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Effects of supplemental fat on growth performance and quality of beef from steers fed barley-potato product finishing diets: II. Fatty acid composition of muscle and subcutaneous fat¹

Department of Animal Sciences, Washington State University, Pullman 99164-6351

	Abstract

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One hundred sixty-eight crossbred steers (317.1 ± 1.0 kg) were used to evaluate the effects of supplemental fat in finishing diets on the fatty acid composition, including the 9,11 isomer of conjugated linoleic acid, of beef. Steers were allotted within three weight blocks to a randomized complete block design with a 3 x 2 + 1 factorial arrangement of dietary treatments. Main effects were level of yellow restaurant grease (RG; 0, 3, and 6%), and level of alfalfa hay (AH; 3.5 and 7%) with an added treatment containing 6% tallow (T) and 7% AH in barley-based diets containing 15% potato by-product and 7% supplement (all dietary levels are on a DM basis) fed for an average of 165 d. Fatty acids of the LM and s.c. fat from four randomly selected steers per pen were quantified using GC after methylation with sodium methoxide. Dietary treatment did not (P > 0.10) affect total fatty acid (FA) content of the LM (143 ± 5.2 mg/g) or fat (958 ± 7.9 mg/g). Myristic acid increased linearly (P < 0.01) with increasing RG from 3.1 to 3.7 ± 0.1 g/100 g of FA in muscle. Stearic acid increased linearly (P < 0.05) as RG increased in the diet, from 11.4 to 12.9 ± 0.4 g/100 g of FA in LM and from 9.9 to 12.2 ± 0.3 g/100 g of FA in fat. Compared with T, steers fed 6% RG had more (P < 0.05) oleic acid in LM (42.7 vs. 40.3 ± 0.5 g/100g FA) and in fat (43.0 vs. 40.9 ± 0.5 g/100g FA). The cis-9, trans-11 conjugated linoleic acid (CLA) increased quadratically (P < 0.01) with increasing dietary RG in LM from 0.45 to 0.64 to 0.62 ± 0.03 g/100 g of FA and increased in fat from 0.61 to 0.84 to 0.83 ± 0.04 g/100 g of FA. Moreover, cis-9, trans-11 CLA was higher (P < 0.05) in fat from steers fed RG compared with T (0.81 vs. 0.69 ± 0.04 g/100 g of FA), and tended to be higher (P = 0.07) in muscle (0.62 vs. 0.54 ± 0.03 g/100 g of FA. Feeding yellow restaurant grease increased content of cis-9, trans-11 CLA in beef without an increase total FA content.

Key Words: Barley • Beef Cattle • Conjugated Linoleic Acid • Yellow Grease

	Introduction

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Fat content and fatty acid composition of beef have been studied extensively because of the relationship of fat to human health. Until recently, the focus has been on saturated fats and their effects on cholesterol and heart health. Recently, the fat composition of beef has been studied to explore the benefits of conjugated linoleic acid (CLA) isomers on human health, and to identify methods to increase the CLA content of beef. Several recent animal studies suggest that CLA may inhibit mammary and prostate cancer (Ip et al., 1999) and change body composition (Park et al., 1999). The two most abundant sources of CLA in the typical human diet are dairy products and meat from ruminants (Yurawecz et al., 1999; Ritzenthaler et al., 2001).

Recent studies indicate that feeding supplemental fats high in linoleic acid will increase the CLA content of meat (Mir et al., 2001). Most fat sources studied are in limited supply and too expensive to be cost effective for widespread use in the cattle feeding industry. Yellow grease may be an available, less expensive alternative fat source that contains substantial linoleic acid, unlike tallow, which does not contain substantial quantities of linoleic acid. Thus, the objective of this study was to evaluate the effects of supplemental yellow grease or tallow and level of alfalfa hay on the fatty acid composition of beef LM and s.c. fat from steers fed barley-based finishing diets.

	Materials and Methods

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Animals and Feeding

This experimental protocol was approved by the Washington State University Animal Care Committee (protocol No. 1601) and followed the Guide for the Care and Use of Agricultural Animals in Research and Teaching (FASS, 1999). One hundred sixty-eight cross-bred steers (317.1 ± 1.0 kg) were allotted within three weight blocks to a randomized complete block design with a 3 x 2 + 1 factorial arrangement of dietary treatments. There were 21 pens with eight steers per pen and three pens per treatment. The main effects (DM basis) were level of yellow restaurant grease (RG; 0, 3, or 6%) and level of alfalfa hay (AH; 3.5 or 7.0%), with an added treatment containing 6% tallow and 7% AH (T). All diets provided 417 IU of vitamin E/steer daily and contained 15% potato by-product and 7% supplement (DM basis), with the remainder as steamrolled Baronesse barley. Animals, diets, and feeding regimen, as well as the effects of diet on growth performance and energy intake, were described in detail by Nelson et al. (2004). Steers in the heavy block were fed for 146 d, whereas the medium and light blocks were fed for 175 d (average of 165 d on feed). Steers were weighed at the Washington State University Cattle Laboratory in Pullman, and then transported 320 km to a commercial plant where they were humanely slaughtered on the day of shipping.

Longissimus Muscle Sampling

After chilling for 24 h at –1 to 0°C, boneless strip loins were removed from the left side of four randomly selected carcasses per pen (84 total). In all pens, growth and carcass characteristics did not differ (P > 0.10) between the sampled steers and the entire pen (results not shown). 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 and transported in coolers on ice to the Washington State University Meat Laboratory. After 14 d of postmortem aging at 2°C, one 4 x 4 cm adipose tissue sample, including the entire s.c. fat profile, was removed from over the anterior end of the LM. All remaining s.c. fat was then removed from the strip loin, and one 1.3-cm LM slice was removed from the anterior end. 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, 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 fatty acid analysis.

Chemical Analyses

Crude protein and ether extract contents of muscle samples were determined by AOAC (1990) methods. These analyses were run in duplicate, and results were reported on a DM basis.

Fatty Acid Analyses

Lipid from duplicate 100-mg LM samples, and 50-mg s.c. fat samples, were extracted in 3 mL of chloroform-methanol (Folch et al., 1957) containing C19:0 as an internal standard, and clarified using chloroform, distilled water, and 33% KCl solution. Lipids were methylated with sodium methoxide (MeOH/NaOH₃) for 4 h in a 55°C water bath. This procedure methylates esterified fatty acids (FA) but not FFA (Kramer et al., 1997), and does not form CLA artifacts, as sometimes occurs with other methylating procedures. Methylated FA were extracted in hexane and quantified by GC using a 60 m x 0.25 mm x 0.50 µm column (model CP8748; Varian, Walnut Creek, CA) in a GC (model 5890, Hewlett-Packard, Avondale, PA) with 2.81 kg/cm² head pressure (He, 1 mL/min), and 2 µL injection volume. Injector and flame ionization detector temperatures were set at 260°C. Initial oven temperature was 60°C for 2 min, increased to 200°C at 10°C/min, increased to 240°C at 2°C/min, held at 240°C for 23 min, and then increased to 250°C at 50°C/min and held there for 30 min.

Statistical Analyses

Data were analyzed as a randomized complete block design, with a 3 x 2 + l factorial arrangement of dietary treatments using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Pen served as the experimental unit. The main effects were level of RG (0, 3, or 6%), and level of AH (3.5 or 7.0%), with an added treatment of 6% T. Least squares means were separated by preplanned contrasts for RG level, AH level, RG x AH, and 6% RG with 7% AH vs. 6% T with 7% AH (Steel and Torrie, 1980). Simple (Pearson) correlations were calculated between some carcass measurements and some LM measurements using the CORR procedure of SAS.

	Results and Discussion

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Subclass least squares means for all dependent variables are presented in Tables 1 and 2. When interactions were not significant (P > 0.10), main-effect least squares means and SE are reported in the text.

The DM and ether-extractable fat (EE) content of the LM increased linearly (P < 0.01) with level of RG from 27.2 to 28.1 ± 0.18% and 13.1 to 16.1 ± 0.01, respectively. The CP content decreased linearly (P < 0.05) as dietary RG level increased, from 80.5 to 77.9 ± 0.76% (Table 1). Total FA content was not (P > 0.10) affected by diet, but, as expected, treatment means for total FA tended to correspond closely with means for EE (r = 0.74; P < 0.01). Moreover, treatment means for EE and marbling scores (Nelson et al., 2004) varied in the same direction (r = 0.49; P < 0.05). Increased DM, EE, and total FA were generally associated with decreased CP (r = –0.84, –0.97, and –0.74, respectively; P < 0.01), because, as fat deposition occurred, it diluted the protein and the water associated with the protein.

Fatty acid composition of LM, in general, was similar in steers fed barley-potato product finishing diets, as reported by Nelson et al. (2000) and Rule et al. (2002), except that greater CLA and lower stearic acid (C18:0) was found in the current study. However, specific FA were also altered by diet. Myristic acid (C14:0) increased linearly (P < 0.01) with level of RG in the diet from 3.16 to 3.67 ± 0.18 g/100 g of FA (Table 1). This increase could be due to the increased amount of total C14:0 contained in the fat-supplemented diets (Nelson et al., 2004). The cis-10-pentadecenoic acid (C15:1) levels in LM were lower (P < 0.01) for steers fed RG compared with T (0.05 vs. 0.13 ± 0.01 g/100 g of FA), and decreased quadratically (P = 0.05) with level of RG from 0.09 to 0.05 ± 0.01 g/100 g of FA. For palmitoleic acid (C16:1) there was a quadratic RG x AH interaction (P < 0.05), where C16:1 was maximized with 0% RG for 3.5% AH diets and with 3% RG for 7% AH diets. Compared with the T treatment, steers fed RG had less (P < 0.01) heptadecanoic acid (C17:0) and cis-10-heptade-cenoic acid (C17:1). Moreover, C17:1 decreased linearly (P < 0.01) as RG level increased in the diet. The smaller amounts of C15:1, C17:0, and C17:1 in LM of steers fed RG than T may be because the T diet contained more odd-chain length fatty acids (Nelson et al., 2004). The decrease in odd-chain length FA associated with increasing RG may have been associated the increased number of even-chain carbon skeletons provided by the RG, or with alterations in ruminal fermentation thereby decreasing synthesis of odd-chain FA from propionate; however, the exact mechanism needs to be determined. Stearic acid (C18:0) increased linearly (P < 0.01) with level of RG from 11.43 to 12.90 ± 0.38 g/100 g of FA. This increase may be due to the increased 18-C skeletons supplied by the RG supplemented diets for ruminal biohydrogenation. Oleic acid (C18:1) was higher (P < 0.01) for steers fed RG than for those fed T (42.72 vs. 40.27 ± 0.48 g/100g FA), and cis-9, trans-11-conjugated linoleic acid (CLA9,11) increased quadratically (P < 0.01) with level of RG from 0.45 to 0.64 to 0.62 ± 0.03 g/100g FA. There was also a tendency (P = 0.07) for LM from steers fed RG to have more CLA9,11 than LM from steers fed T. Increased C18:1 and CLA9,11 (intermediates of ruminal biohydrogenation of C18:2 and C18:3) associated with RG probably resulted, at least in part, from the high level of unsaturated 18C fatty acids in the RG diets (Nelson et al., 2004); however, an effect of RG on stearoyl-CoA (-9) desaturase enzyme activity (Kim and Ntambi, 1999; Griinari et al., 2000) in adipose tissue cells cannot be ruled out. The exact mechanism for the increase in C18:1 and CLA9,11 caused by RG needs to be elucidated. Behenic acid (C22:0) and erucic acid (C22:1) decreased linearly (P < 0.01) as RG level increased in the diet. There were no effects (P > 0.10) of diet on myristoleic (C14:1), pentadecanoic (C15:0), linoleic (C18:2), linolenic (C18:3), trans-10, cis-12-conjugated linoleic (CLA10,12), or arachidic acid (C20:0) in LM.

Dry Matter and Fatty Acid Analyses of Subcutaneous Fat

Subcutaneous fat DM decreased linearly (P < 0.01) as RG level increased in the diet, and samples from steers fed RG had less (P < 0.01) DM than steers fed T (Table 2). In contrast to muscle, DM and total FA contents were not related.

With few exceptions, the effect of diet on the FA composition of fat was similar to the effect in the LM. As in the LM, total FA content was not affected (P > 0.05), and there was a linear increase (P < 0.01) in C14:0 with increasing level of RG in the diet. Moreover, odd-chain FA either decreased (P < 0.05) or tended to decrease (P = 0.06) as dietary RG increased, and fat from steers fed RG had fewer (P < 0.05) odd-chain FA than those fed T. This was probably due to the increased odd-chain-length FA provided by T compared with RG (Nelson et al., 2004). Stearic acid increased linearly, and CLA9,11 quadratically, with level of RG (P < 0.01). Additionally, C18:1 (P < 0.01) and CLA9,11 (P < 0.05) were higher in fat from steers fed RG compared with T. Fat from steers fed RG had less (P < 0.01) C16:1 than steers fed T, and there was a quadratic RG x AH interaction (P < 0.05) caused by a faster rate of decline due to RG in 7% AH than 3.5% AH diets. Linoleic acid in s.c. fat decreased linearly (P < 0.01) with increasing levels of RG from 2.02 to 1.51 ± 0.12 g/100 g of FA, and decreased (P < 0.05) with level of AH from 1.92 to 1.62 ± 0.72 g/100 g of FA. Arachidic acid increased, and C22:0 decreased, linearly with level of RG (P < 0.01), but diet did not affect (P > 0.10) C14:1, C18:3, or C22:1 in s.c. fat.

There are reports of altered beef muscle or adipose FA composition due to manipulation of ruminal fermentation or protection of unsaturated fatty acids from ruminal biohydrogenation (Harfoot, 1981). Saturated FA, notably myristic (C14:0) and palmitic (C16:0), are hypercholesterolemic and thrombogenic (Scientific Review Committee, 1990; Simopoulos, 1991). In the current study, RG linearly increased (P < 0.01) C14:0, but the total increase in C14:0 and C16:0 was only a total of 0.6 g/100 g of FA, which was not statistically significant or nutritionally relevant. If 100 g of fresh weight of beef steak containing as much as 8% fat were consumed, it would increase intake of these two hypercholesteremic FA by less than 0.05 g.

Monounsaturated FA have been considered neutral on human blood cholesterol (Scientific Review Committee, 1990), but Mattson and Grundy (1985) reported that dietary oleic acid (C18:1) was associated with decreased plasma low density lipoprotein cholesterol. Due to de novo FA synthesis and synthesis from stearic acid by the stearoyl-CoA (-9), desaturase enzyme in adipose tissue, oleic acid is the most abundant FA in beef tissue (Rule et al., 1994). Beef from steers fed RG contained 2.5 g/100 g of FA more C18:1 than those fed T in the current study.

Polyunsaturated FA are hypocholesterolemic (Scientific Review Committee, 1990), and are required for human growth, development, reproduction, and health (Neuringer et al., 1988). In the current study, linoleic and linolenic acid content of beef was not affected by diet. Additionally, CLA (C18:2cis-9,trans-11) has potent chemopreventive effects on cancerous tumors (Ha et al., 1990; Ip, 1997). Mir et al. (2000) and Laborde et al. (2001) found no beef cattle breed differences in CLA in lipid profiles of muscle tissue, but diet could impact the CLA content of beef (Enser et al., 1999). Conjugated linoleic acid is an intermediate in the ruminal biohydrogenation pathway (Viviani, 1970; Harfoot, 1981); therefore, increasing the rate of ruminal outflow or slowing biohydrogenation will increase ruminal outflow of CLA. Additionally, greater quantities of CLA may result from the -9 desaturase system (Kim and Ntambi, 1999) in adipose tissue from transvaccenic acid (C18:1trans-11). Therefore, dietary modification, such as fat addition, is probably the most likely means to improve FA composition for human health.

Laborde et al. (2001) found 19 mg of CLA/100 g of fresh beef, whereas 17 mg of CLA/100 g of fresh beef was found in the current study. Beef from the current study, however, was leaner (3.5 vs. 5.7 g of EE/100 g of fresh weight) and had a greater proportion of CLA in the total lipid (0.45 vs. 0.36 g of CLA/100 g of FA) than did the beef of Laborde et al. (2001). Additionally, CLA in the total lipid was increased from 0.45 to 0.63 g of CLA/100 g of FA by feeding RG.

To obtain chemopreventive effects, Decker (1995) suggested that a 70-kg human should consume at least 1.5 g of CLA/d. If one assumes consumption of 100 g of fresh weight/d of beef (Enser et al., 1996) and no cooking loss, beef from steers fed RG would provide 26 mg of CLA, but steers fed no RG would supply only 17 mg of CLA. This is only 1 to 2% of the suggested CLA intake; however, enhancing the CLA content of commonly consumed higher fat foods such as ground beef and sausages could have nutritional relevance.

	Implications

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Results from this study confirm that feeding supplemental fats can alter the fatty acid profile of beef. Yellow restaurant grease may be a source of fat that will result in beef, which as a part of a balanced diet, could contribute to increasing total conjugated linoleic acid intake of humans without increasing total fat intake.

	Footnotes

 
¹ This work was supported by the Agric. Res. Center, College of Agric. and Home Econ., Washington State Univ., Pullman 99164 (Projects 0304 and 0432); the Fats and Proteins Research Foundation, Inc., Bloomington, IN; and the Washington Cattle Feeders Association, Pasco, WA.

² Current address: Univ. of Wyoming Cooperative Ext. Service, Box 1708, Jackson 83001-1708.

³ 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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