J. Anim Sci. 2007. 85:737-745. doi:10.2527/jas.2006-231
© 2007 American Society of Animal Science
Effect of supplemental iron on finishing swine performance, carcass characteristics, and pork quality during retail display1
J. K. Apple*,2,
W. A. Wallis-Phelps*,3,
C. V. Maxwell*,
L. K. Rakes*,
J. T. Sawyer*,
S. Hutchison*,4 and
T. M. Fakler
* Department of Animal Science, University of Arkansas, Fayetteville 72701; and
and
Zinpro Corporation, Eden Prairie, MN 55334
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Abstract
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Crossbred pigs (n = 185) were used to test the effects of dietary Fe supplementation on performance and carcass characteristics of growing-finishing swine. Pigs were blocked by BW, allotted to pens (5 to 6 pigs/pen), and pens (5 pens/block) were allotted randomly to either negative control (NC) corn-soybean meal grower and finisher diets devoid of Fe in the mineral premix, positive control (PC) corn-soybean meal grower and finisher diets with Fe included in the mineral premix, or the PC diets supplemented with 50, 100, or 150 ppm Fe from Availa-Fe (an Fe-AA complex). When the lightest block averaged 118.2 kg, the pigs were slaughtered, and bone-in pork loins were collected during fabrication for pork quality data. During the grower-I phase, there was a tendency for supplemental Fe to reduce ADG linearly (P = 0.10), whereas in the grower-II phase, supplemental Fe tended to increase ADG linearly (P = 0.10). Even though pigs fed NC had greater G:F during the finisher-I phase (P < 0.05) and across the entire trial (P = 0.07), live performance did not (P 
0.13) differ among dietary treatments. There were linear increases in 10th-rib fat depth (P = 0.08) and calculated fat-free lean yield (P = 0.06); otherwise, dietary Fe did not (P > 0.19) affect pork carcass muscling or fatness. Moreover, LM concentrations of total, heme, and nonheme Fe were similar (P > 0.23) among treatments. A randomly selected subset of loins from each treatment was further fabricated into 2.5-cm-thick LM chops, placed on styrofoam trays, overwrapped with polyvinyl chloride film, and placed in coffin-chest display cases (2.6°C) under continuous fluorescent lighting (1,600 lx) for 7 d. During display, chops from NC-fed pigs and pigs fed the diets supplemented with 100 ppm Fe tended to have a more vivid (higher chroma value; P = 0.07), redder (higher a* value; P = 0.09) color than LM chops of pigs fed 50 ppm of supplemental Fe. Moreover, greater (P < 0.01) redness:yellowness ratios in chops from pigs supplemented with 100 ppm Fe indicated a more red color than chops from PC-fed pigs or pigs fed diets supplemented with 50 ppm Fe. In conclusion, however, increasing dietary Fe had no appreciable effects on performance, carcass, or LM characteristics, suggesting that current dietary Fe recommendations are sufficient for optimal growth performance, pork carcass composition, and pork quality.
Key Words: carcass composition • growth • iron • meat quality • pork • retail display
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INTRODUCTION
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It is common practice to supply the newborn pig with Fe via i.m. injections of 100 to 200 mg; however, post-weaning Fe requirements are approximately 80 ppm (Pickett et al., 1960
) and decline with advancing age and BW (National Research Council, 1998). Harmon et al. (1969) reported that ADG was reduced with swine diets containing less than 29 ppm Fe, but ADG was not altered at dietary levels ranging from 34 to 117 ppm. Also, supplementing swine diets with 100 to 1,000 ppm Fe failed to affect live pig performance (Dove and Ewan, 1990). Interestingly, none of the aforementioned studies evaluated the effects of dietary Fe on pork carcass composition or quality.
Myoglobin, a heme protein, is the primary pigment in meat, and dietary Fe supplementation has been shown to increase levels of total and heme Fe (Yu et al., 2000), but not muscle nonheme Fe levels (Miller et al., 1994b; Yu et al., 2000) in pork. Although increasing dietary Fe in calf (Abdelrahim et al., 1983) and swine diets (Yu et al., 2000) produces darker veal and redder pigskin, respectively, O’Sullivan et al. (2002) reported that feeding 3,000 ppm of FeSO4 resulted in greater discoloration during retail display, attributed to increased metmyoglobin formation. Furthermore, Miller et al. (1994a, b) observed that supplementing swine diets with FeSO4 increased lipid peroxidation in cooked ground pork and pork chops, but not in fresh, whole-muscle pork, stored for up to 12 wk. Conversely, there is no available information concerning the effects of supplementing swine diets with an organic Fe source, like Availa-Fe (Fe-AA complex produced by Zinpro Corp.), on quality and shelf life of fresh pork.
Therefore, the objectives of this study were to test the effect of supplementing diets of growing-finishing swine with Availa-Fe on the following: 1) live pig performance, 2) pork carcass composition and quality, and 3) fresh pork color and lipid oxidation during 7 d of retail display.
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MATERIALS AND METHODS
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Animals and Diets
The University of Arkansas Interdepartmental Animal Care and Use Committee approved animal care, as well as all experimental procedures and protocols involving animals, before initiation of this trial.
One hundred eighty-five crossbred pigs (90 barrows and 95 gilts), from the mating of EB boars to line 348 females (Monsanto Choice Genetics, St. Louis, MO), were blocked by BW (30.4 ± 4.6 kg) into 7 blocks and allocated randomly within blocks to pens (6 pigs/pen in blocks 1 and 2 and 5 pigs/pen in blocks 3, 4, 5, 6, and 7), with stratification across pens based on sex and litter origin. Within blocks, pens were randomly assigned to 1 of 5 dietary treatments (as-fed basis): negative control (NC) corn-soybean meal grower and finisher diets with no Fe included in the mineral premix, positive control (PC) corn-soybean meal grower and finisher diets with Fe from FeSO4 included in the mineral premix, or PC diets supplemented with 50, 100, or 150 ppm Fe from Availa-Fe, an Fe-AA complex.
Pigs were fed a 4-phase dietary program, with the transition from grower-I to grower-II, grower-II to finisher-I, and finisher-I to finisher-II at average block BW of 54.5, 68.2, and 90.9 kg, respectively. Experimental diets (Table 1) were formulated to be isolysinic (lysine content of grower-I, grower-II, finisher-I, and finisher-II phases was 1.00, 0.86, 0.72, and 0.64%, respectively, as-fed basis) and isocaloric (ME content of grower-I, grower-II, finisher-I, and finisher-II phases was 3.42, 3.46, 3.47, and 3.45 Mcal/kg, respectively, as-fed basis). Two mineral premixes were produced: one supplying 100 ppm Fe from FeSO4 per kilogram of feed (PC diets), whereas the other premix was devoid of FeSO4 (NC diets). Also, Availa-Fe was included in the diets at the expense of corn (Table 1), and all diets were formulated to meet or exceed National Research Council (1998) requirements for growing-finishing swine.
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Table 1. Composition of negative control (NC) and positive control (PC) grower-I, grower-II, finisher-I, and finisher-II diets
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Pigs were housed in a curtain-sided building with completely slatted concrete floors, and each pen was 1.52 x 3.05, affording at least 0.77 m2 of space per pig. Each pen was equipped with a single-opening feeder and cup waterers. Pigs were weighed and feed disappearance was recorded weekly during each feeding phase to calculate ADG, ADFI, and G:F on an as-fed basis.
Carcass Data Collection
When the lightest block of pigs averaged 118.2 kg of BW, all pigs were transported approximately 8 h (760 km) to a commercial pork packing plant (Bryan Foods Inc., West Point, MS) and slaughtered after a 12-h rest period (with ad libitum access to water) at the plant. Tenth-rib fat and LM depths were measured online with a Fat-O-Meater (FOM) automated probe (SFK Technology A/S, Cedar Rapids, IA) inserted between the 10th and 11th ribs at a distance of approximately 7 cm from the midline, and HCW and FOM-estimated fat-free lean yield were recorded. Then, carcasses were subjected to a conventional spray-chilling system for 24 h. Before carcass fabrication, loins were identified, and the vertebral column was marked between the 10th and 11th ribs to measure LM area upon arrival at the University of Arkansas Red Meat Abattoir. During carcass fabrication, bone-in pork loins (IMPS no. 410) were captured, vacuum-packaged, boxed, loaded onto a refrigerated truck, and transported to the University of Arkansas for pork quality data collection.
At approximately 48 h postmortem, all pork loins were cut at the mark between the 10th and 11th ribs, and the area of the LM was traced onto acetate paper for measurement of LM using a compensating planimeter. Two 3.8-cm-thick LM chops were cut cranial to the 10th rib to measure drip loss percentage according to the suspension procedure of Honikel et al. (1986), with modifications described by Apple et al. (2000). After core removal for the drip loss procedure, approximately 2 g of LM was homogenized in 20 mL of distilled, deionized water, and the pH of the homogenate was measured with a temperature-compensating combination electrode (300731.1; Denver Instrument Co., Arvada, CO) attached to a pH/ion/FET meter (AP25; Denver Instrument Co.). Remaining portions of the LM were subsequently vacuum-packaged and frozen at –20°C for moisture and Fe (total, heme, and nonheme Fe) analyses.
Two 2.5-cm-thick LM chops were removed caudal to the 11th rib from all loins, and, after a 45-min bloom time at 2°C, were visually evaluated by 3 trained university personnel for marbling (1 = 1% i.m. fat to 10 = 10% i.m. fat; National Pork Producers Council, 1999), firmness and wetness (1 = very soft and watery to 5 = very firm and dry; National Pork Producers Council, 1991), and color based on both the American (1 = pale, pinkish gray to 6 = dark, purplish red; National Pork Producers Council, 1999) and Japanese (Nakai et al., 1975) color standards. After visual appraisal, the chops were wrapped in freezer paper; 1 randomly selected chop was immediately frozen at –20°C, whereas the other chop was aged an additional 7 d at 4°C and frozen at –20°C before cooking loss and Warner-Bratzler shear force determinations were conducted according to procedures outlined by Apple et al. (2000).
Retail Display
Because of limited space in the retail display case, a subsample of pork loins was randomly selected before loin fabrication from each dietary treatment group (n = 20/treatment), with the goal of at least 2 loins from each pen. From the selected loins, an additional four 2.5-cm-thick LM chops (removed from the caudal portion of the loin) were weighed, placed on styrofoam trays (with an absorbent pad), and overwrapped with O2-permeable polyvinyl chloride film [O2 transmission rate = 14,000 mL/(m2·24 h) at 1 atmosphere; Borden Inc., Dallas, TX]. Subsequently, packaged chops were randomly assigned to 1 of 4 retail display durations (0, 1, 4, or 7 d) and 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, 4, and 7 of retail display, lightness (L*), redness (a*), and yellowness (b*) values, as well as reflectance values in the visible spectrum from 580 to 630 nm, 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*). Chroma, or saturation index (representing the total color, or vividness, of the LM), was calculated as: 
. The change in total color (
E) from d 0 LM chops was calculated as: 
(Minolta, 1998). Additionally, the a*:b* ratio (another measure of LM redness) and the reflectance ratio of 630 nm:580 nm (used to estimate the oxymyoglobin proportion; Hunt et al., 1991) were determined on d 0, 1, 4, and 7 of retail display.
After objective color data collection on d 1, 4, and 7 of retail display, chops were removed from the packages, blotted dry on paper towels, and reweighed. The difference between the respective display-day and initial weights was divided by the initial weight to calculate moisture loss percentage. Also, on d 0, 1, 4, and 7 of retail display, approximately 10 g of LM was removed, pulverized in liquid N using a Waring blender (38BL54, Waring Commercial, New Hartford, CT), placed in Whirl-Pak bags (Nasco, Fort Atkinson, WI), and frozen at –20°C before assaying for 2-thiobarbituric acid reactive substances (TBARS) in accordance with the procedure of Witte et al. (1970), with modifications described by Apple et al. (2001).
Moisture and Fe Content of LM
Moisture content of the LM was measured using the freeze-drying method of Apple et al. (2001). Total Fe and nonheme Fe concentrations were determined on triplicate LM samples using the procedure of Schricker et al. (1982), as modified by Rhee and Ziprin (1987). The difference between total and nonheme Fe concentrations was used as a measure of heme Fe concentrations.
Statistical Analyses
Data were analyzed as a randomized complete block design, with blocks based on initial BW, using the MIXED procedure (SAS Inst. Inc., Cary, NC). The experimental unit for all performance, carcass composition, and initial pork quality data was pen of pigs. In the ANOVA of performance, carcass composition, LM Fe concentrations, and initial pork carcass quality data, dietary treatment was the lone fixed effect and block was the random effect included in the model. Least squares means were computed for the dietary treatments and statistically separated using pairwise t-tests (PDIFF option of SAS) when a significant (P < 0.05) F-test was detected. Additionally, preplanned orthogonal contrasts were used to accurately compare NC and PC diets as well as linear and quadratic responses to dietary inclusion level (PC, 50, 100, and 150 ppm).
Pork quality data collected during retail display were analyzed as repeated measures using the MIVQUE(0) option of PROC MIXED, with display day as the repeated variable and pork loin as the subject. Because of mislabeling, 1 pen within a dietary treatment was not represented by 2 loins, and complete retail display data (d 0, 1, 4, and 7) were collected for only 18, 16, 16, 14, and 19 loins from carcasses of pigs fed NC, PC, and PC diets supplemented with 50, 100, and 150 ppm Fe, respectively; therefore, the experimental unit for the ANOVA of the display data was individual loin. Fixed (main) effects included in the model were dietary treatment and display day, as well as the 2-way interaction, whereas block and block x pen x dietary treatment were included in the model as random effects. Least squares means were computed for the main effects and their interaction and were separated statistically using F-protected (P < 0.05) t-tests (PDIFF option).
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RESULTS AND DISCUSSION
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Live Pig Performance
Dietary treatment effects on live pig performance are presented in Table 2. During the grower-I phase, ADG tended to decrease linearly (P = 0.10) as supplemental Fe increased in the PC diets, whereas, during the grower-II phase, there was a tendency for a linear increase (P = 0.10) in ADG among Fe-fed pigs. Conversely, neither ADFI nor G:F were affected (P 0.14) by any dietary treatment during the grower phases. Even though ADG and ADFI were not (P 0.15) altered by feeding diets supplemented with Fe during the early-finisher phase, pigs fed the NC diet were more (P < 0.05) efficient than their PC-fed counterparts. Neither diet nor Fe supplementation level affected (P 0.13) performance during the late-finisher phase, and, with the exception that NC-fed pigs tended to have higher (P = 0.07) G:F, overall performance did not (P 0.19) differ among dietary treatments.
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Table 2. Effects of the dietary inclusion level (50, 100, or 150 ppm) of Fe from Availa-Fe on growth performance of growing-finishing swine
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The pig is born with approximately 50 mg of Fe, most of which is as hemoglobin (Miller et al., 1961), and the Fe content of sow’s milk is low, approximately 1.5 mg/ L (Spruill et al., 1971). Therefore, pigs receiving only milk rapidly become anemic, and it is common practice in swine production to supply the newborn pig with Fe. Intramuscular injections of 100 to 200 mg of Fe have been shown to improve BW gain of nursing pigs compared with untreated pigs (Danielson and Noonan, 1975; Pollmann et al., 1983; Hill et al., 1999), but daily oral supplementations of 10 or 40 ppm Fe do not affect BW gain of nursing pigs (Furugouri, 1972a). Ammerman et al. (1974) found that supplementing nursery diets with 40 ppm Fe from FeSO4 improved ADG, but not ADFI or feed efficiency, over unsupplemented controls or diets supplemented with FeCO3, whereas Rincker et al. (2004) observed a linear increase in ADG as supplemental Fe increased from 0 to 150 ppm in nursery diets. On the other hand, Dove and Haydon (1991) failed to detect an effect of supplementing 50 to 300 ppm Fe on live pig performance, nor was performance altered in 60-d-old pigs supplemented with 3,102 ppm Fe (Furugouri, 1972b). It should be noted, however, that supplementing swine with 5,102 ppm Fe from FeSO4 adversely affects pig performance by interfering with P absorption (Furugouri, 1972b).
Prince et al. (1979) reported a quadratic reduction in ADG during the growing phase as the level of FeSO4 was increased in the diet, but overall ADG and feed efficiency were not affected by level of dietary Fe (Prince et al., 1979; Ribeiro de Lima et al., 1981). Similar to results of this study, finishing pig performance is not altered at dietary Fe levels ranging from 34 to 1,000 ppm (Harmon et al., 1969; Hedges and Kornegay, 1973; Dove and Ewan, 1990). Additionally, neither ADG, ADFI, nor feed efficiency is affected by supplementing swine diets with from 30 to 120 ppm Fe from Availa-Fe (Yu et al., 2000; Saddoris et al., 2003). In accordance with the literature, results of this study indicate that current National Research Council (1998) Fe requirements are sufficient for optimal performance of growing-finishing swine, and there is no benefit of supplementing diets with additional Fe on live pig performance.
Carcass Composition and Quality
Slaughter and HCW, as well as dressing percentage, fat depth, LM depth and area, and FOM-estimated fat-free lean yield, were similar (P 0.14) between carcasses of pigs fed NC or PC diets (Table 3). Even though there was a tendency for 10th-rib fat depth to increase (P = 0.08) and fat-free lean yield (P = 0.06) to decrease linearly as dietary Fe increased from 50 to 150 ppm, supplementing swine diets with Fe levels greater than National Research Council (1998) requirements did not (P 0.32) alter carcass muscling or fatness.
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Table 3. Effects of the dietary inclusion level (50, 100, or 150 ppm) of Fe from Availa-Fe on pork carcass composition
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Very little information is available concerning the effects of dietary Fe on pork carcass composition or pork quality. Saddoris et al. (2003) observed that supplementing swine diets with 90 ppm Fe from either Availa- Fe or FeSO4 did not affect average backfat depth or LM area, whereas Field et al. (1985) reported that kidney fat weight and s.c. fat depth measurements were increased in lamb carcasses from sheep intraruminally intubated with solutions containing 250 mg of Fe (from FeO) per kilogram of BW. Additionally, Lapierre et al. (1990) indicated that dressing percentage was not affected by feeding veal calves 100, 150, or 200 ppm Fe.
Even though there was a linear (P = 0.10) trend for ultimate (48-h) pH to increase in the LM of pigs fed Fe-supplemented diets, subjective color, marbling, and firmness scores did not (P 0.21) differ among dietary treatments (Table 4). Supplementing swine diets with Fe had no (P 0.21) effect on LM moisture content or drip loss percentage. Saddoris et al. (2003) reported that pork pH, as well as subjective color, firmness, and marbling scores, were similar among pigs fed a control diet or diets supplemented with 90 ppm Fe. Field et al. (1985) found that ultimate muscle pH was not affected by treating sheep with a solution containing 250 mg of Fe, and Gariépy et al. (1998) found that ultimate muscle pH was not affected by feeding calves diets varying in Fe content. Additionally, drip loss percentages are not altered in the LM from pigs (O’Sullivan et al., 2002) or veal calves (Gariépy et al., 1998) by increasing dietary Fe levels, which is in agreement with results of the current study.
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Table 4. Effects of the dietary inclusion level (50, 100, or 150 ppm) of Fe from Availa-Fe on initial pork quality and LM Fe characteristics
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In contrast to previous studies with pigs (Yu et al., 2000; O’Sullivan et al., 2002, 2003b), supplementing swine diets with Fe did not (P 0.23) alter LM total, heme, and nonheme Fe concentrations. Miller et al. (1994a) observed that nonheme Fe concentrations of fresh LM and rectus femoris were similar among pigs fed diets containing 62, 131, and 209 ppm Fe. Moreover, neither treating sheep with FeO (Field et al., 1985) nor supplementing veal calf diets with Fe (Lapierre et al., 1990) affected total muscle Fe content. It should be noted that the elevated total LM Fe concentrations reported by O’Sullivan et al. (2002, 2003b) were in response to supplementing swine finishing diets with 3,000 ppm Fe from FeSO4.
Pork Quality During Retail Display
As expected, moisture loss percentage, L*, a*, and b* values increased with increasing days in retail display (results not shown). Chops from pigs fed diets supplemented with 50 ppm Fe had lower (P < 0.05) moisture loss percentages across the 7 d of retail display than those from pigs fed the NC and PC diets, as well as pigs fed diets supplemented with 150 ppm Fe (Table 5). Neither L* (P = 0.92) nor b* (P = 0.13) values were affected by the dietary treatments; however, chops from pigs fed the NC diets or diets supplemented with 100 ppm Fe tended to be redder (higher a* values; P = 0.09) than chops from pigs fed diets supplemented with 50 ppm Fe. Even though LM hue angles (P = 0.12) and estimated oxymyoglobin content (R630:R580 nm; P = 0.79) were similar among dietary treatments during retail display, LM chops from pigs fed an additional 100 ppm Fe had greater a*:b* (P < 0.01) and chroma values (P = 0.07)—indicating a redder, more vivid color—than chops from pigs fed the PC diets or diets supplemented with 50 ppm Fe.
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Table 5. Main effects of the dietary inclusion level (50, 100, or 150 ppm) of Fe from Availa-Fe on LM quality across the 7 d of retail display
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Supplementing swine diets with 90 ppm of Fe from Availa-Fe results in a redder (higher a* values) LM after 1, 3, 5, and 7 d of simulated retail display compared with pigs fed the control diet or a diet supplemented with 90 ppm Fe from FeSO4 (Saddoris et al., 2003). Furthermore, increasing dietary Fe in calf diets produces darker, redder veal than unsupplemented diets (Abdelrahim et al., 1983; Lapierre et al., 1990); specifically, Gariépy et al. (1998) reported that L* values were lower and a* values higher in veal from calves fed grain-based diets containing 77 to 217 ppm Fe than calves fed a milk diet containing from 4 to 45 ppm Fe. The increased a* values of postmortem muscle may be a result of accumulation of myoglobin (Hagler et al., 1981; Beauchemin et al., 1990) in response to dietary Fe level.
After 1 d of retail display, LM chops from pigs fed the NC diets and diets supplemented with 150 ppm Fe had lower E values (indicating less change in color from d 0 chops) than pigs fed diets supplemented with 50 ppm Fe (dietary treatment x display day, P = 0.041; Figure 1). Yet, after 4 d in display, the color of chops from pigs fed an additional 50 ppm Fe had changed less (P < 0.05) than chops from NC- and PC-fed pigs, but, by d 7 of display, LM E values were similar among dietary treatments.
Although TBARS values were low during retail display (increasing from 0.08 to 0.16 mg/kg from d 0 to 7; results not shown), there was a dietary treatment x display day interaction (P = 0.012) on TBARS values (Figure 2). On d 0 of display, LM chops from NC-fed pigs had lower (P < 0.05) TBARS values than chops from pigs fed the PC diets or diets supplemented with 150 ppm Fe. There were no differences in TBARS values on d 1, but chops from pigs fed diets supplemented with 150 ppm Fe had lower (P < 0.05) TBARS values than all other dietary treatments after 4 d of retail display, and, after 7 d of retail display, chops from pigs fed diets fortified with 100 ppm Fe had lower (P < 0.05) TBARS values than chops from pigs fed PC diets with an additional 50 ppm Fe.
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Figure 2. The effects of dietary Fe supplementation on 2-thiobarbituric acid reactive substances (TBARS) values during 7 d of retail display (treatment x display time, P = 0.012). Within a specific display time, bars lacking common letters differ (P < 0.05). NC = negative control diet with no Fe included in the mineral premix; PC = positive control diet with 100 ppm Fe from FeSO4 included in the mineral premix.
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Although little is known about the effects of dietary Fe on pork quality during retail display, O’Sullivan et al. (2002) demonstrated that feeding 3,000 ppm Fe resulted in greater discoloration of LM chops during 5 d of retail display, which was attributed to increased metmyoglobin formation. Moreover, TBARS values are elevated in cooked LM chops (Miller et al., 1994a) and ground pork patties (Miller et al., 1994b) by feeding 131 and 209 ppm Fe, even though dietary Fe has no detrimental effects on fresh pork TBARS values. O’Sullivan et al. (2003a) reported that warmed-over flavor was increased in chops from pigs fed 3,000 ppm Fe, indicating increased lipid oxidation. This is not surprising, because lipid and pigment oxidation are closely coupled—an increase in one typically results in a similar increase in the other (Faustman and Cassens, 1990). Faustman et al. (1992) found that total Fe and nonheme Fe concentrations were significantly correlated with metmyoglobin formation, and metmyoglobin (Tichivangana and Morrissey, 1985), heme (Kanner et al., 1988), and nonheme (Igene et al., 1979) Fe catalyze lipid oxidation in fresh and cooked meats. However, feeding 100 ppm Fe from Availa-Fe reduced the amount of total color change (lower E values), whereas supplementing swine diets with 150 ppm Fe actually reduced TBARS values, after 4 d of retail display. Thus, results of the current study would indicate that the supplementation levels of 150 ppm or less can be fed without increasing lipid oxidation, pigment oxidation, or both.
Neither cooking loss percentage nor Warner-Bratzler shear force was affected (P 0.80) by dietary treatment (Table 5
) or 7-d aging period (results not shown). Field et al. (1985) reported that shear force values were not affected by drenching sheep with FeO, and, although Gariépy et al. (1998) noted no effect of dietary Fe level on cooking loss percentage, veal chops from calves fed a grain-based diet with high levels of Fe (77 to 217 ppm) were tougher than chops from calves fed a low-Fe (4 to 45 ppm) milk diet.
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IMPLICATIONS
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Results of this study suggest that minor improvements in pork color during retail display can be achieved by feeding an additional 100 ppm Fe. However, supplementing swine diets with Fe had no beneficial effects on performance or carcass composition of growing-finishing pigs. Thus, these results indicate that current dietary Fe recommendations are sufficient for optimal live pig performance, pork carcass composition, and pork quality.
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Footnotes
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1 We thank Zinpro Corp. for financial support of this experiment, as well as K. Richardson and the employees at Bryan Foods Inc. (West Point, MS) for their hospitality and assistance with pig slaughter, carcass fabrication, and pork loin procurement. Additionally, we gratefully acknowledge the assistance of A. Hays for animal care and performance data collection and J. Stephenson for assistance with loin fabrication. 
3 Current address: Swift & Co., Greeley, CO.
4 Current address: Department of Animal Sciences and Industry, Kansas State University, Manhattan.
2 Corresponding author: japple{at}uark.edu
Received for publication April 10, 2006.
Accepted for publication October 25, 2006.
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Abstract
INTRODUCTION
