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Interactive effect of ractopamine and dietary fat source on pork quality characteristics of fresh pork chops during simulated retail display¹

J. K. Apple^*,2, C. V. Maxwell^*, B. R. Kutz^*, L. K. Rakes^*, J. T. Sawyer^*, Z. B. Johnson^*, T. A. Armstrong, S. N. Carr and P. D. Matzat

^* Department of Animal Science, University of Arkansas, Fayetteville 72701; and Elanco Animal Health, a Division of Eli Lilly and Company, Greenfield, IN 46140

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION LITERATURE CITED

 
Crossbred pigs (n = 216) were used to test the interactive effect, if any, of ractopamine (RAC) and dietary fat source on the performance of finishing pigs, pork carcass characteristics, and quality of LM chops during 5 d of simulated retail display (2.6°C and 1,600 lx warm-white fluorescent lighting). Pigs were blocked by BW and allotted randomly to pens (6 pigs/pen), and, after receiving a common diet devoid of RAC for 2 wk, pens within blocks were assigned randomly to 1 of 4 diets in a 2 x 2 factorial arrangement, with 5% fat [beef tallow (BT) vs. soybean oil (SBO)] and RAC (0 vs. 10 mg/kg). Diets were formulated to contain 3.1 g of lysine/Mcal of ME and 3.48 Mcal/kg of ME. Across the entire 35-d trial, pigs fed RAC had greater (P < 0.01) ADG and G:F, but RAC did not affect (P = 0.09) ADFI; however, performance was not affected (P 0.07) by dietary fat source. Carcass weight, LM depth, and lean muscle yield were increased (P < 0.01), whereas fat depth was decreased (P = 0.01), in carcasses from RAC-fed pigs; however, carcass composition measures were similar (P 0.27) between fat sources. Feeding 10 mg/kg of RAC reduced (P 0.04) the proportions of SFA and MUFA and increased (P < 0.01) the proportion of PUFA and the iodine value, in pork backfat. Conversely, backfat from carcasses of BT-fed pigs had greater (P < 0.01) percentages of SFA and MUFA, and lower (P < 0.01) percentages of PUFA, than backfat from SBO-fed pigs. Moreover, the PUFA:SFA and iodine value were considerably reduced (P < 0.01) by including BT in swine finishing diets. The LM from pigs fed RAC had greater pH values (P = 0.03) and received greater (P 0.01) American and Japanese color scores during retail display. The LM from RAC-fed pigs had lower (P 0.02) L*, a*, and b* values, whereas the LM of SBO-fed pigs received greater (P < 0.01) subjective color scores and b* values, as well as lower L* values, than the LM of BT-fed pigs. Across the 5-d display period, oxidative rancidity was not affected by dietary RAC (P = 0.58) or fat source (P = 0.47). Neither RAC nor fat source altered LM cooking losses and shear force values. Feeding 10 mg/kg of RAC will improve rate and efficiency of gain, carcass composition, and LM quality. And, even though fatty acid composition of backfat samples was altered by dietary fat source, performance and carcass composition, as well as quality during 5 d of retail display, were similar when pigs were fed diets formulated with BT or SBO.

Key Words: carcass composition • color • fatty acid composition • pork • ractopamine • retail display

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION LITERATURE CITED

 
It has been repeatedly shown that including ractopamine hydrochloride (RAC; Elanco Animal Health, Greenfield, IN) in swine finishing diets results in improved growth rates. In a summary of 6 research trials, Watkins et al. (1990) reported that feeding RAC improved ADG, regardless of dietary concentration, and Jones et al. (2000), summarizing results of 20 trials, also demonstrated that dietary inclusion of RAC increased ADG over untreated controls. Moreover, it is evident that increasing dietary energy improves feed efficiency in nonRAC- and RAC-fed pigs (Williams et al., 1994; Dunshea et al., 1998); yet, in the aforementioned studies, a single fat source was used to elevate dietary energy density, and little information is available comparing different fat sources in diets containing RAC.

Soft pork fat has become an economical concern of the US pork industry (Irie, 1999); negatively impacting carcass handling and fabrication, further processing yields, product attractiveness, shelf-life, and exportability (Morgan et al., 1994). Factors contributing to the increased incidence of soft fat include the adoption of lean genetics (Wood et al., 1989; Sather et al., 1995) and the inclusion of polyunsaturated fat sources (Warnants et al., 1999; Gatlin et al., 2003; King et al., 2004). Moreover, including RAC in swine finishing diets produces leaner, more muscular carcasses (See et al., 2004; Weber et al., 2006) and elevates the levels of PUFA in carcass fat depots (Carr et al., 2005b; Xi et al., 2005; Weber et al., 2006). Lastly, there are no studies reporting the quality shelf-life of pork from RAC-fed pigs during retail display. Therefore, the objective of this study was to determine the interactive effects, if any, of RAC and dietary fat source on the performance and pork carcass composition of finishing pigs, as well as LM quality during 5 d of simulated retail display.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION LITERATURE CITED

 
Animal care and experimental protocols were approved by the University of Arkansas Interdepartmental Animal Care and Use Committee before initiation of this experiment.

Animals and Diets

Crossbred barrows and gilts (n = 216), from the mating of line 348 sows to EB boars (Monsanto Choice Genetics, St. Louis, MO), were blocked by BW (77.6 ± 6.5 kg) into 9 blocks (24 pigs/block) and allotted randomly to pens of 6 pigs within blocks (4 gilts and 2 barrows/pen in blocks 1, 3, and 6; 3 gilts and 3 barrows/pen in blocks 2, 4, and 5; and 2 gilts and 4 barrows/pen in blocks 7, 8, and 9). After a 2-wk adjustment period when all pigs were fed a common finishing diet devoid of RAC (Table 1), pens within blocks were assigned randomly to 1 of 4 dietary treatments in a 2 x 2 factorial arrangement, with 2 RAC levels (0 or 10 mg/kg) and 5% dietary fat from 2 sources (beef tallow or soybean oil). Soybean oil (SBO) and beef tallow (BT) diets contained 3.59 and 3.55 Mcal/kg of ME, respectively; however, lysine concentrations were adjusted to maintain the lysine-to-energy ratio (3.1 g of lysine/Mcal of ME) constant for the 2 fat sources (Table 1). Proportions of SFA, MUFA, and PUFA were 15.90, 24.44, and 58.95%, respectively, in the SBO source and 47.22, 44.88, and 4.05%, respectively, in the BT source (Table 2). Moreover, linoleic (18:2n-6) and linolenic (18:3n-3) acid concentrations were substantially greater, and the proportion of palmitic (16:0) and stearic (18:0) acids was much less, in the SBO- than the BT-diet, resulting in PUFA:SFA and iodine value (IV) of 3.74 and 127.44, respectively, for SBO-diets and 0.72 and 73.47, respectively, for the BT-diet (Table 2). All diets met or exceeded NRC (1998) requirements for 79.5- to 109.1-kg pigs. Additionally, pigs were housed in a curtain-sided building with slatted floors, and each pen was equipped with a single-opening feeder and nipple waterer, which allowed ad libitum access to diets and water throughout the trial. Individual pig BW and feed disappearance were recorded at 7-d intervals during the 35-d feeding trial to calculate ADG, ADFI, and G:F.

Pork Loin Fabrication and Simulated Retail Display

Upon arrival, the blade and sirloin sections were removed from each loin, and center-cut loins were further processed into 1) two 2.5-cm-thick, closely-trimmed (0.64-cm external fat thickness), deboned chops designated for retail display; 2) two 3.8-cm-thick chops used for drip loss determination according to a modified suspension procedure of Honikel et al. (1986); and 3) two 2.5-cm-thick chops used for Warner-Bratzler shear force (WBSF) determinations, with one randomly selected chop immediately frozen at –20°C and the other chop aged an additional 7 d at 4°C. After core removal for drip loss measurements, 2 g of the remaining LM was homogenized in 20 mL of distilled, deionized water, and the pH of the homogenate was measured with a temperature-compensating, combination electrode (Model 300731.1; Denver Instrument Co., Arvada, CO) attached to a pH/Ion/FET-meter (Model AP25; Denver Instrument Co.).

Simulated Retail Display

Before fabrication, a subsample of pork loins was selected at random from each treatment combination (n = 21/treatment), with the goal of at least 2 loins from each pen. From the selected loins, the 2 closely trimmed, boneless, 2.5-cm-thick chops were placed on individual styrofoam trays (with an absorbent pad), and overwrapped with oxygen-permeable, PVC film (O₂ transmission rate = 14,000 mL/m²/24 h at 1 atm; Borden Inc., Dallas, TX). Subsequently, packaged chops were placed in open-topped, coffin-chest display cases (LMG12; Tyler Refrigeration Corp., Niles, MI) maintained at an average temperature of 2.6°C. Chops were displayed under continuous, 1,600 lx of deluxe warm-white, fluorescent lighting (bulb type: F40T12, 40-W; Phillips Inc., Somerset, NJ).

On d 0, 1, 3, and 5 of retail display, chops were visually evaluated for marbling [1 = devoid (1% i.m. lipid) to 10 = abundant (10% i.m. lipid); NPPC, 1999], and color based on both the American (1 = pale, pinkish gray to 6 = dark purplish red; NPPC, 1999) and Japanese color standards (Nakai et al., 1975). In addition to the subjective pork quality measures, L*, a*, and b* values were determined from a mean of 3 random readings made with a Hunter MiniScan XE (45/0-L; Hunter Associates Laboratory, Reston, VA) using illuminant C and a 25-mm view diameter. The spectrocolorimeter was calibrated daily against a standard white tile (M04207; Hunter Associates Laboratory). The hue angle (representing a change from the true red axis) was calculated as tan^–1 (b*/a*), whereas chroma, or saturation index (representing the total color, or vividness, of the LM), was calculated as

Warner-Bratzler Shear Force Determination

Longissimus muscle chops were thawed for 16 h at 2°C, then weighed, and cooked to an internal temperature of 71°C in a commercial convection oven (Zephaire E model; Blodgett Oven Co., Burlington, VT) preheated to 165°C. Internal temperature was monitored with Teflon-coated thermocouple wires (Type T; Omega Engineering Inc., Stamford, CT) placed into the geometric center of each LM chop and attached to a multichannel data logger (model 245A, VAS Engineering Inc., San Diego, CA). Chops were turned once during the cooking process when internal temperature reached 35°C. Immediately after removal from the oven, chops were blotted dry on paper towels and weighed, and the difference between precooked and cooked weights was used to calculate cooking loss percentage. Chops were allowed to cool to room temperature, and five 1.27-cm-diameter cores were removed parallel to the muscle fiber orientation. Then, each core was sheared once through the center with a Warner-Bratzler shear force device attached to an Instron Universal Testing Machine (model 4466, Instron Corp., Canton, MA) with a 55-kg tension/compression load cell and a crosshead speed of 250 mm/min.

Fatty Acid Analysis

Five days after slaughter, frozen backfat cores were weighed, placed in 30-mL beakers, and reweighed. Beakers were then placed into vacuum-flasks attached to the manifold of a Labconco freeze-dryer (model 4.5, Labconco Corp., Kansas City, MO) with a temperature setting of –50°C and a vacuum of less than 10 µM of Hg. Samples were freeze-dried for 60 h, beakers were reweighed, and the difference between initial and dried beaker weights was used to calculate percent moisture.

Duplicate 30-mg freeze-dried backfat samples, as well as pulverized samples of diets and each fat source, were subjected to direct 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 tissue was dissolved (Murrieta et al., 2003). Tubes were allowed to cool to room temperature, and 1 mL of saturated NaCl was added to each tube. Then, 2 mL of hexane containing 0.5 mg/mL of an internal standard (methyl 13:0) was added to tubes, tubes were vortexed, and subsequently centrifuged for 5 min at 1,100 x g to separate phases.

Fatty acid methyl esters (FAME) were transferred to GLC vials that contained 1.0-mm bed of anhydrous sodium sulfate. Separation of FAME was achieved by GLC [model 5890 Series II GC with automatic sample injector (HP-7673) and HP-3365 software; Hewlett-Packard, Avondale, PA] equipped with a 100-m capillary column (0.25-mm internal diameter, model 2560 Fused Silica Capillary, Supelco Inc., Bellefonte, PA) and He as the carrier gas (0.5 mL/min). Oven temperature was maintained at 175°C for 35 min, ramped at 5°C/min to 215°C, and then ramped at 10°C/min to 235°C, whereas injector and detector temperatures were maintained at 250°C. Identification of peaks was accomplished using purified standards obtained from Nu-Chek Prep (Elysian, MN) and Matreya (Pleasant Gap, PA). The PUFA:SFA ratio was calculated using the formula of Enser et al. (2000) ([18:2n-6] + [18:3n-3]) ÷ ([12:0] + [14:0] + [16:0] + [18:0]), whereas IV was calculated according to the AOCS (1998) equation: (0.95 x [16:1]) + (0.86 x [18:1]) + (1.732 x [18:2]) + (2.616 x [18:3]) + (0.785 x [20:1]).

Statistical Analysis

Performance, carcass composition/quality, and fatty acid composition data were analyzed as a randomized complete block design, with treatments in a 2 x 2 factorial arrangement, blocks based on initial BW, and pen as the experimental unit. An ANOVA was generated using the GLM procedure (SAS Inst. Inc., Cary, NC), with the main effects of RAC level (0 vs. 10 mg/kg) and dietary fat source (BT vs. SBO), as well as the RAC x fat source interaction, included in the statistical model. Conversely, LM quality data, collected during simulated retail display, were analyzed as repeated measures using the mixed model procedure of SAS, with display day as the repeated variable and pork loin as the repeated subject. The experimental unit for the ANOVA of the display data was also pen, and fixed (main) effects included in the model were RAC, fat source, and display day, as well as the 2- and 3-way interactions, whereas block was included in the model as the random effect. Least squares means were computed for main and interactive effects and were separated statistically using F-protected (P < 0.05) t-tests (PDIFF option).

	RESULTS AND DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION LITERATURE CITED

 
Swine Performance

There were no (P 0.13) RAC x dietary fat source interactions for ADG, ADFI, or G:F. Even though ADG did not (P 0.11) differ between SBO- and BT-fed pigs during the 35-d feeding trial, RAC-fed pigs had greater (P < 0.05) ADG than controls between 0 and 7 d and 7 and 14 d; yet, ADG, regardless of RAC treatment, was considerably curtailed during the 2nd week of the experiment (Table 3). The observed reduction in ADG was in response of an outbreak of viral diarrhea, and it was speculated that the outbreak either affected the untreated pigs earlier or control pigs responded to antibiotic treatment more quickly because, during the 3rd week (14 to 21 d) of the experiment, ADG was greater (P < 0.05) in control than RAC-fed pigs. Lastly, during the 4th week, and across the entire 35-d feeding period, pigs fed RAC had greater (P 0.01) ADG than untreated pigs. Although ADG was affected during the 2nd and 3rd weeks of the experiment, BW of RAC-fed pigs were heavier (P 0.02) than control pigs during the experiment.

The consensus of available literature has established that supplementing late-finishing diets with 5 (Armstrong et al., 2004, 2005), 10 (See et al., 2004; Weber et al., 2006), or 20 mg RAC/kg of diet (Xiao et al., 1999; Armstrong et al., 2004) increases swine growth rate. Even though Carr et al. (2005b), Mimbs et al. (2005), and Brumm et al. (2004) reported that including 10 mg/kg of RAC in swine diets reduced ADFI, others failed to detect an effect of RAC on feed intake (Crome et al., 1996; Marchant-Forde et al., 2003). Because RAC has been shown to effectively repartition energy from fat deposition (Dunshea et al., 1993) to increased protein synthesis (Bergen et al., 1989) and lean tissue deposition is more energetically efficient than fat deposition (de Lange et al., 2001), it is not surprising that results of this study corroborate the findings that efficiency of growth is improved by feeding 5 (Armstrong et al., 2004, 2005), 10 (Carr et al., 2005b; Mimbs et al., 2005), and 20 mg of RAC/kg of diet (Xiao et al., 1999; Armstrong et al., 2004).

Increasing the energy density of swine diets by fat/oil supplementation has been shown to have no affect on ADG, but depresses ADFI, resulting in improvements in feed efficiency (Campbell and Taverner, 1986; Southern et al., 1989; Weber et al., 2006). However, Weber et al. (2006) reported that performance was similar between pigs fed 5% choice white grease or 5% beef tallow. Even though pig performance was elevated by feeding diets formulated with 6% fat, Engel et al. (2001) reported that ADG, ADFI, and G:F were similar between diets formulated with choice white grease or poultry fat. Moreover, the performance of finishing pigs has been shown to be similar in studies comparing tallow to linseed oil (Kouba et al., 2003), corn oil (Kouba and Mourot, 1999), and soybean oil (Nichols et al., 1991). (P = 0.47). Carcasses from RAC-fed pigs were heavier (P < 0.01) than carcasses from untreated pigs (Table 4). Moreover, including RAC in the finishing diet effectively reduced (P = 0.01) 10th-rib fat depth, and increased (P < 0.01) LM depth and calculated FFLY.

No RAC x dietary fat source interactions were observed for pork carcass cutability traits (P 0.26), ultimate (48-h) LM pH (P = 0.51), or drip loss percentage (P = 0.47). Carcasses from RAC-fed pigs were heavier (P < 0.01) than carcasses from untreated pigs (Table 4). Moreover, including RAC in the finishing diet effectively reduced (P = 0.01) 10th-rib fat depth, and increased (P < 0.01) LM depth and calculated FFLY.

Feeding RAC is generally thought to repartition nutrients from lipogenesis to increased protein synthesis and accretion, and the majority of literature indicates that feeding 10 mg/kg of RAC effectively increased LM area (Carr et al., 2005a, b; Weber et al., 2006) and LM depth (Brumm et al., 2004), resulting in increased calculated (See et al., 2004; Weber et al., 2006) or dissected (Xiao et al., 1999) fat-free muscle percentage. Several researchers have demonstrated that neither 10 (Carr et al., 2005a; Weber et al., 2006) nor 20 mg of RAC/kg of diet (Schinckel et al., 2003; Armstrong et al., 2004) altered backfat depth; however, the observation that 10th-rib fat depth was reduced in carcasses from pigs fed 10 mg/kg of RAC is consistent with the results of Carr et al. (2005b), See et al. (2004), and Marchant-Forde et al. (2003).

Carcass weight, fat and LM depths, and estimated FFLY were similar (P 0.27) between pigs fed SBO and BT (Table 4). These results are in general agreement with other studies that compared dietary fat sources. Carcass weights were similar between pigs fed diets formulated with beef tallow, corn oil (Kouba and Mourot, 1999; Corino et al., 2002), or canola oil (Corino et al., 2002). Engel et al. (2001) failed to detect differences in carcass weight, 10th-rib fat depth, and LM area between pigs fed choice white grease or poultry fat, whereas 10th-rib fat thickness was similar in carcasses of pigs fed 10% animal fat, safflower oil, sunflower oil, or canola oil (Miller et al., 1990). Furthermore, neither choice white grease nor poultry fat altered lean yield estimates (Engel et al., 2001), whereas the percentage of actual carcass (dissected) lean did not differ among pigs fed pork fat, olive oil, or SBO (Scheeder et al., 2000)

Ultimate (48-h) LM pH was greater (P = 0.03) in carcasses from RAC-fed than control-fed pigs; however, LM pH did not (P = 0.10) differ between carcasses from SBO- and BT-fed pigs (Table 4). Although Aalhus et al. (1990) reported that LM pH, measured at 45 min postmortem, was elevated in pigs fed 10 mg/kg of RAC, there is no previously published information supporting the observed increase in ultimate LM pH by feeding 10 (Carr et al., 2005a, b; Weber et al., 2006) or 20 mg of RAC/kg of diet (Dunshea et al., 1993; Carr et al., 2005a). Additionally, neither initial (within 45 min postmortem) nor ultimate (24 to 48 h postmortem) LM pH has been shown to be altered by feeding diets formulated with pork fat (Scheeder et al., 2000), beef tallow (Engel et al., 2001; Corino et al., 2002), poultry fat (Engel et al., 2001), SBO (Scheeder et al., 2000), corn oil (Corino et al., 2002), canola oil (Corino et al., 2002), and olive oil (Scheeder et al., 2000).

Drip loss percentages were not altered by either dietary RAC inclusion (P = 0.14) or fat source (P = 0.57; Table 4). Even though Carr et al. (2005a) reported that feeding pigs diets formulated with 20 mg/kg of RAC reduced LM drip loss percentages, most research has failed to observe an effect of RAC (Stoller et al., 2003; Carr et al., 2005b; Weber et al., 2006) or dietary fat source (Engel et al., 2001; Corino et al., 2002; Weber et al., 2006) on the water-holding capacity of the LM.

Fatty Acid Composition of Pork Backfat

Including 10 mg/kg of RAC in swine finishing diets reduced (P < 0.01) the proportions of all SFA, as well as palmitic acid, by 3.4 and 4.0%, respectively (Table 5). As expected, backfat samples from BT-fed pigs had greater (P 0.03) percentages of total SFA, as well as myristic and palmitic acids. Regardless of dietary RAC inclusion, backfat from pigs fed BT had greater (P < 0.05) proportions of stearic acid than backfat from SBO-fed pigs; however, inclusion of RAC in diets formulated with SBO further reduced (P < 0.05) stearic acid levels compared with SBO-diets devoid of RAC (RAC x dietary fat source, P = 0.04; Figure 1).

View larger version (30K): [in this window] [in a new window]   Figure 1. The interactive effect of dietary ractopamine (0 vs. 10 mg/kg) and fat source (soybean oil vs. beef tallow) on the weight percentage of stearic acid in pork backfat samples (ractopamine x fat source, P = 0.04). x–zBars lacking a common letter differ, P < 0.05.

Compared with untreated controls, dietary inclusion of RAC reduced (P = 0.04) total MUFA percentages by only 2.6%, with the greatest reduction observed in the proportion of oleic acid (P < 0.01; Table 5). However, research has indicated that MUFA concentrations of pork s.c. fat were not altered by feeding either 10 (Carr et al., 2005b; Xi et al., 2005; Weber et al., 2006) or 20 mg/kg of RAC (Engeseth et al., 1992; Perkins et al., 1992).

Backfat samples from BT-fed pigs had substantially greater (P < 0.01) proportions of all MUFA than samples from SBO-fed pigs (Table 5). Myristoleic acid was only detected (P < 0.01) in backfat from BT-fed pigs, and palmitelaidic, palmitoleic, all 18:1 trans fatty acids, oleic, vaccenic, and gadoleic acids were increased (P < 0.01) by 137.7, 31.0, 38.7, 11.5, 9.4, and 17.7%, respectively, by including 5% BT in the diet. When comparing diets formulated with choice white grease and BT to diets with no added fat, Weber et al. (2006) reported that MUFA concentrations were greater in the inner and outer backfat layers of pigs fed the animal fat sources. Additionally, feeding BT has been shown to increase the proportion of oleic acid in backfat samples when compared with feeding corn oil (Kouba and Mourot, 1999), safflower oil (Larick et al., 1992), or whole, crushed linseed (Kouba et al., 2003). However, Klingenberg et al. (1995) reported that feeding 10% high-oleic sunflower oil increased the weight percentage of oleic acid in pork backfat compared with backfat from pigs fed 10% BT. Miller et al. (1990) also reported that feeding diets formulated with 10% sunflower oil produced the lowest backfat MUFA concentrations, especially when compared with backfat samples from pigs fed diets formulated with animal fat or canola oil.

It is not surprising that the total proportion of PUFA was increased (P < 0.01) in the backfat of SBO-fed pigs compared with BT-fed pigs (Table 5). In particular, feeding diets formulated with SBO elevated (P < 0.01) the percentages of linoleic, -linolenic, eicosadienoic, eicosatrienoic, and arachidonic acids in backfat by 46.2, 128.6, 41.4, 118.9, and 23.2%, respectively, over that from BT-fed pigs. Yet, feeding BT-supplemented diets increased (P < 0.01) the proportion of CLA in the backfat by over 46% compared with samples from SBO-fed pigs.

Research has demonstrated that concentrations of linoleic and linolenic acids increased with increasing time pigs were fed diets formulated with full-fat soybeans (Warnants et al., 1999), increased dietary levels of canola oil (St. John et al., 1987), and increased dietary IV (Gatlin et al., 2003). Backfat from pigs fed diets formulated with corn oil (Kouba and Mourot, 1999; King et al., 2004) or safflower oil (Larick et al., 1992) had a greater percentage of linoleic acid than backfat from pigs fed diets formulated with BT. Conversely, Miller et al. (1990) reported that backfat from pigs fed 10% sunflower oil had the greatest, whereas backfat from pigs fed 10% animal fat had the lowest, concentrations of SFA; however, Klingenberg et al. (1995) failed to detect changes in the backfat weight percentages of linoleic and linolenic acids between pigs fed 10% sunflower oil or 10% BT.

The proportion of all PUFA in the backfat was increased (P < 0.01) by almost 1.1 percentage units by including RAC in the finishing diet (Table 5). More specifically, inclusion of RAC increased (P 0.04) the concentrations of linoleic, -linolenic, eicosadienoic, and arachidonic acids by 9.6, 11.8, 5.9, and 10.9%, respectively, above the concentrations detected in back-fat samples from untreated controls.

Perkins et al. (1992) reported that the PUFA content increased 10.2, 7.3, and 9.5% by feeding 5, 10, and 20 mg/kg of RAC, respectively, and Engeseth et al. (1992) found that the proportions of linoleic and linolenic acids increased in subcutaneous fat samples. Moreover, Xi et al. (2005) showed that PUFA concentrations were similar in backfat samples from pigs fed 0 and 5 mg/kg of RAC; however, the PUFA content of backfat from pigs fed 10 mg/kg of RAC was reduced 8.3% compared with backfat from pigs fed 0 and 5 mg/kg of RAC. Carr et al. (2005b) and Weber et al. (2006) demonstrated that feeding diets formulated with 10 mg/kg of RAC increased the proportion of PUFA in backfat samples. The increased polyunsaturation of backfat from RAC-fed pigs was primarily a result of greater proportions of absorbed linoleic acid (Carr et al., 2005b; Xi et al., 2005; Weber et al., 2006) and -linolenic acid (Engeseth et al., 1992).

Pigs fed BT-diets had a greater (P < 0.01) proportion of unidentified fatty acid peaks, but the proportion of other (unidentified) fatty acids did not differ (P = 0.10) between pigs fed 0 or 10 mg/kg of RAC (Table 5). The percentages of n-3 and n-6 fatty acids were elevated (P < 0.01) in backfat samples from RAC-fed pigs, as well as in backfat of SBO-fed pigs, but there were no RAC x dietary fat interactions (P 0.16). Interestingly, the n-6:n-3 was substantially reduced (P < 0.01) by feeding diets formulated with SBO, but not with RAC (P = 0.27). The PUFA:SFA ratio and IV of backfat from RAC-fed pigs were 0.09 and 2.78 units greater (P < 0.01) than that from pigs fed the control diet, whereas the PUFA:SFA and IV were elevated (P < 0.01) 0.34 and 11.48 units by including SBO in the finishing diet.

Kouba et al. (2003) and Leskanich et al. (1997) reported that the n-6:n-3 was greater, but the PUFA:SFA less, in backfat from pigs fed a BT/SBO blend compared with backfat from pigs fed whole, crushed linseed and a canola oil/fish oil blend, respectively. Furthermore, increasing the IV of the swine diet would obviously cause an increase in the IV of s.c. fat (Gatlin et al., 2003). Yet, even though Xi et al. (2005) reported corresponding increases in PUFA concentrations and IV in backfat from pigs fed 10 mg/kg or RAC, neither Weber et al. (2006) nor Carr et al. (2005b) observed a significant change in backfat IV in response to feeding diets formulated with 10 mg/kg of RAC. More importantly, the IV of back-fat from RAC-fed pigs was below, or equal to, 70 mg of I/100 mg of fat, indicating that the fat from pigs fed RAC was of high quality (Lea et al., 1970).

LM Quality During Simulated Retail Display

There were no RAC x display day (P 0.71) dietary fat source x display day (P 0.21), or RAC x dietary fat source x display day (P 0.26) interactions; therefore, only the main effects of RAC and dietary fat source are presented in Table 6. Across the 5 d of simulated retail display, LM chops from pigs fed RAC received greater (P 0.01) subjective color scores, as well as greater (P < 0.01) marbling scores, than chops from pigs fed the control diet. These results are in contrast to several studies demonstrating that neither Japanese (Carr et al., 2005a, b; Armstrong et al., 2004) nor American (Stoller et al., 2003; Carr et al., 2005a, b) color scores were affected when swine diets were formulated with 10 mg/kg of RAC. Except for the results of Aalhus et al. (1990), which implied that feeding 20 mg/kg of RAC reduced LM marbling scores, research has shown that feeding diets formulated with RAC has little to no impact on LM marbling scores (Carr et al., 2005a, b; Weber et al., 2006) or extracted lipid content (Stoller et al., 2003; Carr et al., 2005b; Weber et al., 2006).

Chops from pigs fed the diet formulated with SBO received greater (P < 0.01) Japanese and American color scores than chops from BT-fed pigs; however, chops from pigs fed 5% BT received greater (P < 0.01) marbling scores than chops from SBO-fed pigs (Table 6). Additionally, chops from SBO-fed pigs were darker (P < 0.01) and redder (higher a* value and lower hue angle; P < 0.01) than chops originating from pigs fed the BT-diet.

Miller et al. (1990) reported that feeding pigs diets formulated with 10% sunflower oil produced paler colored pork; however, LM color and marbling scores were not affected by feeding animal fats (Nichols et al., 1991; Engel et al., 2001; Weber et al., 2006) or seed oils other than SBO (Miller et al., 1990; Nichols et al., 1991). In contrast to results of this study, however, LM L*, a*, and b* values were not different between LM chops from pigs fed beef tallow (Corino et al., 2002), choice white grease (Engel et al., 2001), pork fat (Scheeder et al., 2000), poultry fat (Engel et al., 2001), or any number of oil seeds (Scheeder et al., 2000; Corino et al., 2002). Interestingly, LM chops from pigs fed 2% sunflower oil were darker (lower L* values) than chops from pigs fed 2% olive oil or a combination of sunflower and linseed oil after 6 d of retail display, and chops from pigs fed olive oil remained redder after 9 d of retail display than chops from pigs fed the sunflower/linseed oil blend (Rey et al., 2001).

As expected, TBARS values increased (P < 0.01) over the 5 d of simulated retail display (0.25 vs. 0.52 mg of maldenaldehyde/kg of fresh tissue; results not presented); however, neither dietary RAC inclusion (P = 0.58) nor dietary fat source (P = 0.47) altered TBARS values during the 5 d of simulated retail display (Table 6). Although there are no reports on the effects of RAC on lipid oxidation, it could easily be hypothesized that the increase in PUFA would reduce the oxidative stability of i.m. lipids, resulting in development of lipid oxidative products (Wood et al., 2003). Moreover, Corino et al. (2002) reported that LM chops from pigs fed BT had lower TBARS values than chops from pigs fed corn oil or canola oil after 5 h of induced oxidation. Yet, West and Myer (1987) reported that the linoleic acid concentration in backfat was increased approximately 164% by feeding pigs peanuts, but the extent of fatty acid oxidation in LM chops of peanut-fed pigs was similar to that of chops from pigs fed the control diet after 4 mo of vacuum-packaged frozen storage. Thus, elevations in the proportions of linoleic and linolenic acids in back-fat samples from RAC-fed and SBO-fed pigs were not indicative of changes in i.m. fatty acid composition or lipid oxidative stability.

Warner-Bratzler Shear Force Determinations

Longissimus muscle cooking losses and WBSF values were not affected by dietary RAC (P 0.13) or fat source (P 0.32), nor were there RAC x dietary fat source interactions (P 0.11) for cooking loss percentages and WBSF values (Table 6). Additionally, there were no (P 0.17) interactions with display duration; however, aging LM chops an additional 7 d effectively lowered (P < 0.01) cooking losses (26.6 vs. 24.3%) and WBSF (3.98 vs. 3.62 kg) values (results not presented).

Pork from pigs consuming diets formulated with 10 mg/kg of RAC had similar cooking loss percentages to pork from pigs fed untreated diets (Stoller et al., 2003; Carr et al., 2005a, b), whereas cooking losses were not altered by feeding diets formulated with animal fats (Leskanich et al., 1997; Scheeder et al., 2000; Corino et al., 2002), SBO (Scheeder et al., 2000), corn oil (Corino et al., 2002), canola oil (Miller et al., 1990; Leskanich et al., 1997; Corino et al., 2002), or safflower and sunflower oils (Miller et al., 1990). Additionally, WBSF results of this study are consistent with results of Stoller et al. (2003) and Smith et al. (1995), who failed to detect an effect of RAC on WBSF values. It should be noted, however, that Carr et al. (2005a, b) demonstrated that feeding diets formulated with 10 mg/kg of RAC increased WBSF values compared with chops from pigs fed the control diet. Similarly, Kouba et al. (2003) reported that chops from pigs fed 6% linseed oil had greater WBSF values than chops from pigs fed 4% of a BT/SBO blend, and Leskanich et al. (1997) reported that chops from pigs fed 3% of a BT/SBO blend were rated tougher than chops from pigs fed 2% canola oil/1% fish oil. However, the majority of the literature indicates that cooked pork tenderness is not affected by including an animal or vegetable fat source, or both, to swine finishing diets.

As expected, formulating finishing diets with 5% soybean oil instead of beef tallow resulted in increased polyunsaturation of pork backfat, subsequently increasing the iodine value. Conversely, feeding finishing swine ractopamine during the last 35 d before slaughter may increase the degree of polyunsaturation of pork backfat, but the backfat iodine value was well within an acceptable range. As expected, the inclusion of ractopamine in the late-finishing diet improved live performance and carcass leanness, whereas LM quality was either not altered or actually enhanced during 5 d of retail display by feeding 10 mg/kg of ractopamine.

	Footnotes

 
¹ The authors express their appreciation to Elanco Animal Health, a division of Eli Lilly and Company, for financial support of this experiment, and Tyson Foods Inc. (Springdale, AR) for donation of beef tallow. Additionally, the authors gratefully acknowledge the assistance of K. Richardson and employees at Sara Lee (West Point, MS) with pig slaughter, carcass fabrication, and subprimal cut procurement; A. Hays and M. E. Davis for animal care and performance data collection; and J. Stephenson for assistance with pork loin fabrication/processing and data collection.

² Corresponding author: japple{at}uark.edu

Received for publication June 4, 2007. Accepted for publication May 8, 2008.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION LITERATURE CITED

 


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