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ANIMAL PRODUCTION |
* Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Northern Crops Institute, Fargo, ND 58105;
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Carrington Research Extension Center, Carrington, ND 58421
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Animal and Range Sciences Department, South Dakota State University, Brookings 57007
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# Department of Pharmacology, Physiology, and Therapeutics, School of Medicine and Health Sciences, University of North Dakota, Grand Forks 58203
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: beef cattle • fatty acid • finishing • flax • processing • sensory characteristic
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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) and is very energy dense (2.82 Mcal/kg of NEm, 1.96 Mcal/kg of NEg; Lardy and Anderson, 2003). The oil fraction of flax is approximately 50% 
-linolenic (18:3n-3) acid (ALA; Daun and Przybylski, 2000), an omega-3 fatty acid that stimulates human immune function and reduces the risk of cardiovascular disease (Connor, 2000).
Feeding flax at 5% of diet DM in beef feedlot diets has resulted in increased DMI (Drouillard et al., 2004) and percentage of carcasses grading USDA Choice or greater (Drouillard et al., 2002, 2004). Additionally, Drouillard et al. (2004) compared cooked ribeye steaks from steers fed flax or tallow and noted increases in n-3 fatty acids in steaks from steers fed flax. Including fat (tallow or oilseeds) in finishing diets has increased gain efficiency (Bartle et al., 1994) and improved ADG (Brandt and Anderson, 1990; Krehbiel et al., 1995) but generally has not affected carcass composition (Bartle et al., 1994; Krehbiel et al., 1995). However, Felton and Kerley (2004a) reported greater marbling scores in steers fed whole soybeans or choice white grease when compared with diets with no additional fat.
Gibb et al. (2004) compared whole with rolled sun-flower seeds in feedlot diets and noted that processing increased DMI, but no differences in performance or carcass traits were observed. Pires et al. (1997) found that grinding cottonseed increased total tract OM and N digestibility in dairy cows but did not affect milk production. Therefore, objectives of this study were to determine the effect of 8% flax addition to beef feedlot diets on performance, carcass composition, and muscle fatty acid profiles, and determine effects of flax processing on the same variables.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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. Heifers were implanted with 20 mg of estradiol benzoate and 200 mg of testosterone propionate (Fort Dodge Animal Health, Overland Park, KS) at the beginning of the study and were not reimplanted. Heifers were offered a growth diet (Table 1) for the first 56 d, after which they were adapted to a finishing diet. The control diet used linseed meal, a by-product of flax oil extraction, as a protein source to more clearly evaluate the effect of the flax oil.
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). Heifers were weighed every 28 d during the study. Final live BW were estimated by dividing HCW by 0.62 (i.e., a 62% dressing percent).
Slaughter, Data Collection, and Sampling Procedures
Once heifers within a block were visually appraised to have approximately 1 cm of subcutaneous fat over the 12th rib, they were transported to Tyson Fresh Meats in Dakota City, NE (approximately 750 km) and slaughtered, and HCW were collected. Two blocks were slaughtered after 96 and 97 d on feed, and 2 blocks were slaughtered after 124 d on feed. After a 24-h chilling period, carcasses were ribbed between the 12th and 13th ribs, and fat thickness and LM area were measured, and marbling score, KPH, and USDA quality grade were recorded by trained North Dakota State University personnel.
Longissimus muscle sections, caudal to the 12th rib and approximately 6 to 8 cm thick, were removed from the left side of each carcass, tagged to preserve individual animal identity, and immediately transported in coolers (<4°C) to the meats laboratory at North Dakota State University where they were trimmed, vacuum-packaged, and aged at 4°C for 14 d. After the aging period, LM sections were cut into two 2.54-cm-thick steaks, and a 100-g sample of LM was removed for i.m. fatty acid analysis. Steaks were frozen at –20°C until they were evaluated for Warner-Bratzler shear force determination and trained sensory panel evaluations of palatability traits, whereas LM samples were stored frozen (–20°C) for subsequent fatty acid determination.
Fatty Acid Profiles
Frozen muscle samples were pulverized under liquid nitrogen. Lipids from the tissue powder were extracted using a single-phase extraction with n-hexane/2-propanol (3:2 vol/vol; Hara and Radin, 1978). After centrifugation at 800 x g to pellet debris, the lipid-containing liquid phase was decanted and stored at –80°C until analysis.
Phospholipids and neutral lipids were separated by liquid column chromatography, using activated silicic acid (Clarkson Chemical Company Inc., South Williamsport, PA) as the stationary phase. Neutral lipids, containing cholesterol, triacyl- and diacylglycerols, were eluted with 10 vol of chloroform:methanol (58:1 vol/vol; Murphy and Schroeder, 1997). Phospholipids were eluted with 10 vol of methanol. The eluents were stored at –80°C until analysis. Phospholipids and neutral lipids were subjected to base-catalyzed transesterification, converting the acyl chains to fatty acid methyl esters. To each fraction, 2 mL of 0.5 M KOH dissolved in anhydrous methanol was added (Brockerhoff, 1975). Fatty acid methyl esters were extracted from the methanol using 2 mL of n-hexane, and the n-hexane phase containing the fatty acid methyl esters was removed. The lower phase was reextracted 2 more times with n-hexane, and these washes were combined with the original aliquot.
Individual fatty acids were separated with a Trace GLC (ThermoElectron, Austin, TX) using an SP-2330 column (0.32 mm i.d. x 30 m length; Supelco, Bellfonte, PA) equipped with autosamplers and dual flame ionization detectors. Injector and detector temperatures were 220°C; He was the carrier gas, with a 25:1 split. The initial column temperature was 150°C, and the temperature was held for 5 min, after which it was increased at 2.5°C per min until 220°C was reached. The makeup gas was nitrogen. Fatty acids were quantified using a standard curve from commercially purchased standards (NuChek Prep, Elysian, MN), and 17:0 was the internal standard (Murphy et al., 2004).
Palatability Attributes
Sensory panel evaluations were performed according to AMSA (1995) guidelines. Steaks were thawed and then cooked on a Farberware Open Hearth broiler (Farberware Company, Bronx, NY) to an internal temperature of 35°C, flipped, and cooked to a final internal temperature of 71°C. An 8-member trained panel evaluated each cooked steak for tenderness, juiciness, and flavor using an 8-point scale (8 = extremely tender, extremely juicy, extremely flavorful to 1 = extremely tough, extremely dry, extremely bland).
Warner-Bratzler shear force values were determined according to AMSA (1995) guidelines. Steaks were prepared in the same manner as for sensory panel evaluations. After allowing the steaks to cool to room temperature (approximately 23°C), at least six 1.3-cm-diam. cores were removed from each steak parallel to the muscle fiber orientation, and each core was sheared once through the center using a Warner-Bratzler shear device (G-R Electrical Manufacturing Co., Manhattan, KS). The mean Warner-Bratzler shear force value for each steak was the average of a minimum of 6 cores.
Dietary Energy
The finishing phase of the study was used to determine differences in NEm and NEg between whole, rolled, and ground flax. Metabolizable energy values were determined by the methods described previously by Hays et al. (1987). Briefly, animal requirements for NEm and NEg were determined from the NRC (1984) equations for medium-framed heifers. Using the quadratic relationship between NEm and NEg described in Hays et al. (1987), dietary NEm was calculated and converted into diet TDN and subsequently dietary ME by NRC (1996) equations. The ME contributed by all other feed-stuffs in the diet, as determined by using NRC (1996) values, was subtracted, leaving the dietary ME contribution of flax. Subsequent NEm and NEg values were calculated according to NRC (1996) equations.
Statistical Design and Analysis
Data were analyzed as a randomized complete block design using the Mixed model procedure of SAS (SAS Inst. Inc., Cary, NC). Pen served as the experimental unit (n = 4) for all dependent variables. Block was considered a random effect for all statistical analyses. Treatment was the fixed effect in the model for performance and carcass data, including Warner-Bratzler shear force. Trained sensory panel data were analyzed with treatment as the main effect and treatment, marbling score, and panelist as covariates. The Univariate procedure of SAS was used to ensure normality of reported quality grade percentages. Preplanned contrasts were used to compare control to flax diets (WHL, RLD, and GRD), WHL to processed diets (RLD and GRD), and RLD to GRD. Contrasts were protected by a treatment P value of 0.05.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Most studies have reported that increasing fat percentage in the diet results in lower DMI (Bartle et al., 1994; Ramirez and Zinn, 2000; Felton and Kerley, 2004a); however, Drouillard et al. (2004) reported that feeding ground flax at 5% of diet DM increased intake across several studies (receiving steers and heifers, finishing beef steers, and finishing Holstein steers). Additionally, Gibb et al. (2004) noted an increase in DMI when feeding sunflower seeds at 9 and 14% of diet DM but attributed this to additional NDF found in the fibrous hull of the sunflower, which agrees with Zinn and Plascencia (1996), who also reported DMI increased with increasing lipid supplementation if fiber levels were also increased. The reason flax did not affect DMI in this study is unclear. It is possible that fiber from the hull (20% NDF, DM basis; Canadian Grain Commission, 2001) might offset any oil effects in regard to reduced intake.
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). Drouillard et al. (2004) found no difference in ADG or G:F of corn-based diets between control diets and diets containing 5% ground flax fed to finishing heifers. Several studies have reported that supplemental fat has increased G:F due to decreases in DMI (Bartle et al., 1994; Krehbiel et al., 1995; Andrae et al., 2001); however, Felton and Kerley (2004b) noted no change in DMI, ADG, or G:F when feeding increasing levels of whole raw soybeans to finishing steers. In our study, we report increases in G:F despite no difference in DMI, so the improvement in gain may have resulted from the increased energy density of the flax diets. Results from our study indicate that more nutrients were available because of processing, resulting in improved performance. Differences were noted between WHL and processed (RLD and GRD) flax for calculated NEm (P = 0.003) and NEg (P = 0.003) values (Table 2), suggesting that reducing particle size or breaking the seed coat increases the benefits of flax inclusion. These differences in performance may in part be attributed to increased degradable intake protein availability found in the processed flax diets. Corn-based finishing diets, although adequate for metabolizable protein, can be deficient in degradable intake protein (Shain et al., 1998). The diets in this study contained NPN in the form of urea (0.11 to 0.15%), but these levels might have been inadequate for maximal rumen function (Cooper et al., 2002). Gibb et al. (2004) reported that processing sunflower seeds did not increase available energy. This may be due to differences in the seed hull. Sunflower seeds are 39% ADF (Bath et al., 1993), and when fed, may reduce passage rate and negate any differences in nutrient availability processing may create. Limited literature is available concerning processing of oilseeds, but Gibb et al. (2004) compared whole or rolled sunflower in feedlot diets fed at either 9 or 14% of diet DM and found no performance differences as a result of processing.
Carcass Data
Hot carcass weights were greater (P < 0.001) in heifers fed flax diets, and processing flax also increased (P = 0.009) carcass weights compared with feeding flax whole (Table 3). No treatment differences were noted for fat thickness over the12th rib (P = 0.32), LM area (P = 0.23), or KPH fat (P = 0.07). Flax addition increased USDA yield grade (P = 0.01). Treatment did not affect (P = 0.14) marbling score. Including lipid sources in finishing diets has generally not affected carcass composition (Bartle et al., 1994; Felton and Kerley, 2004a). However, Drouillard et al. (2004) reported that feeding flax produced conflicting results with respect to USDA yield grade when compared with control diets. Those researchers noted that feeding greater levels (15% DM) of flax to feedlot steers reduced USDA yield grade when compared with steers fed 5% (DM) flax. In a companion study, Drouillard et al. (2004) reported no differences in USDA yield grade between heifers fed 0 or 5% (DM) flax. The reasons that these results differ between studies are not immediately clear.
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also reported that flax increased the percentage of carcasses that graded USDA Choice. Furthermore, Andrae et al. (2001) noted that feeding high oil corn increased marbling score. Garrett et al. (1976) reported that carcass quality grades increased when feeding rumen protected fat sources. Results from this study are similar to those of Zinn (1989), who fed either yellow grease or blended animal and vegetable fat at different levels and reported that increasing dietary fat percentage linearly increased KPH fat and marbling scores but decreased carcass yield.
Shear Force and Palatability Attributes
Treatment did not affect sensory panel tenderness ratings (P = 0.44), flavor ratings (P = 0.35), or Warner-Bratzler shear force (P = 0.06; Table 4). Steaks from the control group rated juicier than those from flax treatments (P = 0.05). Maddock et al. (2003) reported that steaks from flax-fed steers were less juicy and more tender than steaks from steers finished on a corn-based control diet that did not contain flax. However, it is difficult to explain the biological basis why steaks from heifers fed RLD would be considered juicier than steaks from GRD or WHL. Drouillard et al. (2004) noted no differences in sensory traits or shear force for steers and heifers fed differing levels of flax or in Holstein steers fed 5% flax. Additionally, most literature suggests including fat in beef finishing diets has typically not affected sensory panel response (Brandt et al., 1992; Andrae et al., 2001; Gilbert et al., 2003).
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) and those incorporated into neutral lipids (triglycerides, diglycerides, and cholesteryl esters; Table 6). Only those fatty acids 16C and longer were measured, and fatty acid concentration is expressed as grams per 100 g of total identified fatty acids.
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). Fewer differences were observed for neutral lipids. Alpha-linolenic acid was increased by flax addition (P < 0.001) and processing (P < 0.001), but less neutral lipid ALA was noted in heifers fed GRD compared with RLD (P = 0.04). However, the biological significance of this finding is questionable because the differences were relatively small (0.58 vs. 0.52 g/100 g, respectively). The addition of flax also increased neutral lipid linoleic acid (P = 0.004) and arachidonic acid (P = 0.03), and processing increased neutral lipid levels of arachidonic acid (P = 0.007). The increase in arachidonic acid is likely the result of increased proportions of linoleic acid, but why there was an increase in linoleic acid in the neutral lipid and not the phospholipid is unclear.
Previous work with supplemental fat sources in ruminants has produced mixed results relative to changing muscle fatty acid profiles. Elmore et al. (2000) fed flax, fish meal, or both to 2 breeds of sheep and noted similar increases to this study for muscle ALA content, but they did not report increases in EPA, DPA, or DHA in flax-fed lambs. Similar to these results, Elmore et al. (2000) also noted a decrease in arachidonic acid in flax-fed lambs when compared with lambs not fed flax. Similarly, Raes et al. (2004) offered either crushed or extruded flax to Belgian Blue bulls and reported muscle ALA (g/100 g of total fatty acids) was increased, but longer chain n-3 fatty acids were not, and DHA was lower in flax-fed bulls. Raes et al. (2004) reported decreased muscle n-6 fatty acids in flax-fed bulls, which are consistent with the findings in our study.
These results suggest that at least a portion of dietary ALA from flax escapes rumen biohydrogenation and is subsequently unsaturated and elongated into longer chain polyunsaturated n-3 fatty acids for incorporation into phospholipids. However it appears that long-chain polyunsaturated fatty acids biosynthesized from flax oil are not easily incorporated into triglycerides. These findings agree with those reported by Wood et al. (1999), who reported EPA and DHA are more readily incorporated into phospholipids than triglycerides. Additionally, Ashes et al. (1992) noted that ruminants have difficulty incorporating C20 and C22 fatty acids into triglycerides. Choi et al. (2000) and Raes et al. (2004) reported competitive inhibition of the elongation and desaturation of linoleic acid when high amounts of ALA are found in the diet. Jump (2002) also reported competition between EPA and arachidonic acid for incorporation into cell membranes, which may help explain the decrease in arachidonic acid in the phospholipid fraction.
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IMPLICATIONS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 Corresponding author: glardy{at}ndsuext.nodak.edu
Received for publication September 2, 2005. Accepted for publication January 18, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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