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Influence of fish oil in finishing diets on growth performance, carcass characteristics, and sensory evaluation of cattle¹

Department of Animal Science, University of Arkansas, Fayetteville 72701

	Abstract

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

 
Inclusion of fish oil, a source of n-3 fatty acids, in ruminant diets may fortify the fatty acid composition of meats and alter consumer perceptions of taste. Therefore, a 70-d study of 16 crossbred steers (441 ± 31.7 kg of initial BW; 4 steers/pen; 2 pens/dietary treatment) consuming a high concentrate diet was conducted. Dietary treatments consisted of 1) control (75% corn, 11% soybean meal, and 10% cottonseed hull-based diet) and 2) the control diet with 3% fish oil replacing a portion of the corn. Steers were weighed on consecutive days at d 0 and 70 (i.e., the beginning and end of the trial), and interim weights were taken on d 28 and 56. On d 63, all steers were bled by jugular venipuncture to determine plasma fatty acid profiles. Steers were stratified by treatment and slaughtered on d 71 and 72. Fish oil supplementation decreased ADFI (13.97 vs. 11.49 kg; P < 0.01); however, it had no effect on ADG (P = 0.20) or G:F (P = 0.27). Fish oil supplementation increased (P < 0.01) the concentrations of MUFA, as well as linolenic and eicosapentaenoic acid in the plasma. Fish oil supplementation did not alter (P > 0.24) the color of the LM, LM area, yield grade, dressing percent, marbling, quality grade, or fat thickness. However, after extended (15 mo) storage at – 20° C, a professional descriptor panel discerned steaks from steers that had been supplemented with fish oil from a commercially available product or steaks from control steers. In summary, supplementation with fish oil decreased feed intake and subsequent HCW (P = 0.06) and had varying effects on sensory traits. Nevertheless, fish oil supplementation increased the proportions of n-3 fatty acids in the plasma, which may increase acceptability of the meat to the beef consumer.

Key Words: cattle • fatty acid • fish oil • n-3 fatty acid • professional descriptive panel

	INTRODUCTION

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

 
Ruminants have the ability to utilize by-products from numerous industries as nutrients. Fish industry by-products are potential sources of valuable nutrients, including energy and protein. Fish oil is currently not widely utilized by the beef cattle industry because there are cheaper fat sources. Typically fat is limited to < 5% in cattle diets to minimize negative effects on ruminal fiber digestion. In the rumen, most triglycerides are broken down and the fatty acids are hydrogenated; however, research indicates that increasing the proportion of n-3 fatty acids in ruminant diets may modify the fatty acid composition of meat (Wistuba et al., 2003) and milk (Ashes et al., 1992).

The future is likely to bring considerable emphasis on the modification of fatty acid composition of beef. Recently, the dietary recommendation for humans of the very long chain highly unsaturated fatty acids, specifically the n-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid, has increased from 0.15 to 0.65 g/d (Kris-Etherton et al., 2000). Increased consumption of these polyunsaturated n-3 fatty acids is linked to beneficial changes in cardiovascular health (Schmidt et al., 2001), eicosanoid biosynthesis, and gene expression (Shahidi and Miraliakbari, 2004). Therefore, the objective of this study was to determine the effects of dietary Menhaden fish oil addition on carcass and sensory characteristics and growth performance of cattle consuming a high concentrate diet.

	MATERIALS AND METHODS

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

 
Animals and Feed

All animal care and sample collection procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee. Sixteen Angus crossbred steers (441 ± 31.7 kg of initial BW) from the same maternal herd were obtained from the University of Arkansas Stocker and Receiving Unit in Savoy. Steers were blocked by weight and randomly assigned to 3.7 x 29.3-m pens with covered bunks and bunk aprons, such that 4 steers were maintained in each of 4 pens, for a total of 8 steers/dietary treatment. Dietary treatments (Table 1) consisted of 1) a control diet and 2) the control diet with 3% fish oil replacing corn on an equal weight basis. Diets were mixed at approximately weekly intervals. Steers were allowed ad libitum access to their respective diets and water for 70 d beginning on October 24, 2000. Steers were weighed on consecutive days at the beginning (d 0) and conclusion (d 70) of the trial, and interim weights were taken on d 28 and 56. Feed samples were collected on weigh days and analyzed to quantify DM, CP (procedure 990.03; AOAC, 1990), and crude fat (procedure 920.39C; AOAC, 1990). Concentrations of NDF and ADF in feed samples were determined nonsequentially by batch procedures outlined by Ankom Technology Corp. (Fairport, NY).

All steers were bled by jugular venipuncture on d 63. Blood was collected into two 10-mL vacuum tubes containing sodium heparin (Vacutainer 366480, Becton Dickinson, Franklin Lakes, NJ) to determine plasma fatty acid concentrations. Plasma fatty acids were determined by the methods outlined by Sasser (1993). Briefly, plasma samples were freeze-dried, and 50 mg was subjected to direct saponification in 2.0 mL of a 1:1 (vol/vol) methanol/distilled water solution containing 3.26 M NaOH in tubes that were securely sealed and heated for 5 min in a 90° C water bath. Tubes were removed from the water bath and vigorously vortexed for 5 s. Tubes were then returned to the 90° C water bath for an additional 25 min, removed, and cooled quickly by plunging into cool tap water (approximately 15.6° C). Samples were methylated by adding 4.0 mL of a 0.85:1 (vol/vol) methanol/6.0 N HCl solution, recapped, heated for 10 min at 80° C, and rapidly cooled by plunging into cool tap water. Fatty acids were extracted by the addition of 2.5 mL of a 1:1 (vol/vol) HPLC-grade hexane/methyl tert-butyl ether solution [containing an internal standard (methyl 13:0, 0.5 mg/mL)] and gentle tumbling on a clinical rotator for 10 min. The aqueous phase was discarded, and 1.5 mL of a 0.3 M NaOH solution was added to the organic phase remaining in the tube. Tubes were recapped and tumbled again for at least 5 min, and approximately 2/3 of the organic phase was pipetted into a GC vial and capped. Fatty acids were determined by GC using a 25 m x 0.2-mm fused silica capillary column (HP 5890 series II; Hewlett Packard, Newark, DE) with a split ratio of 50:1 and hydrogen as the carrier gas for a column flow rate of 1.0 mL/min. Injector and detector temperatures were 300° C, and column temperature was ramped from 170 to 300° C at 5° C/min. Identification of peaks was accomplished using purified standards (Nu-Chek Prep, Elysian, MN; Matreya, Pleasant Gap, PA).

Animal Slaughter and Tissue Collection

Cattle were stratified by treatment, and 2 steers/pen were slaughtered on d 71 and 72. Steers were stunned via captive bolt gun and exsanguinated by severing the jugular veins on both the right and left sides. Hot carcass weights were obtained on the day of slaughter, whereas 12th-rib fat thickness, LM area, percentage of KPH, marbling scores, and skeletal maturity scores (USDA, 1997) were collected by a trained, experienced evaluator after carcasses had been chilled at 2° C for 24 h. The area of the LM was traced onto acetate paper (Bee Paper Co. Inc., Wayne, NJ), and grid measurements were made of the tracing. At 96 h postmortem, the left primal ribs from each carcass were removed and subsequently cut into 3 sections including the sixth to seventh, eighth to ninth, and 10th to 12th ribs. The interface between the 12th and 13th ribs was used to obtain the following carcass measurements before removal: 1) subcutaneous fat (mm) at , , and of the length (dorsal to ventral direction) of the LM; 2) intramuscular fat (marbling); and 3) LM area (LMA, cm²).

To quantify DM, CP (990.03), lipid (920.39C), and ash (923.03) concentrations, the LM from the 10th to 12th ribs was removed and stripped of surrounding epimysium, ground, and freeze-dried for analysis using the procedures of the AOAC (1990). The sixth to ninth rib sections were then vacuum-packaged (ca 125 torr) in barrier bags (B-620 barrier bag; 30 to 50 mL O₂/m²/24 h/760 torr/23° C; Cryovac, Duncan SC), and aged until 14 d postmortem at 2 to 4° C. After the aging period, the eighth to ninth rib section was cut into 2.54-cm-thick steaks, individually packaged in butcher paper, and stored at – 20° C for 15 mo until the professional descriptor panel analysis for aromatic and palatability characteristics.

Color Data Determination. Color data were collected on ribbed carcasses 48 h postmortem. Objective color of the LM was measured with a Hunter MiniScan XE (model 45/0-L, Hunter Associates Laboratory, Inc., Reston, VA) after a 45-min bloom period at 2° C. Objective color (L*, a*, and b* values; CIE, 1976) was determined from the mean of 3 random readings on the LM using illuminant C and a 10° standard observer. The spectrocolorimeter had a 22-mm aperture and was calibrated against a standard white tile (No. M04207 with X = 81.1, Y = 85.9, and Z = 91.6; Hunter Associates Laboratory, Inc., Reston, VA).

Cooking Loss and Warner-Bratzler Shear Force Determination. Two LM steaks from the sixth to seventh rib section were thawed at 4° C for 24 h. The steaks were weighed and cooked to an internal temperature of 71° C (AMSA, 1995) in a commercial convection oven (Zephaire E model, Blodgett Oven Co., Burlington, VT) preheated at 165° C. End point temperature was monitored using a multichannel data logger (model 245A, VAS Engineering Inc., San Diego, CA) with Teflon-coated thermocouple wires (Type T, Omega Engineering, Inc., Stamford, CT) inserted into the geometric center of each steak. Steaks were turned once, at 35° C, during the cooking process. Steaks were blotted dry with paper towels and weighed. The difference between the precooked and cooked steak weights was divided by the precooked weight to calculate cooking loss percentage.

Steaks were allowed to cool at 2 to 3° C for 2 h after cooking, and a mechanical coring device (Kastner and Henrickson, 1969) was used to remove six 1.27-cm-diameter cores from each steak parallel to the muscle fiber orientation. Cores were sheared perpendicular to the long axis of the core with a Warner-Bratzler shear force device attached to an Instron Universal Testing Machine (model 4466, Instron Corp., Canton, MA) with a 50-kg compression load cell and a 250 mm/min cross head speed. Warner-Bratzler shear values for the 6 cores from each steak were averaged for statistical analysis (AMSA, 1995).

Descriptive Flavor and Aroma Profiles and Texture Attribute Evaluations. Because of the extended (15 mo) storage time, 16 LM steaks (USDA Choice quality grade) were purchased commercially from a local retailer and added to the sensory evaluation session as a reference point. Two weeks before sensory evaluation these steaks were purchased and then wrapped in butcher paper and stored at –20° C until preparation for the sensory panel. On the day before sensory evaluation, steaks were removed from the freezer and thawed at 4° C for 24 h. Steaks were cooked to an internal temperature of 35° C, turned, and then cooked to an end point internal temperature of 71° C on a food service grill (model EG-36H, APW Wyott Food Service Equipment Co., Cheyenne, WY) preheated to 163° C. Internal temperature was monitored by 30-gauge, type-T thermocouples inserted into the geometric center of the steak and attached to a temperature recorder. Each steak was cut into 1.27-cm³ cubes.

This professional descriptive panel (Sensory Science Laboratory, Department of Food Science, University of Arkansas, Fayetteville) had more than 2,000 h of sensory experience, had completed more than 120 h of flavor and texture profile training, and had conducted numerous evaluations of meat products. Sensory panel evaluations were conducted in an environmentally controlled room partitioned into booths with a controlled mixture of red and green light. For orientation, 1 sample was evaluated and discussed at the beginning of each session. For each session, duplicate samples for each treatment were served warm and evaluated by the 8-member panel. Order of presentation was randomized for each panelist within each session.

Flavor characteristics that were evaluated included 1) basic tastes (sweet, salt, sour, and bitter), 2) aromatics (cooked beef, beef fat, blood serum/metallic, browned/caramelized/roasted, degraded protein/fishy, and other flavors). Sweet was defined as the basic taste, stimulated by sugars and high potency sweeteners perceived on the tongue. Salt was defined as the basic taste, stimulated by sodium salt, especially sodium chloride, perceived on the tongue. The basic taste sour is perceived on the tongue and defined as the taste stimulated by acids, such as citric acid. Bitter was defined as the basic taste stimulated by substances such as quinine, caffeine, and certain other alkaloids, perceived on the tongue. Cooked beef was defined as the aromatic associated with cooked beef muscle. Beef fat was defined as the aromatic associated with cooked beef fat. Blood serum/metallic was defined as the aromatic taste sensation associated with raw/rare meat, cooked blood, and blood serum. Browned/caramelized/roasted was defined as a sweet aromatic characteristic of browned sugars and other carbohydrates. Degraded protein/fishy was defined as the aromatic associated with trimethylamine and old fish. The aromatics were also evaluated in the aroma and aftertaste. Aftertaste was defined as the taste that was perceived after the product had been tasted, chewed, and then expelled. The characteristics were scored to the nearest 0.5 on a scale ranging from 0 (least intense) to 15 (most intense).

Texture characteristics that were evaluated included 1) first bite (hardness, cohesiveness, and moisture release) and 2) chewdown (cohesiveness of mass, hardness of mass, fibrousness, and number of chews). Procedures for this panel were in accordance with the guidelines set by the AMSA (1995). Duplicate 2.54 x 1.27 x 1.27-cm samples from each steak were provided to panelists. Hardness was defined as the force required to compress the sample, whereas cohesiveness was defined as the amount the sample deforms rather than splits apart, cracks, or breaks. Moisture release was defined as the amount of wetness, or moistness, felt in the mouth after 1 bite or chew. Cohesiveness of mass was defined as how well the chewed sample holds together; hardness of mass was defined as the force required to compress the sample/bolus after chewing, and fibrousness was defined as the amount of grinding of fibers required to chew through the sample.

Statistical Analysis

Analyses of variance were conducted on growth performance, carcass, and plasma data using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The experimental unit for growth performance was pen, whereas carcass and plasma data utilized animal as the experimental unit. The model included block and dietary treatment. The descriptive flavor and aroma profile data, as well as the texture attribute data, were analyzed using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The model included replication, steak source, and panelist. The experimental unit for the descriptive flavor and aroma profile data, and the texture attribute data, was steak. If steak source was significant (P < 0.10), an F-protected t-test was used to separate the means.

	RESULTS AND DISCUSSION

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

 
Feedlot Performance

Daily feed intake for the entire 70-d study (Table 2) was decreased (P < 0.01) by dietary supplementation of fish oil. Previous research has indicated that feed intake could be depressed when diets contain more than 8% fat because of adverse effects of fat, particularly PUFA, on rumen microbial populations (Rule et al., 1989). However, Wonsil et al. (1994) reported that a diet containing 3% added oil (1.5% fish oil and 1.5% stearic acid) and 7.1% total fat, had no effect on apparent total tract digestibility of DM, ADF, OM, or N. In this trial, dietary fat level was increased to 6.7% with the addition of fish oil. Therefore, the depression in intake was most likely due to several factors, such as palatability, energy density of the diet, and (or) total fat. Scollan et al. (2001) reported that cattle consuming a diet (60:40 forage:concentrate on a DM basis) containing 6% total fat in the diet with 2% from fish oil did not decrease feed intake. However, Whitlock et al. (2002) reported that the addition of 2% fish oil to lactating dairy cow diets decreased feed intake. This result is also supported by Wonsil et al. (1994), who found that the addition of 1.5% fish oil and 1.5% stearic acid to the diet of lactating dairy cows decreased intake from 24.6 kg/d to 21.4 kg/d.

Plasma Fatty Acids

Concerns about consumer intake of fat, particularly SFA, have resulted in closer scrutiny of the fatty acid composition of ruminant products. It has been shown that the C20 and C22 fatty acids of fish oil, even when not protected, are not hydrogenated in the rumen to any significant extent (Ashes et al., 1992). Therefore, it was not surprising that plasma fatty acid profiles taken on d 63 were affected by fish oil supplementation (Table 3). Fatty acid proportions in the present trial are similar to those reported by Ashes et al. (1992). Fish oil supplementation increased (P < 0.01) the proportions of myristic (C14:0), palmitic (C16:0), and palmitoleic (C16:1) acids. Because palmitic acid (C16:0) is thought to be hyperlipidemic and may contribute to increasing serum cholesterol (Lough et al., 1992; Solomon et al., 1992), increasing its proportion would not be desired. In contrast to our study, the proportion of C16:0 in plasma was not affected by feeding ruminally protected fish oil (Ashes et al., 1992) or by feeding fish oil plus stearic acid (Wonsil et al., 1994).

Incorporation of the n-3 fatty acids (C18:3, and C20:5) into beef could make it fit more easily into the diet of a health-conscious consumer because high n-6 to n-3 fatty acid ratios have been accepted as the cause of several health problems (Simopoulos, 2002; Wijendran and Hayes, 2004). Excessive amounts of n-6 PUFA and a very high n-6/n-3 ratio, as found in today’s diets, promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of n-3 PUFA (a low n-6/n-3 ratio) exert suppressive effects (Simopoulos, 2002). However, fish oil supplementation in our trial decreased the concentrations of total PUFA and SFA and increased the concentration of MUFA found in the plasma.

Carcass Characteristics and Chemical Composition of Rib Sections

Fish oil supplementation decreased (P = 0.06) HCW and tended to decrease (P = 0.13) percentage KPH, but LMA, yield grade, dressing percent, marbling, quality grade, and fat thickness did not differ (P > 0.24) between treatments (Table 4). Differences in feed intake and the subsequent numeric decrease in ADG were probably responsible for the effect of fish oil on HCW. Mandell et al. (1997) reported a similar trend in cattle that had been supplemented with fish meal in which cattle that had been supplemented with 10% fish meal had lower hot carcass weights than cattle fed 5% fish meal. However, Scollan et al. (2001) suggested that fish oil supplementation had no effect on cold carcass weight.

Cooked LM steaks from the fish oil-supplemented steers did not differ (P > 0.15) in the basic tastes (sweet, salt, sour, and bitter) from the control or retail products in this study (Table 6). When the flavor aromatics were considered, steaks from the fish oil-supplemented steers did not differ (P > 0.10) in cooked beef, beef fat, blood serum/metallic, or browned/caramelized/roasted flavors. However, fish oil supplementation did increase (P < 0.05) the sensation of degraded protein/fishy flavor compared with the control and retail products. In addition, a difference was detected between the control and retail steaks, confirming a negative correlation between storage time and flavor attributes (Moody et al., 1978).

The panel determined that steaks from fish oil-supplemented steers had less (P < 0.05) cooked beef after-taste than purchased steaks (Table 6). However, panelists did not (P > 0.15) distinguish a difference for the aftertaste between the control and fish oil products. Additionally, panelists did not detect (P > 0.20) differences among the 3 products in aftertaste for the flavors of beef fat, blood serum/metallic, browned/caramelized/roasted, salt, or bitter. However, panelists’ ratings indicated an increase in the aftertaste of degraded protein/fishy; the purchased steaks had the least, steaks from controls intermediate (P < 0.05), and steaks from fish oil-fed steers had the greatest amount (P < 0.05).

The panel did not (P > 0.10) distinguish any differences for the 3 first bite attributes (hardness, cohesiveness of mass, and moisture release; Table 7). However, during chew-down, panelists indicated that steaks from steers supplemented with fish oil had a greater (P < 0.05) hardness of mass and required more (P < 0.05) chews to swallow than did the control or retail steaks. Fish oil supplementation also resulted in increased (P < 0.05) fibrousness between fish oil and retail steaks but not (P = 0.15) between steaks of steers fed control or fish oil diets.

	IMPLICATIONS

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

 
Fish oil supplementation at 3% of the diet as used in this 70-day finishing study would be expected to have no effect on feed efficiency or individual carcass quality characteristics. However, fish oil supplementation would be expected to decrease feed intake and may produce some off-flavors and textures in beef.

	Footnotes

 
¹ Research was funded in part by a grant from the Arkansas Beef Council. Authors thank Omega Protein for the donation of the Menhaden fish oil, and P. Hornsby, J. Sligar, and G. Carte for expert assistance in caring for the cattle.

² Present address: Morehead State University, Morehead, KY 40351.

³ Corresponding author: ekegley{at}uark.edu

Received for publication July 23, 2004. Accepted for publication November 28, 2005.

	LITERATURE CITED

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

 


AMSA. 1995. Research guidelines for cookery, sensory evaluation, and instrumental tenderness measurements of fresh meat. Am. Meat Sci. Assoc., Chicago, IL.

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Ashes, J. R., B. D. Siebert, S. K. Gulati, A. Z. Cuthbertson, and T. W. Scott. 1992. Incorporation of n-3 fatty acids of fish oil into tissue and serum lipids of ruminants. Lipids 27:629–631.[Medline]

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