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ANIMAL PRODUCTS |
* Department of Animal Science, University of Arkansas, Fayetteville 72701;
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Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506;
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Department of Animal Science, University of Wyoming, Laramie 82071
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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0.14). The inclusion of fat in the diet did not (P 0.15) affect carcass characteristics. Steaks from the steers consuming diets with added fat were darker (lower L* value; P < 0.05) than the controls; however, dietary treatments did not (P 0.10) affect any other objective color measurements or discoloration scores during retail display. Thiobarbituric acid reactive substances for LM steaks did not differ (P = 0.21) by dietary treatment. The cooked LM steaks from steers fed poultry fat did not (P 0.80) differ in juiciness or flavor intensity from steaks of steers fed the control or tallow diets. There were also no differences (P = 0.18) in off flavors as a result of added dietary fat. In the LM and adipose tissue, percentages of total SFA were increased (P = 0.05) by adding supplemental fat to the diet, regardless of source. In the LM, total MUFA were decreased (P = 0.02) by adding supplemental fat. Conversely, diet did not (P 0.14) affect the proportions of total PUFA in either tissue or total MUFA in the adipose tissue. Results indicated that replacing beef tallow in finishing diets with poultry fat, a more economical energy source, had no detrimental effects on growth performance, carcass characteristics, retail display life, fatty acid profiles, or palatability.
Key Words: beef quality • cattle • fatty acid • finishing diet • poultry fat
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Fat generally is limited to <5% of the diet to minimize negative effects on feed intake and fiber digestion. These effects differ based on the fatty acid composition of the dietary fat, with PUFA having a more negative impact on cellulytic rumen bacteria (Coppock and Wilks, 1991
; Doreau and Chilliard, 1997); however, because cellulose is low in finishing feedlot cattle diets, this effect may be of lesser importance (Plascencia and Zinn, 2001). Using increasing levels of tallow soap stock, Zinn (1994) proposed that the detrimental effects of high levels of supplemental fat were due to depressed intestinal lipid digestibility.
In the rumen, most triglycerides are hydrolyzed and the unsaturated fatty acids are hydrogenated (Coppock and Wilks, 1991; Doreau and Chilliard, 1997). However, increasing the proportion of n-3 fatty acids in ruminant diets may modify the fatty acid composition of their muscle tissue, indicating that all dietary fatty acids are not completely hydrogenated in the rumen (Scollan et al., 2001). In the future, more emphasis may be placed on the characterization or modification of the fatty acid composition of beef, or both. However, supplementation will need to be economical in order for the producer to remain efficient, and no negative impacts on carcass characteristics, tissue composition, or organoleptic traits should exist. One economical source of dietary fat that may be suitable for feedlot cattle diets is poultry fat. Therefore, our objectives were to determine the effects of dietary poultry fat or tallow on performance, carcass characteristics, beef quality, shelf life, palatability, and fatty acid composition of cattle consuming a finishing diet.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The finishing study was initiated on December 5, 2002, and the initial BW was 411 ± 4.5 kg. Steers were stratified by source, blocked by weight (5 blocks), and assigned to 15 pens that were 3.7 x 29.3 m each (4 steers per pen). Pens were assigned randomly within blocks to 1 of 3 dietary treatments (Table 1) consisting of 1) a corn-soybean meal control diet devoid of added fat; 2) the control diet formulated with 4% tallow; or 3) the control diet formulated with 4% poultry fat. Single lots of poultry fat and tallow were obtained from Tyson Foods Inc. plants in Noel, MO, and Emporia, KS, respectively.
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Steers were weighed on consecutive days at d 0 and 112 to begin and end the trial, and interim weights were collected on d 28, 55, and 83. On d 55, steers were implanted with Revalor-S (Intervet Inc., Millsboro, DE). One steer on the control diet was removed from the study on d 78 due to physical injury.
On d 113, steers were transported approximately 579 km to a commercial beef processing plant and slaughtered after a 12-h rest period. Carcasses were identified individually, and HCW were recorded. After a 24-h conventional spray-chill, carcass yield and quality grade were evaluated by trained university personnel. Bone-in rib sections from the left sides were obtained in the holding cooler after being graded, vacuum-packaged, boxed, and transported under refrigeration back to the University of Arkansas Red Meat Abattoir for further processing.
At approximately 48 h postmortem, rib sections were deboned and seven 2.54-cm-thick LM steaks were cut from each rib section. Beginning at the posterior end of each rib (12th rib), 2 steaks were vacuum-packaged for Warner-Bratzler shear force, 2 were cut and vacuum-packaged for sensory evaluation, 2 were cut and packaged for retail display, and 1 was cut and packaged for fatty acid analysis. A portion of subcutaneous fat was also taken from each rib section for fatty acid analysis. Steaks for Warner-Bratzler shear force and sensory evaluation were stored at –20°C until analysis.
Warner-Bratzler Shear Force
Steaks were thawed at 4°C for 24 h, weighed, and then cooked to an internal temperature of 71°C in a preheated, commercial convection oven (Zephaire E model, G. S. Blodgett Co., Burlington, VT) with an oven temperature of 165°C. Temperatures were 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. When steaks reached an internal temperature of 35°C they were turned once.
After cooking, steaks were blotted dry on paper towels and reweighed to calculate cooking loss percentage and then were allowed to cool to room temperature. Six 1.27-cm-diam. cores were removed from each steak parallel to the muscle fiber orientation with a mechanical coring device. Each core was sheared once through the center with a Warner-Bratzler shear device attached to an Instron Universal testing machine (model 4466, Instron Corporation, Canton, MA) with a 50-kg load cell and a crosshead speed of 250 mm/min (AMSA, 1995). The peak shear force values of the 6 cores from each steak were averaged for statistical analysis.
Sensory Panel Evaluations
Steaks for sensory evaluations were thawed at 2°C for 24 h in vacuum-packaged bags. Steaks were then cooked in a Blodgett oven (model DFG-102, G. S. Blodgett Co.) preheated to 163°C. Thermocouple wires (30-ga. copper and constantan; Omega Engineering, Stamford, CT) were inserted into the geometric center of each steak and the internal temperature was monitored using a Doric Minitrend 205 (VAS Engineering, San Francisco, CA). Steaks were turned over at 35°C and removed from the oven when the internal temperature reached 71°C. The procedures for training panelists were in accordance with AMSA (1995) guidelines.
Cooked steaks were cut into 1.25 x 1.25-cm cubes, placed in double boilers with the lower portion containing water, and held on burners set to 107°C. Each panelist received 2 cubes in random order. Panelists did not receive samples from more than 8 steaks per session. Panelists were provided unsalted saltine crackers (Nabisco Inc., East Hanover, NJ) and filtered water (The Brita Products Company, Oakland, CA) to cleanse their palates between samples. Traits evaluated by the sensory panel included juiciness, beef flavor intensity, off-flavor intensity, connective tissue amount, myofibrillar tenderness, and overall tenderness (1 = extremely dry, bland, intense, abundant, extremely tough, and extremely tough to 8 = extremely juicy, intense, none, none, extremely tender, and extremely tender; AMSA, 1995).
Retail Display
Two steaks were placed on foam trays, over-wrapped with an oxygen-permeable PVC film, and allotted randomly to 0 or 7 d of retail display. Packaged steaks were placed in open-topped, coffin-chest display cases (model LMG12, Tyler Refrigeration Corp., Niles, MI) maintained at an average temperature of 2.6°C. Steaks were displayed under continuous, 1,600 lx of deluxe, warm-white, fluorescent lighting (bulb type: F4OT12, 40-W; Phillips Inc., Somerset, NJ).
Steak color was measured on d 0, 1, 4, and 7 of retail display. On each day of display, L* (a measure of darkness to lightness; a larger number indicates a lighter color), a* (a measure of redness; a larger number indicates a more red color), and b* (a measure of yellowness; a larger number indicates a more yellow color) values were determined from 4 random readings with a Hunter MiniScan XE (model 45/0-L, 25-mm aperture; Hunter Associates Laboratory, Reston, VA) using illuminant C. Additionally, the hue angle (a measure of the distance, in degrees, from the true red axis) was calculated as tan–1(b*/a*), whereas chroma (a measure of the total color, or vividness of color) was calculated as (a*2 + b*2)
. The ratio of reflectance measured at 630 nm to 580 nm was used to estimate the oxymyogloblin concentration of steaks during retail display. A 3-person panel also evaluated each steak for discoloration (1 = total discoloration to 7 = no discoloration; Pohlman et al., 2002) on d 0, 1, 3, 5, and 7 of display.
After color data collection on d 0 and 7 of display, the steaks were removed from the packaging material, and an approximately 5-g cross-section of LM was removed from the center of each steak for analysis of thiobarbituric acid reactive substances (TBARS) according to procedures outlined by Witte et al. (1970). Values for TBARS are reported as milligrams of malenaldehyde per kilogram of muscle.
Fatty Acid Profiles
Duplicate 30-g feed samples were pulverized in liquid nitrogen in a Waring blender (model 38BL54, Waring Commercial, New Hartford, CT), freeze dried (model 4.5, Labconco Corp., Kansas City, MO), and stored in airtight bags at –20°C until analysis. Additionally, 150-mg samples of feed, adipose tissue, or LM were subjected to transesterification by incubating in 2.0 mL of 0.2 M methanolic KOH in 16 x 125-mm screw-cap tubes at 50°C for 30 min, with vortex-mixing 2 to 3 times/ min until the samples were dissolved (Murrieta et al., 2003). The tubes were allowed to cool to room temperature, and 1 mL of saturated NaCl was added to each. Two milliliters of hexane, containing an internal standard (methyl 13:0, 0.5 mg/mL), was added to the tubes, which were then vortexed and centrifuged for 5 min at 1,100 x g to separate the phases.
Fatty acid methyl esters (FAME) were transferred to GLC vials that contained a 1.0-mm bed of anhydrous sodium sulfate. Separation of FAME was achieved by GLC (model 6890N with Chemstation software, [Agilent Technologies Inc., Wilmington, DE] and an automatic sample injector) with a 100-m capillary column (Supelco 2560 Fused Silica Capillary column, Supelco Park, Bellefonte, PA) and He as a carrier gas at 0.5 mL/min. Oven temperature was maintained at 175°C for 40 min and then ramped at 10°C/min to 240°C. Injector and detector temperatures were 250°C, and identification of FAME peaks was accomplished using purified standards (Nu-Chek Prep, Elysian, MN, and Matreya, Pleasant Gap, PA).
Statistical Analysis
Data were analyzed as a completely randomized block design. Analyses of growth performance, carcass characteristics, and fatty acid data were conducted with the MIXED models procedure of SAS (SAS Inst. Inc., Cary, NC), with pen as the experimental unit. This model included dietary treatment as the fixed effect and block specified as the random effect. The model for retail display data included the fixed effects of dietary treatment, day, and the day x dietary treatment interaction, whereas block and the block x dietary treatment interaction were specified as random effects. The model for sensory-panel data included dietary treatment, panelist, and the dietary treatment by panelist interaction as fixed effects, and block and the block x dietary treatment as random effects. If treatment was significant (P < 0.05), then an F-protected Student’s t-test (PDIFF option) was used to separate least squares means.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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) from d 0 to 28 (P = 0.26) or from d 0 to 55 (P = 0.13). Steers fed the poultry fat diet had greater (P < 0.05) ADG than steers fed the control or the tallow diet from d 0 to 83. However, for the entire 112-d study, dietary treatments did not affect ADG (P = 0.17). Other researchers have reported improved ADG with fat supplementation of finishing diets with 5% as yellow grease or griddle grease (Plascencia et al., 1999) and 3.5% as soybean oil, tallow, or yellow grease (Brandt and Anderson, 1990). Likewise, Zinn and Plascencia (1996) and Scollan et al. (2001) reported that feeding fat had no negative impact on growth performance.
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; Krehbiel et al., 1995), including fat in the diet reduced (P < 0.05) ADFI of steers after 28, 55, and 83 d on feed compared with steers fed the control diet (Table 2
). However, this was inconsistent with the findings of Plascencia et al. (1999), who found an increase in DMI during the first 56 d of their trial and no effect of fat supplementation on DMI for the entire 144 d trial. Over the entire 112-d feeding period, steers fed 4% beef tallow consumed less (P = 0.01) feed than the steers fed the control diet; however, ADFI of steers fed 4% poultry fat tended to be lower than that of the steers fed the control (P = 0.06) diet and did not differ from ADFI of steers fed the tallow (P = 0.36) diet. Choi et al. (2000) observed a linear depression in feed intake of dairy cows as supplemental fat (as Ca-salts of long chain fatty acids) increased from 0 to 9%. Dietary fat decreased abomasal motility (Nicholson and Omer, 1983), and increased cholecystokinin release (Choi and Palmquist, 1996). However, feeding value of fat may be influenced by the unsaturated-to-saturated fatty acid ratio, and this ratio may determine the impact of fat on intake and digestion.
As documented in previous experiments (Zinn and Plascencia, 1996; Plascencia et al., 1999; Ramirez and Zinn, 2000), including fat in a finishing diet improved G:F. In the current study, addition of fat to the finishing diet had no effect (P = 0.89) during the first 28 d of the trial (Table 2). However, when compared at 55 d, steers fed fat had greater (P < 0.05) G:F over controls, and the steers fed poultry fat had greater (P < 0.05) G:F than steers fed the tallow diet. When compared at d 83, steers consuming the poultry fat diet were the most efficient (P < 0.01), whereas control and tallow-fed steers did not differ in G:F (P = 0.25). Moreover, when diets were compared at d 112, steers fed the diet containing poultry fat had a 14.8% improvement (P < 0.05) in G:F when compared with the steers fed the control diet, and tallow-fed steers were intermediate. Zinn et al. (2000) reported that intestinal digestibility of total fatty acids was inversely related to biohydrogenation; therefore, in the present trial the tallow might have been less digestible than the poultry fat. However, Huffman et al. (1992) fed cattle an animal fat or a more unsaturated animal fat:vegetable oil blend in a series of trials and did not observe consistent differences in digestibility of the fat types or cattle performance.
Dietary treatment did not affect carcass weight (P = 0.15) or LM area (P = 0.16; Table 3). Inclusion of fat, regardless of source, in the diet of finishing steers did not (P 0.36) affect fat thickness, internal fat percentage, yield grade, marbling score, or quality grade. In some previously published research, fat supplementation to finishing diets increased the percentage of internal fat (Zinn, 1989; Clary et al., 1993; Plascencia et al., 1999), fat thickness (Brandt and Anderson, 1990; Bock et al., 1991), and marbling score (Zinn, 1989; Zinn and Plascencia, 1996). However, Clary et al. (1993) observed decreased marbling scores with supplemental fat, and other trials have reported that supplemental fat did not affect marbling scores (Zinn, 1988; Bock et al., 1991; Krehbiel et al., 1995), internal fat percentages (Bock et al., 1991), or fat thicknesses (Zinn, 1988; Krehbiel et al., 1995).
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). However, steaks from steers fed the diets with added fat had greater (P < 0.05) Warner-Bratzler shear force values than steaks from steers fed the control diet. In general, fat supplementation typically has not affected tenderness or water retention of muscle (Doreau and Chilliard, 1997).
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0.80) differ in juiciness and flavor intensity from steaks of steers fed the control or tallow diets (Table 4). Moreover, panelists did not detect any differences in myofibrillar or overall tenderness, as well as perceived connective tissue, of the steaks (P 0.28), even though Warner-Bratzler shear force values from steers fed poultry fat or tallow were greater (P < 0.05) than controls. Whereas some studies show that there can be differences in flavor of beef from cattle fed diets supplemented with fat (Wood et al., 2003), there were no differences (P 0.18) in off-flavors as a result of added dietary fat in the current study. Changes observed in the fatty acid profiles were not detected by the panelists.
There were no (P 0.10) dietary fat source x day interactions; therefore, only main effects will be reported for retail display results. Steaks from steers fed the tallow and the poultry fat diets were darker (lower L* value; P < 0.05) than controls (Table 5). However, dietary treatments did not (P 0.10) affect other objective color measurements or discoloration scores during retail display. Beef was less red (lower a* value; P < 0.01) and yellow (lower b* value; P < 0.01) on d 5 of retail display (Table 6) compared with d 0, 1, or 3; and by d 7 steaks were the least (P < 0.01) red and yellow. The greatest (P < 0.01) hue angle and the lowest (P < 0.01) chroma and 630/580 nm reflectance ratio were observed on d 7 of retail display, with discoloration score decreasing as time on display increased (d 1 > 3 and d 5 > 7; P < 0.01).
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). In addition, this reaction generally proceeds in parallel to that of rancidity (Wood et al., 2003). However, to our knowledge, there have been few color studies reported on beef from cattle fed different fat sources. Wistuba et al. (2002) found that color was not affected by the addition of fish oil to finishing cattle diets, although Vatansever et al. (2000) detected faster color deterioration for steaks from calves fed fish oil. Yet Ponnampalam et al. (2001) reported no consistent changes in the color of lamb with the addition of elevated omega-3 and omega-6 fatty acids to diets.
Concentrations of TBARS in the LM of steers consuming diets formulated with fat did not differ (P = 0.21). Ponnampalam et al. (2001) also reported that TBARS concentrations demonstrated that enrichment of lamb-muscle PUFA through dietary manipulation did not result in any differences in lipid oxidative stability of fresh or vacuum-packaged lamb over a 6-d display period. An effect of fatty acids on shelf life is explained by the propensity of unsaturated fatty acids to oxidize, leading to the development of rancidity as display time increases (Wood et al., 2003). By d 7 of retail display, TBARS concentrations of the LM in the current study averaged 0.78 mg/kg. As the TBARS concentration nears 1.0 mg/kg, products become less accepted by consumers (Younathan and Watts, 1959). With the onset of lipid oxidation, meat typically becomes discolored because lipid and pigment oxidation are closely coupled in beef (an increase in one of these results in a similar increase in the other; Faustman and Cassens, 1990). Neither TBARS (P = 0.21) nor beef discoloration during retail display (P = 0.53) were increased in beef from steers fed diets with added fat in the current study.
In the LM, percentages of total SFA were increased (P = 0.05) by feeding supplemental fat from either source (Table 7). Furthermore, percentages of total MUFA were decreased (P = 0.02) by the addition of fat to finishing diets, regardless of source. However, percentages of total PUFA in the LM were not (P = 0.86) affected by diets. Brandt and Anderson (1990) also observed an increased percentage of SFA and a decreased percentage of unsaturated fatty acids when steers were fed supplemental tallow.
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). Additionally, the LM of steers fed poultry fat had an increased (P < 0.05) proportion of stearic acid (18:0) than the LM of steers fed the control diet, with 18:0 proportions in the LM of steers fed tallow being intermediate. Bock et al. (1991) observed increased concentrations of 18:0 in the intermuscular fat, but not the LM, of steers fed supplemental tallow or soybean oil soapstock. Ferlay et al. (1993) reported decreased concentrations of odd-numbered chain (15 and 17 C) fatty acids in the bacterial fraction of cows fed supplemental fat, possibly due to incorporation of the dietary fatty acids as free fatty acid vacuoles (Bauchart et al., 1990). Given that, Jenkins (1993, 1994) summarized that odd chain fatty acids are produced de novo by rumen bacteria with propionate substituting for an acetate building block. Thus, increased uptake of exogenous lipid by microbial cells would lead to decreased de novo fatty acid synthesis (Demeyer et al., 1978) and result in fewer odd chain fatty acids present in the lower gut for absorption and deposition in the muscle of the steers fed the diet with added poultry fat.
The proportions of total SFA and myristic acid (14:0) in the s.c. adipose tissue were increased (P = 0.05) by the addition of either fat source to the finishing diet (Table 8). However, adipose tissue from steers that consumed the diet with added poultry fat had lower (P < 0.05) proportions of heptadecanoic acid (17:0) than adipose tissue from steers fed the control or tallow-supplemented diets. Steers that consumed the control diet had greater heptadecenoic acid (17:1) proportions in the adipose tissue than (P < 0.05) steers fed both sources of fat, and steers fed tallow had greater proportions (P < 0.05) than steers fed poultry fat. However, diet did not (P 0.14) affect percentages of the total MUFA or PUFA in the adipose tissue.
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, the saturated:unsaturated fatty acid ratio tended to be increased by the supplemental animal fats in the LM (P = 0.06) and adipose (P = 0.08) tissues. The total trans fatty acids also tended to be increased in the LM (P = 0.09) and adipose (P = 0.07) tissues of steers fed poultry fat. In conclusion, results of the current study indicated that replacing beef tallow in finishing diets with a more economical energy source, poultry fat, had no detrimental effects on growth performance, carcass characteristics, beef quality, or palatability. Compared with the control (corn/soybean meal) diet, fat supplementation with either tallow or poultry fat increased the proportion of total SFA in the muscle and adipose tissue; however, there were minimal differences in fatty acid composition of tissues from steers fed poultry fat compared with those of steers fed tallow. Therefore, poultry fat may be used in place of beef tallow in finishing diets of feedlot cattle.
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Footnotes |
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2 Present address: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506.
4 Present address: Morehead State University, Morehead, KY 40351.
3 Corresponding author: ekegley{at}uark.edu
Received for publication August 16, 2005. Accepted for publication April 6, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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