busboom*, C. F. Ross{dagger} and J. V. O’Fallon*

* Department of Animal Sciences, and and {dagger} Department of Food Science and Human Nutrition, Washington State University, Pullman 99164-6351


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
To measure the effects of dietary fat on feedlot performance and carcass characteristics, and on beef appearance, moisture binding, shelf life, palatability, and fatty acid content, 126 crossbred beef steers (321.1 ± 0.57 kg of BW) were allotted to a randomized complete block (3) design with a 3 x 2 + 1 factorial arrangement of dietary treatments. The main effects were level of yellow grease (0, 3, or 6%) and alfalfa hay (3.5 or 7%) in corn-based diets containing 15% potato by-product (PB). The added treatment was 6% tallow and 7% alfalfa in a barley-based diet containing 15% PB. Dry matter intake and ADG were not affected by diet; however, G:F and diet NE content increased linearly (P < 0.10) with yellow grease. Kidney, pelvic, and heart fat (2.0 to 2.3 ± 0.07) and yield grade (2.8 to 3.1 ± 0.09) increased linearly (P ≤ 0.05) with yellow grease. Steers fed corn plus 6% yellow grease had lower (P < 0.05) beef firmness and beef texture scores but greater (P < 0.01) fat color score than those fed barley plus 6% tallow. Moisture retention of beef was not affected by dietary treatment, except purge score during retail storage, which was decreased linearly (P < 0.01) from 2.1 to 1.6 ± 0.06 by level of yellow grease. Steaks from steers fed barley plus 6% tallow had greater (P < 0.05) shear force than those from steers fed corn plus 6% yellow grease, and beef flavor increased linearly (P < 0.05) from 6.2 to 6.7 ± 0.11 as the level of yellow grease increased. Level of yellow grease linearly increased (P < 0.01) transvaccenic acid (TVA) by 61% and CLA content of beef by 48%. Beef from steers fed corn plus yellow grease had lower (P < 0.05) palmitoleic and oleic acids and greater (P < 0.05) linoleic, TVA, and CLA than beef from steers fed the barley-tallow diet. Feeding yellow grease increased diet energy content, which increased carcass fatness, and altered beef fatty acid content, which increased beef flavor without affecting moisture retention, shelf life, or cooking properties of the beef. Additionally, beef from steers fed corn plus 6% yellow grease was more tender and had more polyunsaturated fatty acid content and CLA than beef from steers fed barley plus 6% tallow.

Key Words: beef cattle • conjugated linoleic acid • fatty acid • transvaccenic acid • yellow grease


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
Finishing cattle synthesize substantial quantities of lipid, which has been extensively studied due to its relationship with human health. Recently, numerous studies have identified methods to increase CLA, MUFA, and PUFA in beef tissue. Most studies fed supplemental fat high in linoleic acid, which increased total fat and CLA without increasing CLA proportion (e.g., Mir et al., 2002Go, 2003Go). However, our laboratory, Marks et al. (2004)Go increased content of CLA in beef by 42% without an increase in fat content [143 ± 5.2 mg of fatty acid (FA)/g of DM] by feeding steers a barley-based diet supplemented with up to 6% yellow grease (YG).

Beef shelf-life stability and palatability may be affected by feeding a high-linoleic acid fat to steers to increase CLA content. Yellow restaurant grease is higher in unsaturated 18C FA than tallow (Nelson et al., 2004Go). Although several studies determined the impact of YG or tallow on feedlot performance (Zinn, 1988Go; Plascencia et al., 1999Go; Plascencia and Zinn, 2001Go), our studies (Marks et al., 2004Go; Nelson et al., 2004Go) evaluated the effects of YG and tallow on beef quality and palatability attributes from steers fed barley-based diets. To our knowledge, no other published study is available with corn-based diets, which would be higher in ether extract and NE, but lower in NDF, which could alter ruminal fermentation, biohydrogenation, and beef composition and palatability.

Therefore, the objective of this study was to determine effects of YG and forage level in corn-based finishing diets on feedlot performance, beef appearance and shelf life, carcass characteristics, beef composition, and beef palatability.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 LITERATURE CITED
 
This experimental protocol was approved by the Washington State University Animal Care Committee. All procedures conformed to the Guide for the Care and Use of Agricultural Animals in Research and Teaching (FASS, 1999Go).

Animals and Feeding
One hundred twenty-six crossbred steer calves (321.1 ± 0.57 kg of BW) 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 Ralgro (Schering-Plough Corp., Kenilworth, NJ). Steers were blocked by BW (obtained on 2 consecutive days, each after a 12-h fast) into 3 blocks and assigned randomly within each block to 1 of 7 pens (6 steers per pen). Each pen was 4.9 x 15.2 m, with a roof that covered the feed bunk plus 5 m of the pen. Pens, within block, were assigned randomly to dietary treatments in a 3 x 2 + 1 factorial arrangement. Main effects were level of YG (0, 3, or 6%) and level of alfalfa hay (AH; 3.5 or 7.0%) in corn-based diets, with an added treatment of 6% tallow with 7.0% AH in a barley-based diet (all dietary levels are expressed on a DM basis). The added treatment was a treatment in common with the study of Marks et al. (2004)Go and Nelson et al. (2004)Go to aid in comparisons and for our use in modeling.

Corn and Baronesse barley were 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 YG or tallow (Baker Commodities, Spokane, WA), respectively, was sprayed onto the steam-rolled corn or barley in a horizontal mixer.

Steers were adapted over a 20-d period to the final diets containing 0, 3, or 6% YG in corn-based diets or 6% tallow in the barley-based diet, 15% PB, 7% supplement (Table 1Go), and 3.5 or 7.0% AH on a DM basis. Steers were fed (DM basis) diets of 42.5% grain plus fat, 40% alfalfa, 7.5% PB, and 17% supplement for 10 d, and then diets of 58% grain plus fat, 20% alfalfa, 15% PB, and 7% supplement for the last 10 d of adaptation. Supplemental fat was increased in 3-percentage-unit increments in each of the 2 adaptation diets for steers fed the final finisher diet containing 6% YG or tallow. Diets were formulated to meet or exceed the nutrient requirements of steers (NRC, 1996Go) and contained (DM basis) at least 13.0% CP, 0.52% Ca, 0.26% P, 0.15% S, 0.65% K, 0.10% Mg, 8.7 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; Tylan and Rumensin were purchased from Elanco Animal Health, Greenfield, IN).


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  		Table 1. Composition of supplement fed at 7% of diet DM
 
Steers were pen-fed once daily, in amounts such that the bunks were empty just before feeding, using a Data Ranger (American Calan, Northwood, NH). Individual steer BW, without water or feed restriction, were measured at 28-d intervals. To determine diet digestibilities, fecal grab samples were obtained from all steers on d 116, 117, and 118. Fecal samples were dried in a forced-air oven (50°C), composited within pen (wt/wt), and ground to pass a 1-mm screen in a Wiley mill (Arthur H. Thomas Co., Philadelphia, PA). To determine feed intake, daily feed offered and orts were weighed, and subsamples of diet and orts were collected from d 114, 115, and 116. Acid-insoluble ash was used as the internal marker for determining apparent digestibilities (Van Keulen and Young, 1977Go).

Final steer BW for calculation of ADG and G:F were HCW divided by 63% (standard dressing percentage). The NEm and NEg concentrations of the diets were calculated iteratively (Zinn and Owens, 1993Go) using the relationships NEg = (0.877 NEm) – 0.41 (NRC, 1996Go), energy gain (Mcal/d) = (0.0557 BW0.75) x ADG1.097 (NRC, 1996Go), and NEm (Mcal/d) = 0.077 BW0.75 (Lofgreen and Garrett, 1968Go). The NEm and NEg contents of YG were calculated by difference (Schneider and Flatt, 1975Go) using NEm and NEg values from the NRC (1982Go, 1996)Go. The NEm and NEg contents of tallow were calculated from the diet NEm and NEg content using feed energy values from the NRC (1982Go, 1996)Go.

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 samples (except for YG and tallow) were analyzed for DM (oven drying at 50°C), OM (ashed at 600°C for 6 h), CP using a Leco (St. Joseph, MI) FP-528 Protein/ Nitrogen Determinator (AOAC, 1990Go; method 990.03), crude fat using a Leco TFE2000 Fat Extractor (AOAC, 1990Go; method 920.39), NDF (procedure A), ADF, and ADL according to Van Soest et al. (1991)Go, and feed samples were analyzed for starch content following the procedure of Åman and Hesselman (1984)Go.

Moisture, insoluble matter, unsaponifiable matter, and fat color were measured on YG and tallow (AOCS, 1990Go). Whole corn and barley samples, after cleaning, were measured for volume-weight and kernel size distributions. Broken kernels and foreign material were defined as readily passing through an aluminum sieve (Seedburo Equipment Co., Chicago, IL) 0.81-cm thick with round holes 0.476 cm in diameter and that were 0.635 cm apart (USDA, 1975Go). Plump barley kernels were defined as kernels retained on a 0.24- x 1.91-cm sieve (Seedburo Equipment Co.), medium kernels were retained on a 0.20- x 1.91-cm sieve, and thin kernels passed through a 0.20- x 1.91-cm sieve (USDA, 1975Go).

Steam-rolled corn and barley samples were separated using tared, Tyler, standard, screen scale sieves (W.S. Tyler Co., Cleveland, OH), with 7,650-, 4,760-, 1,981-, 991-, 495-, 246-, and 124-µm openings with a bottom pan. Samples were dry sieved by being placed on the top sieve and shaken in a mechanical horizontal-plane shaker until equilibrium of weight retained was reached (Nelson, 1988Go). Dry sieving was selected as the method of choice because Van Soest (1994)Go 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 the 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 of mean particle size (log10 µ) and log10 of the standard SD (log10 {sigma}) were estimated by –a/ b and 1/b, respectively (Waldo et al., 1971Go).

Carcass Data Collection and Muscle Sampling
The heaviest block of steers was slaughtered after 134 d on feed, and the medium and the lightest blocks were slaughtered after 155 d on feed. Steers were shipped 320 km from the feedlot to a commercial plant, where they were humanely slaughtered on 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 KPH, marbling and maturity scores, and quality grades (USDA, 1996Go), 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, 1988Go) were obtained by 4 trained university personnel.

Longissimus Muscle Sampling
A boneless strip loin roast was removed from the left side of 3 randomly selected carcasses per pen (63 total). Strip loins were removed beginning at the 13th rib and continuing to a horizontal cut made 15.3 cm caudal 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 cranial end, one 1.3-cm-thick, a second 1.3-cm-thick, and then three 2.5-cm-thick steaks were sliced. The first steak was used for determination of FA composition, the three 2.54-cm-thick 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. The LM slice was trimmed of all surrounding fat and connective tissue. Then, muscle slices and fat samples were cut into approximately 1.3 x 1.3 x 1.3-cm cubes, placed in separate Whirl-Pak bags (Nasco, Ft. Atkinson, WI), and stored at –20°C under an N2 atmosphere for up to 6 wk. After lyophilization, the samples were ground with dry ice in a coffee bean grinder (Mr. Coffee Inc., Cleveland, OH). Dry matter was determined, and samples were stored in a –20°C freezer in plastic bottles under an N2 atmosphere for subsequent CP, ether extract, and FA analysis.

Chemical Analyses
Crude protein and crude fat contents of muscle samples were determined by AOAC (1990)Go methods 990.03 and 920.39, respectively. These analyses were run in duplicate, and the results were reported on a DM basis.

Fatty Acid Analyses
Meat samples (after lyophilization) were ground in a coffee bean grinder, and ground feed samples were hydrolyzed for 1.5 h at 55°C in 1 N KOH in methanol containing C13:0 as an internal standard, neutralized, and the FA methylated by H2SO4 catalysis for 1.5 h at 55°C (O’Fallon et al., 2007Go). Methyl esters of FA were extracted in hexane and quantified by capillary gas chromatography on a SP-2560, 100 m x 0.25 mm x 0.20 µm capillary column Supelco, Bellefonte, PA) on a Hewlett Packard 5890 gas chromatograph (Hewlett Packard, Farmington Hills, MI) equipped with a Hewlett Packard 3396 Series II integrator and 7673 controller, a flame-ionization detector, and split injection. Initial oven temperature was 140°C, which was held for 5 min and then increased to 240°C at 4°C/min and held for 20 min. Helium was the carrier gas at 0.5 mL/min, and the column head pressure was 2.8 kg/cm. Injector and detector temperatures were 260°C. The split ratio was 30:1. Fatty acids were identified by comparing their retention times to those of methylated FA standards (Nu-Chek Prep Inc., Elysian, MN; Supelco, Bellefonte, PA).

We have shown that this method (O’Fallon et al., 2007Go) does not introduce FA artifacts, including isomerization to CLA, and methylates both esterified and free FA. Further, we recover approximately 92% of the ether extract weight as FA. Therefore, this method is preferable to methylation with either sodium methoxide or boron trifluoride. Fatty acid composition of LM, including trans-vaccenic acid (TVA), was independently verified by D. C. Rule (University of Wyoming, Laramie, personal communication), who used the methods described by Murrieta et al. (2003)Go and Lake et al. (2007)Go.

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-Pak bag, and suspended in a 1°C cooler. After 24 h, the sample was reweighed to determine percentage loss (Nelson et al., 2000Go). Thaw drip loss was determined on steaks used for WBSF using procedures similar to those used 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 homogenizing a 5-g (wet weight) sample in 20 mL of distilled water with a polytron homogenizer (Brinkman Instruments, Westbury, NY).

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, 4-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, 1991Go) 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 were allowed for both color and purge panel scores. 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 6 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 procedures (AMSA, 1995Go). 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 percentage cooking loss was determined. Eight 1.27-cm cores from 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., 1997Go). For statistical analysis, the values of the 8 cores were averaged.

Steaks for trained panel analysis were thawed and cooked as described for WBSF. After cooking, external fat and major connective tissue was removed. Cooked steaks were cut into 1.0- x 1.0- x 2.5-cm pieces, and samples were served immediately to an 8-member trained sensory panel (AMSA, 1995Go). Panelists used a 10-cm unstructured line labeled at each end (Stone and Sidel, 1985Go) 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 the panelists’ scores and the results were expressed in centimeters along an unstructured line scale.

Statistical Analysis
Data, except for simulated retail display, were analyzed as a randomized complete block design with a 3 x 2 + 1 factorial arrangement of dietary treatments using the GLM procedure (SAS Inst. Inc., Cary, NC). Pen was the experimental unit for all analyses. Main effects were level of YG (0, 3 or 6%) and level of AH (3.5 or 7.0%) in a corn-based diet, with the added treatment of 6% tallow with 7.0% AH in a barley-based diet. Least squares means were separated by preplanned contrasts for linear and quadratic effects of level of YG, AH level, YG x AH, and corn plus 6% YG vs. barley plus 6% tallow with 7.0% AH (Steel and Torrie, 1980Go). Simulated retail display data were analyzed as a repeated-measures design (Gill and Hafs, 1971Go), with the whole plot arranged as described above and display day as the subplot. Linear, quadratic, and cubic contrasts for display day were calculated. The treatment x block interaction (12 df) was used to test the whole plot, whereas residual error (56 df) was used to test the subplot.


   RESULTS AND DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
LITERATURE CITED
 
Feedstuff Description and Composition
Volume-weights of whole barley and corn averaged 67.1 and 72.6 kg/hL on an air-dry basis. The corn contained 0.3% broken corn and foreign material and 0.2% heat-damaged kernels. The corn was US No. 1 (USDA, 1975Go). Volume-weights of steam-rolled barley and corn averaged 51.5 and 57.6 kg/hL on an air-dry basis. The proportion of plump, normal, and thin barley kernels averaged 94.7, 14.4, and 0.9%, respectively. Black kernels averaged 0.01%, and the barley was US No. 1 (USDA, 1975Go). Steam-rolled barley and corn sieve data seemed to adequately fit the logarithmic normal distribution (Waldo et al., 1971Go). For barley, mean r2 value was 0.99, skewness value was 0.24, and kurtosis value was –0.837. Average log10 µ value was 1.12 and log10 {sigma} value was 5.75 for steam-rolled barley. Particle size distribution for steam-rolled barley was larger than that of Baronesse barley (Nelson et al., 2000Go) and Camelot barley (Nelson et al., 2001Go) due to the high proportion of plump kernels. For corn, mean r2 value was 0.97, skewness value was 0.33, and kurtosis value was –1.30. Average log10 µ value was 8.91 and log10 {sigma} value was 2.42. Particle size was also larger than steam-rolled corn of Nelson et al. (2000)Go.

The barley (Table 2Go) had similar CP, starch, and ash values, and similar but lower NDF values compared with those reported by Duncan et al. (1991)Go, by NRC (1984)Go for Pacific coast barley, and by NRC (1996)Go for heavy barley grain. The PB (Table 2Go) contained less CP than NRC (1984)Go, and less CP and ADF but greater starch compared with previous studies from our laboratory (Duncan et al., 1991Go; Nelson et al., 2000Go). The AH used in this study was similar in composition to mid-to late-bloom alfalfa in NRC (1996)Go.


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  		Table 2. Composition of feedstuffs
 
Total FA content of barley and AH was similar or greater to the FA content of these feedstuffs reported by Palmquist (1988)Go and Nelson et al. (2001)Go but greater than that of Nelson et al. (2004)Go. Barley FA were similar to those measured by Palmquist (1988)Go and Miller et al. (1996)Go, but contained no C16:0 and less C18:2 than previous studies by Nelson et al. (2000Go, 2004)Go. The FA content and composition of tallow was similar to Palmquist (1988)Go, and similar to the tallow and YG reported by Grummer and Klopfenstein (1996)Go and Nelson et al. (2004)Go except for lower oleic acid content. The PB contained less total FA, palmitic and oleic acids but more vaccenic acid than Nelson et al. (2004)Go. Alfalfa FA contained similar C16:0, C18:0, and C18:3, but less C18:2 than that reported by Palmquist (1988)Go and Nelson et al. (2001)Go but more C18:3 than reported by Nelson et al. (2004)Go. Our procedure for FA analyses (O’Fallon et al., 2007Go) gave greater FA recovery and improved peak separation and identification compared with the procedure we used in Marks et al. (2004)Go, which undoubtedly contributed to some of these differences. The FA content of the control diet was low (3.8%); thus, FA deposited in muscle tissue would be largely from de novo FA synthesis and smaller amounts from microbial synthesis. Tallow and YG contained 0.2 and 0.94% moisture, <0.01 and 0.41% insoluble matter, 0.32 and 0.44% unsaponifiable matter, and fat advisory committee color of 15 and 21, respectively.

Diet Digestibilities
On d 116, 117, and 118, the level of YG linearly decreased (P < 0.05) DMI from 10.6 to 9.2 ± 0.32 kg/d probably due to diet energy content (Table 3Go). Linear YG x AH interactions were detected (P < 0.05) for digestibilities of DM, OM, cell solubles, NDF, and hemicellulose. These interactions were due to increased AH decreasing digestibility in diets containing YG. This was most likely due to encrusting of fiber or decreased gram-positive bacteria in the rumen. The corn plus 6% YG diet was more digestible (P < 0.01) than the barley plus 6% tallow diet (85.7 vs. 79.6 ± 1.09% cell soluble digestibility, respectively) but had decreased (P < 0.01) NDF and hemicellulose digestibility compared with the barley plus 6% tallow diet. Level of YG linearly increased (P < 0.05) ADF digestibility and quadratically increased (P < 0.05) GE digestibility. In contrast, Nelson et al. (2004)Go noted increasing dietary YG linearly decreased (P < 0.01) hemicellulose digestibility in barley-based diets and YG did not differ from tallow addition on diet digestibilities. Even though fat addition has been shown to decrease fiber fermentation (Ikwuegbu and Sutton, 1982Go; Jenkins and Palmquist, 1984Go; Nelson et al., 2001Go), evidence exists that fat does not decrease fiber fermentation by coating fiber particles (Ørskov et al., 1978Go; Drackley et al., 1994Go; Mir, 1998Go). Numerically, the barley plus 6% tallow diet had greater NDF and hemicellulose digestibilities than the control diet containing 7% AH and were much greater than the comparable diet in Nelson et al. (2004)Go. This appears to be due to greater barley fiber digestibility in the current study.


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  		Table 3. Feed intake and diet digestibilities of steers fed corn plus yellow grease or barley plus tallow finishing diets
 
Feedlot Performance
Dry matter intake (9.2 ± 0.20 kg/d) and average daily gain (1.65 ± 0.05 kg/d) were not affected (P > 0.21) by diet (Table 4Go). However, gain to feed (0.175 to 0.188 ± 0.005) and diet NEm and NEg contents increased linearly (P = 0.09 and P = 0.08, respectively) as YG increased from 2.2 to 2.3 ± 0.05 Mcal/kg and from 1.5 to 1.6 ± 0.04 Mcal/kg, respectively. Effects of fat on DMI is normally transient (Krehbiel et al., 1995Go; Ludden et al., 1995Go; Plascencia et al., 1999Go; Nelson et al., 2004Go). The barley plus 6% tallow diet averaged 2.32 Mcal of NEm/kg of DM and 1.62 Mcal of NEg/kg of DM, which did not differ (P > 0.10) from the corn plus 6% YG diet at the same AH level. Similarily, digestibility of GE did not differ (P > 0.25) between the corn plus 6% YG diet and the barley plus 6% tallow diet (Table 3Go). Calculated by difference using NEm and NEg values from NRC (1996)Go and NRC (1982)Go, YG contained 4.6 Mcal of NEm/ kg of DM and 3.7 Mcal of NEg/kg of DM at 6% of the diet. These values are similar to vegetable oil in NRC (1996)Go but less than the 5.7 to 6.2 Mcal of NEg/kg of DM and 4.5 to 5.0 Mcal of NEg/kg of DM reported by Zinn (1988)Go, Zinn (1989)Go, and Nelson et al. (2004)Go. Tallow contained 8.5 Mcal of NEm/kg of DM and 6.4 Mcal of NEg/kg of DM (calculated), which was greater than the 6.0 Mcal of NEm/kg of DM and 4.5 to 4.8 Mcal of NEg/kg of DM reported by NRC (1996)Go, Plascensia and Zinn (2001), and Nelson et al. (2004)Go. Additionally, Nelson et al. (2001)Go measured tallow ME in barley finishing diets fed to lambs to average only 4.7 Mcal of ME/kg of DM. Clearly, the energy value of supplemental fat is affected by interactions of fat with diet components, ruminal fermentation, and postruminal digestion (Nelson et al., 2001Go) and also varies due to type and source (Nelson et al., 2004Go).


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  		Table 4. Feedlot performance and on characteristics of the carcass, beef, and fat of steers fed corn plus yellow grease or barley plus tallow finishing diets
 
Carcass Characteristics
Most carcass characteristics were not affected (P > 0.11) by diet except KPH (2.0 to 2.3 ± 0.07) and yield grade (2.8 to 3.1 ± 0.09), which increased linearly (P < 0.05) as YG increased. Numerous studies have shown increased KPH fat due to supplemental dietary fat including Brandt and Anderson (1990)Go, Plascencia et al. (1999)Go, Plascencia and Zinn (2001)Go, and Nelson et al. (2004)Go. However, Plascencia and Zinn (2001)Go noted substantially more KPH in carcasses of steers fed tallow than in those fed YG, which was not observed in the current study or in Nelson et al. (2004)Go. Contradictory results have been reported for the effects of fat supplementation on carcass fat thickness and marbling score. For example, fat did not affect either fat thickness or marbling score in Zinn (1988)Go, increased only marbling in Zinn (1989)Go, increased only fat thickness in Boch et al. (1991)Go, and increased fat thickness but decreased marbling in Clary et al. (1993)Go. However, fat x forage level interactions were noted in Huffman et al. (1992)Go, in which fat thickness increased with increased tallow in 17.5% but not 0% forage-containing diets and Nelson et al. (2004)Go, in which fat thickness and yield grade increased with YG in 3.5% but not 7% AH diets. Quality grade was not affected by fat or forage level in Huffman et al. (1992)Go but was maximized in 3.5% AH diets and minimized in 7% AH diets that contained 3% YG in Nelson et al. (2004)Go. In the current study, marbling score did not differ (P > 0.17) between the corn plus 6% YG and the barley plus 6% tallow diets in contrast to lower marbling score in steers fed the tallow diet than those fed the YG diets in Nelson et al. (2004)Go. All carcasses were A– maturity (results not shown) and maturity was not affected by treatment (P > 0.48).

Carcass Beef and Fat Characteristics
Beef brightness score (2.9 ± 0.18) was not affected (P > 0.11) by diet. However, steers fed 6% YG and 7% AH had lower (P < 0.05) beef firmness and beef texture scores (2.8 vs. 3.0 and 2.6 vs. 3.0, respectively) but greater (P < 0.01) fat color scores than those fed the barley plus 6% tallow diet (3.1 vs. 2.7 and 3.2 vs. 2.9, respectively). Quadratic YG x AH interactions (P < 0.05) were detected for beef color score, beef firmness score, and fat color score because of very small numeric changes. Fat luster score was quadratically affected (P < 0.10) by YG level and was increased (P < 0.10) by AH level because of small numeric changes that were probably not biologically important. These differences between steers fed the corn plus 6% YG, 7% AH and those fed the barley plus 6% tallow are similar to those in Nelson et al. (2004)Go and both suggest that fat from YG-fed steers may contain a greater proportion of unsaturated FA than the steers fed barley plus 6% tallow, and the level of AH carotenoids did not affect fat color but corn carotenoids did.

Moisture Retention Properties
Moisture retention of beef was not affected by dietary treatment (Table 5Go) except that purge score during retail storage was linearly decreased (P < 0.01) by YG from 2.1 to 1.6 ± 0.06. Wholesale cut purge (1.2 ± 0.11%), pH (5.6 ± 0.01), drip loss (0.6 ± 0.04%), and thaw drip loss of a vacuum-packaged steak (5.3 ± 0.25%) were not affected (P > 0.10) by diet. As expected, panelists’ scores for amount of purge in retail packages quadratically increased (P < 0.01) from 1.2 to 2.2 ± 0.04% during retail storage (Table 6Go), almost identically to those of Nelson et al. (2004)Go. Dietary effects on moisture retention properties of steaks were small.


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  		Table 5. Moisture retention, color, cooking, and palatability attributes of beef of steers fed corn plus yellow grease or barley plus tallow finishing diets
 

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  		Table 6. Purge score, color score, and L*, a*, b* values during retail storage of beef of steers fed corn plus yellow grease or barley plus tallow finishing diets
 
Retail Color Score and L*, a*, and b* Values
Retail color score (5.0 ± 0.02), L* (45.0 ± 0.88), a* (24.0 ± 0.46), and b* (19.6 ± 0.08) were not affected (P > 0.10) by diet (Table 5Go). Steaks in the current study were slightly more cherry red color and darker (L*) but similar red color (a*) and yellow color (b*) to those of Nelson et al. (2004)Go. During retail storage, color score quadratically (P < 0.05) decreased (5.8 to 4.5 ± 0.02), L* linearly (P < 0.05) decreased (45.9 to 42.7 ± 0.74), a* linearly (P < 0.01) decreased (27.0 to 22.6 ± 0.42), and b* quadratically (P < 0.05) increased (19.3 to 19.6 ± 0.06) (Table 6Go). Steaks from the current study became browner at a similar rate, became darker at a faster rate, less red at a faster rate, but showed similar small changes in yellowness to steaks in Nelson et al. (2004)Go. Dietary effects on color attributes of steaks were small.

Cooking Attributes, Waner-Bratzler Shear Force, and Trained Sensory Panel
Cooking time, cooking loss, and WBSF were not affected (P > 0.22) by level of YG or AH or their interaction, which averaged 35.9 ± 2.28 min, 21.6 ± 0.67%, and 2.6 ± 0.06 kg, respectively (Table 5Go). Degree of doneness averaged medium and was not affected by treatment (P > 0.14; data not shown). Inexplicably, steaks from steers fed barley plus 6% tallow had greater (P < 0.05) shear force than those from steers fed corn plus 6% YG (3.1 vs. 2.6 ± 0.14 kg). However, dietary treatment did not affect (P > 0.23) sensory panel measurements (10-cm line scale) of initial tenderness (7.4 ± 0.16), sustained tenderness (7.2 ± 0.16), initial juiciness (6.5 ± 0.17), sustained juiciness (6.0 ± 0.15), or off-flavor (0.5 ± 0.06). Shear force values were lower than in Busboom et al. (2000)Go, and Nelson et al. (2004)Go, which was also shown in the trained sensory panel tenderness scores. Interestingly, beef flavor increased linearly (P < 0.05) from 6.2 to 6.7 ± 0.11 as dietary YG increased, suggesting altered FA content. Therefore, dietary YG had positive effects on beef quality but steaks from all dietary treatments were tender, juicy, and flavorful.

Longissimus Muscle Composition
As expected, fat, and total FA content of muscle were affected oppositely to DM and all had significant quadratic YG x AH interactions (Table 7Go). These interactions were mainly because of increased muscle fat and FAs with diets containing 6% AH with 3% YG. These results agree with the slightly greater energy intake, KPH, and marbling score of steers fed 7% vs. 3.5% alfalfa hay and 3% YG. Fatty acid composition of LM, in general, was similar to steers fed barley-potato byproduct diets (Nelson et al., 2000Go), canola-supplemented diets (Rule et al., 2002Go), or barley-potato byproduct diets with supplemental YG (Marks et al., 2004Go) except for lower stearic and linolenic acids but greater TVA (Table 7Go). However, specific FA were also altered by diet. Palmitoleic acid (C16:1) decreased linearly (P < 0.10) from 3.6 to 3.2 ± 0.11 g/100 g of FA with increased YG. Level of dietary YG linearly decreased (P < 0.01) margaric acid (C17:0) and 10-heptadececonic acid (C17:1) from 1.8 to 1.6 ± 0.04 and 1.4 to 1.2 ± 0.04, respectively, even though intake of these FA would have increased, suggesting either dilution due to increased even-chain FA or decreased odd-chain FA synthesized from propionate (Marks et al., 2004Go). The level of YG linearly increased (P < 0.01) TVA (C18:1nt) from 5.6 to 9.0 ± 0.39 g/100 g of FA, linolelaidic acid (C18:2n-6t) from 0.2 to 0.4 g/100 g of FA, arachidic acid (C20:0) from 0.09 to 0.16 g/100 g of FA, and {gamma}-linoleic acid (C18:3n-6) due to increased intake of 18-C FA by steers fed YG. Level of YG linearly increased (P < 0.05) eicosenoic acid (C20:1n-9) from 0.20 to 0.26 ± 0.02 g/100 g of FA, and CLA (C18:2 cis-9, trans-11) from 0.23 to 0.34 ± 0.02 g/100 of FA. Increased TVA and CLA, which are intermediates in ruminal biohydrogenation of C18:2 and C18:3, probably resulted from incomplete ruminal biohydrogenation (Harfoot, 1981Go) and stearoyl-CoA ({Delta}9) desaturase enzyme in adipose tissue (Kim and Ntambi, 1999Go; Griinari et al., 2000Go). Additionally, beef from steers fed barley plus 6% tallow had less (P < 0.05) TVA (9.2 vs. 5.5 ± 0.55 g/100 g of FA), linoleic (4.5 vs. 3.2 ± 0.33 g/100 g of FA), linolelaidic (0.41 vs. 0.26 ± 0.20), arachidic (0.17 vs. 0.10 ± 0.01), and CLA (0.33 vs. 0.23 ± 0.03 g/100 g of FA) but more (P < 0.01) palmitoleic (3.2 vs. 3.8 ± 0.16 g/100 g of FA), heptadecenoic (1.15 vs. 1.34 ± 0.06), and oleic acids (33.7 vs. 37.1 ± 0.009/ 100 g of FA) than beef from steers fed corn plus 6% YG.


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  		Table 7. Fatty acid (FA) content (dry tissue basis) and composition of LM of steers fed corn plus yellow grease or barley plus tallow finishing diets
 
Two sources of CLA in beef are formed by biohydrogenation of linoleic acid by Butyrivibrio fibrosolvens (Kepler et al., 1966Go) and via desaturation of TVA in muscle, liver, or mammary gland (Griinari et al., 2000Go). Trans-vaccenic acid can be converted to CLA through {Delta}9-desaturation and can contribute 20 to 25% of the CLA in humans (Turpeinen et al., 2002Go; Kuhnt et al., 2006Go). Beef CLA content ranges from 2.0 to 5 mg/g of lipid in muscle (Mir et al., 2001Go, 2003Go; Gibb et al., 2004Go; Noci et al., 2005Go; Shah et al., 2006Go) and can be increased by feeding unsaturated vegetable oils (Beaulieu et al., 2002Go; Mir et al., 2002Go; Sackmann et al., 2003Go) or oil seeds (Madron et al., 2002Go; Gibb et al., 2004Go; Shah et al., 2006Go; Basarab et al., 2007Go) but not to levels suggested for optimum human health extrapolated from animal studies with synthetic CLA. However, substantially lower bioformed CLA appear to decrease cancer incidence (Knekt et al., 1996Go) and growth of human cancer cells in vitro (De La Torre et al., 2006Go). Extracted beef lipids decreased cancer cell growth more than synthetic CLA (De La Torre et al., 2006Go), and beef tallow increased potency of CLA in reducing mouse mammary tumor metastasis (Hubbard et al., 2006Go). Further, Hubbard et al. (2006)Go concluded that linoleic acid partially inhibited the ability of CLA to alter tumor viability but palmitic acid increased CLA potency.

Marks et al. (2004)Go increased beef CLA from 4.5 to 6.3 mg/g of total FA by feeding 6% YG in barley-based diets; 6% tallow increased beef CLA to 5.4 mg/g of total FA. In the current study, 6% YG increased beef CLA from 2.3 to 3.4 mg/g of total FA in corn-based diets, but beef from steers fed the barley plus 6% tallow diet was the same as control (2.3 mg of CLA/g of total FA). Trans-vaccenic acid increased linearly from 5.6 to 9.0 ± 3.9 mg/ g of total FA with increased YG, which was positively correlated with the increase in beef flavor. However, beef from steers fed corn plus 6% YG did not differ from that of steers fed barley plus 6% tallow for beef flavor but contained more (P < 0.05) TVA.

Altering the FA content of beef affects beef flavor (Ford et al., 1976Go). Beef flavor has been reported to be negatively correlated to stearic (Melton et al., 1982aGo,bGo) and linolenic (Melton et al., 1982aGo,bGo; Mandell et al., 1998Go) acids, but positively correlated to myristic (Larick and Turner, 1990Go), palmitic (Larick and Turner, 1990Go), palmitoleic (Melton et al., 1982aGo,bGo; Larick and Turner, 1990Go), and oleic (Larick and Turner, 1990Go; Mandell et al., 1998Go) acids. Of the FA that could have affected beef flavor, stearic, myristic, and palmitic acids were not affected by diet. However, beef from steers fed barley plus 6% tallow did not differ from steers fed corn plus 6% YG in beef flavor, but contained less (P < 0.01) TVA (5.5 vs. 9.2 ± 0.55 g/100 g of FA), so possibly the increased palmitoleic (3.8 vs. 3.2 ± 0.16/100 g of FA) and oleic (37.1 vs. 33.7 ± 0.06/100 g of FA) acids maintained beef flavor.

Therefore, feeding yellow grease increased diet energy content, which increased carcass fatness, and altered the muscle FA content, which increased beef fla-vor without affecting moisture retention, shelf life, or cooking properties of the beef. Additionally, beef from steers fed corn plus yellow grease was more tender and had greater PUFA content than beef from steers fed barley plus tallow.


   Footnotes
 
1 This work was supported by the Agricultural Research Center, College of Agricultural, Human, and Natural Resource Sciences, Washington State University, Pullman 99164 (Project No. 0304); Fats and Proteins Research Foundation, Inc., Bloomington, Indiana; Baker Commodities, Spokane, Washington, and ConAgra Foods, Lamb Weston, Richland, Washington. We thank D. C. Rule for verifying our fatty acid results. Back

2 Corresponding author: nelsonm{at}wsu.edu

Received for publication July 6, 2007. Accepted for publication January 4, 2008.


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


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