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Effect of supplemental manganese on performance and carcass characteristics of growing-finishing swine¹

J. K. Apple^*,2, W. J. Roberts^*,3, C. V. Maxwell^*, C. B. Boger^*, T. M. Fakler, K. G. Friesen^* and Z. B. Johnson^*

^* Department of Animal Sciences, University of Arkansas, Fayetteville 72701; and and Zinpro Corporation, Eden Prairie, MN 55344

	Abstract

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Three hundred sixteen crossbred pigs were used in two experiments to determine the effect of supplemental manganese source and dietary inclusion level during the growing-finishing period on performance and pork carcass characteristics. All pigs were blocked by weight, and treatments were assigned randomly to pens within blocks. In Exp. 1, a total of 20 pens (five pigs/pen) was randomly assigned to one of five dietary treatments consisting of control grower and finisher diets, or control diets supplemented with either 350 or 700 ppm (as-fed basis) Mn either from MnSO₄ or a Mn AA complex (MnAA). In Exp. 2, a total of 36 pens (six pigs per pen) was assigned randomly to one of six dietary treatments formulated with 0, 20, 40, 80, 160, or 320 ppm (as-fed basis) Mn from MnAA. Pigs were slaughtered when the lightest block averaged 120.0 kg (Exp. 1) or at a mean BW of 106.8 kg (Exp. 2). Neither ADG nor ADFI was affected (P > 0.21) by Mn source or high inclusion level (Exp. 1); however, across the entire feeding trial, pigs consuming 320 ppm Mn from MnAA were more (P < 0.04) efficient than pigs fed diets formulated with 20 to 160 ppm Mn from MnAA (Exp. 2). Color scores did not differ (P > 0.79) at the low inclusion (20 to 320 ppm Mn) levels used in Exp. 2; however, in Exp. 1, the LM from pigs fed Mn tended to receive higher (P = 0.10) American color scores than that of pigs fed the control diet, and Japanese color scores were higher for the LM from pigs fed diets containing 350 ppm Mn from MnAA than 350 Mn from ppm MnSO₄ or 700 ppm Mn from MnAA (source x inclusion level; P = 0.04; Exp. 2). Chops of pigs fed 350 ppm Mn from MnAA were darker than the LM of pigs fed 350 ppm Mn from MnSO₄, and 700 ppm Mn from MnAA diets (source x inclusion level; P = 0.03; Exp. 1), but L* values were not (P = 0.76) affected by lower MnAA inclusion levels (Exp. 2). Even though the LM tended to became redder as dietary MnAA inclusion level increased from 20 to 320 ppm Mn (linear effect; P < 0.10), a* values were not (P = 0.71) altered by including 350 or 700 ppm Mn (Exp. 1). Chops of pigs fed MnAA had lower cooking losses (P = 0.01) and shear force values (P = 0.07) after 2 d of aging than did chops from pigs fed diets formulated with MnSO₄. Results from these experiments indicate that feeding 320 to 350 ppm Mn from MnAA during the growing-finishing period may enhance pork quality without adversely affecting pig performance or carcass composition.

Key Words: Carcass Composition • Growth • Manganese • Meat Quality • Pork • Swine

	Introduction

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Dietary requirements for Mn in swine diets are quite low and not well established, and are largely based on research conducted some 30 yr ago with inorganic sources of Mn. Grummer et al. (1950) observed improvements in growth rate and feed efficiency in pigs fed supplemental Mn. Conversely, neither Plumlee et al. (1956) nor Leibholz et al. (1962) reported differences in ADG and efficiency between pigs fed diets supplemented with or without Mn. Although not statistically significant, Svajgr et al. (1969) noted that feed efficiency was improved by inclusion of 100 ppm Mn in swine finishing diets. None of the aforementioned studies measured the effect of supplemental Mn on pork carcass composition or quality.

Manganese and magnesium are both divalent, transition metal cations that may be interchangeable in several functions within the body (Chiesi and Inesi, 1981; Campos and Beauge, 1988; Gaillard et al., 1996). It was hypothesized, therefore, that including Mn in swine growing-finishing diets might cause beneficial effects similar to supplementing swine diets with Mg on pork color (D’Souza et al., 1998; Apple et al., 2000a; Hamilton et al., 2002) and water-holding capacity (D’Souza et al., 2000; Hamilton et al., 2002). Thus, the objectives of this research were to assess the effects of Mn source (Exp. 1) and dietary inclusion level (Exp. 1 and 2) on live performance, carcass composition, and pork quality of growing-finishing swine.

	Materials and Methods

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Animals and Diets
In Exp. 1, 100 barrows and gilts (offspring of Yorkshire x Landrace dams mated to Duroc x Hampshire sires) with an initial BW of 26.2 ± 1.7 kg were blocked into four weight blocks (25 pigs per block) and allotted at random into five pens (five pigs per pen) within blocks, with stratification across pens based on sex and litter origin. Within blocks, pens were randomly assigned to one of five dietary treatments (as-fed basis): 1) control corn-soybean meal grower and finisher diets; 2) control diets supplemented with 350 ppm Mn from MnSO₄; 3) control diets supplemented with 700 ppm Mn from MnSO₄; 4) control diets supplemented with 350 ppm Mn from Availa-Mn, a Mn AA complex (MnAA; Zinpro Corp., Eden Prairie, MN); or 5) control diets supplemented with 700 ppm Mn from MnAA.

In Exp. 2, 216 crossbred barrows and gilts (EB x line-348; DeKalb Choice Genetics, St. Louis, MO) with an initial BW of 23.8 ± 3.4 kg were sorted into six weight blocks of 36 pigs per block. Pigs within each block were allotted randomly to pens (six pigs per pen) and stratified across pens according to gender and litter origin. Then, pens within each block were assigned randomly to one of six dietary treatments consisting of control corn-wheat middlings-soybean meal grower and finisher diets with no supplemental Mn, and the diets supplemented with either 20, 40, 80, 160, or 320 ppm Mn from MnAA.

Pigs in both experiments were fed a four-phase dietary program with the transition from Grower-I to Grower-II, Grower-II to Finisher-I, and Finisher-I to Finisher-II phases occurring when average block weight reached 36.4, 68.2, and 90.9 kg, respectively. Additionally, diets in both experiments (Table 1) were formulated to be isolysinic (lysine content of Grower-I, Grower-II, Finisher-I, and Finisher-II diets was 1.16, 0.95, 0.72, and 0.57%, respectively, as-fed basis) and isocaloric (ME content of Grower-I, Grower-II, Finisher-I, and Finisher-II diets was 3.41, 3.32, 3.31, and 3.30 Mcal/kg, respectively, as-fed basis). Although the mineral premix incorporated in all diets was devoid of Mn, feedstuffs supplied from 44 to 50 ppm Mn, and within the manganese-treated diets, MnSO₄ (Exp. 1) and Availa-Mn (Exp. 1 and 2) were added at the expense of cornstarch (Table 1). All diets were formulated to meet or exceed NRC (1998) AA, energy, and other nutrient requirements for growing-finishing swine.

Carcass Data Collection
In Exp. 1, when the lightest block of pigs averaged 120 kg, all pigs were transported approximately 515 km and slaughtered at a small, commercial pork-packing plant (Fineberg Packing Co., Memphis, TN) after a 12-h rest period. Pigs were slaughtered according to industry-accepted procedures, and carcasses were conventionally air-chilled at 2°C for 24 h. University of Arkansas personnel were unable to collect individual hot carcass weights because plant policy required weighing several carcasses at a time; however, after the chilling period, midline backfat depths opposite the first rib, last rib, and last lumbar vertebra were measured to calculate average backfat thickness, and loins were marked between the 10th and 11th ribs in order to measure LM area upon arrival at the University of Arkansas. Bone-in pork loins from left sides were captured during fabrication, wrapped in parchment paper, boxed, and transported to the University of Arkansas Red Meat Abattoir under refrigeration.

When the mean weight of pigs in Exp. 2 was 106.8 kg, all pigs were transported approximately 760 km to a commercial pork packing plant (Bryan Foods, Inc., West Point, MS). Pigs were slaughtered after a 12-h rest period at the plant, and 10th-rib fat and LM depths were measured online with a Fat-O-Meater 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 hot carcass weight was recorded. Carcasses were subsequently subjected to a conventional spray-chilling system for 24 h. Before carcass fabrication, midline backfat depths were recorded to calculate average backfat depth. During carcass fabrication, boneless pork loins 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, pork loins were cut between the 10th and 11th ribs, and, in Exp. 1, the area of the LM was traced onto acetate paper, and subsequently measured using a compensating planimeter. In Exp. 1, two 2.5-cm-thick and two 3.8-cm-thick LM chops were sliced posterior of the 11th rib, whereas in Exp. 2, only two 2.5-cm-thick LM chops were removed from the posterior portion of the loin.

After a 45-min bloom period at 4°C, two 2.5-cm-thick LM chops were visually evaluated for marbling (1 = devoid [1% i.m. fat] to 10 = abundant [10% i.m. fat]; 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 Exp. 1, LM chops were also subjectively evaluated for firmness/wetness (1 = very soft/watery to 5 = very firm/dry; NPPC, 1991). Also, L*, a*, and b* values (CIE, 1976) were determined from a mean of four random readings (two readings for each chop) made with a Hunter MiniScan XE (model 45/0-L; Hunter Associates Laboratory, Reston, VA) using illuminate C and a 10° standard observer. The saturation index, or chroma (C*), was also calculated as C* = (a*² + b*²). It is a measure of the total color, or vividness of the color, of the LM. After quality data collection in Exp. 1, both 2.5-cm-thick chops were wrapped in freezer paper; one chop was immediately frozen at –20°C (2-d aged chops), whereas the second chop was aged for an additional 7 d at 4°C (9-d aged chops), and then frozen at –20°C before cooking and Warner-Bratzler shear force (WBSF) determinations.

The two 3.8-cm-thick LM chops in Exp. 1 were used to measure drip loss according to the suspension procedure of Honikel et al. (1986), as described in detail by Apple et al. (2000a). As for the LM chops in Exp. 2, each boneless chop was weighed, placed onto Styrofoam trays with an absorbent pad, overwrapped with an oxygen-permeable, polyvinyl chloride film, and stored at 4°C for 48 h. Then, chops were removed, blotted with paper towels, and reweighed. The difference between weights was divided by the initial chop weight to calculate the percentage of moisture loss. Additionally, in both experiments, a 2-g sample 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 (model 300731.1; Denver Instrument Co., Arvada, CO) attached to a pH/ion/FET-meter (model AP25; Denver Instrument Co.).

Warner-Bratzler Shear Force Determinations (Exp. 1)
Longissimus muscle chops were thawed for 16 h at 2°C, deboned, weighed, and then cooked to an internal temperature of 71°C in a commercial convection oven (Zephaire E; 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 in the geometric center of each chop and attached to a multichannel data logger (model 245A; VAS Engineering, Inc., San Diego, CA). Chops were turned once during cooking when the internal temperature reached 35°C. Immediately after removal from the oven, chops were blotted dry on paper towels, weighed, and the difference between pre and postcooked weights was used to calculate cooking loss percent. Chops were chilled at 4°C for 24 h, and at least five good 1.3-cm-diameter cores were removed parallel to the muscle fiber orientation, and each core was sheared once through the center with a Warner-Bratzler shear force device attached to an Instron Universal Testing Machine (model 4466; In-stron Corp., Canton, MA). The Instron was equipped with a 55-kg tension/compression load cell, and the crosshead speed was set at 250 mm/min. Shear force values of the five cores from each chop were averaged for statistical analyses.

Data Analyses
Data from Exp. 1 were analyzed as a randomized complete block design with treatments arranged in a 2 x 2 factorial (with control) design, whereas data from Exp. 2 were analyzed as a randomized complete block design, with blocks based on initial BW. Analysis of variance was generated using the mixed-model procedure (PROC MIXED) of SAS (SAS Inst., Inc., Cary, NC). The experimental unit for all performance data was pen; however, because at least one pen in each experiment was not represented by more than one observation, carcass was considered as the experimental unit in the analysis of pork carcass composition and pork quality data. Dietary treatment was included in the model as a fixed effect, and block and the block x pen x treatment (performance data), or block x pen x carcass x treatment (carcass data) were included in the models as random effects. Least squares means were computed for the dietary treatments, and preplanned orthogonal contrasts were used to accurately compare untreated controls to Mn-fed pigs, Mn sources (manganese sulfate vs. Availa-Mn), dietary inclusion level (350 vs. 700 ppm Mn), and the source x inclusion level interaction (Exp. 1). Furthermore, in Exp. 2, linear, quadratic, and cubic polynomials were used to detect the response to dietary inclusion level (20, 40, 80, 160, and 320 ppm) of Mn from Availa-Mn, and preplanned, orthogonal comparisons of pigs fed the control vs. all Mn diets, as well as the highest inclusion level (320 ppm Mn) vs. all other inclusion levels (20, 40, 80, and 160 ppm Mn), were included in the statistical model.

	Results

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Experiment 1
Neither ADG nor ADFI was affected (P > 0.21) during any feeding phase or across the entire feeding trial by dietary Mn source or inclusion level (Table 2). However, during the Grower-I phase, pigs fed the control diet tended to have higher (control vs. all Mn diets; P = 0.08) G:F than pigs fed diets supplemented with Mn. Additionally, pigs fed 350 ppm Mn from MnSO₄ or 700 ppm Mn from MnAA had greater G:F than pigs fed 700 ppm Mn from MnSO₄ or 350 ppm Mn from MnAA during the Grower-II phase (source x inclusion level; P = 0.06). Although G:F was not affected by Mn source (P = 0.97) or inclusion level (P = 0.28) during the early-finisher phase, pigs fed MnSO₄ tended to be more efficient during the late-finisher phase than those fed MnAA (source; P = 0.06). Over the entire feeding period, pigs consuming diets with 350 ppm Mn from MnSO₄ or 700 ppm Mn from MnAA tended to have higher G:F than those fed diets with 350 ppm Mn from MnAA (source x inclusion level; P = 0.09). Live weights of pigs at the conclusion of each feeding phase were not affected by Mn source (P > 0.62) or dietary inclusion level (P > 0.11).

Experiment 2
During the Grower-I phase, neither ADG nor G:F was affected by dietary Mn (P > 0.15); however, pigs fed MnAA consumed less feed than pigs fed the control diets (control vs. all Mn diets; P < 0.01) during the Grower-I phase (Table 5). Additionally, during the early growing phase, pigs fed 40 to 320 ppm Mn tended to have lower ADFI than pigs fed 20 ppm (cubic effect; P = 0.10). Even though dietary Mn did not (P > 0.31) affect performance during the Grower-II phase, pigs fed 40 and 320 ppm Mn had higher ADG than pigs fed 160 ppm MnAA (cubic effect; P = 0.02) during the early-finisher phase. Furthermore, there was a tendency during the Finisher-I phase, for pigs fed the control diet to be less efficient (lower G:F) than pigs consuming the Mn diets (control vs. all Mn diets; P = 0.06), and, within the MnAA-diets, pigs fed 40 and 320 ppm Mn tended to more efficient than pigs fed diets containing 20 and 160 ppm Mn from MnAA (cubic effect; P = 0.06). Dietary Mn inclusion level failed (P > 0.13) to alter pig performance during the late-finishing phase; however, across the entire trial, feed efficiency (G:F) was greater (P = 0.04) in pigs fed diets containing 320 ppm Mn than those fed the control diets or diets with 20, 80, or 160 ppm Mn. Live weights, recorded at the conclusion of each feeding phase, were not different (P > 0.10) among the dietary treatments.

	Discussion

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Carcass Composition
There is limited information available concerning the effects of dietary Mn on pork carcass composition. Grummer et al. (1950) reported that carcass weights and dressing percents were highest in pigs fed diets supplemented with 160 ppm Mn compared with pigs fed diets with no supplemental Mn, and Plumlee et al. (1956) observed that gilts fed Mn-deficient (0.5 ppm Mn) diets were visually fatter than pigs fed diets with 40 ppm Mn. Additionally, Christianson et al. (1989) reported that backfat of gestating and lactating sows increased as the dietary Mn level increased from 5 to 20 ppm. In Exp. 1, there was a tendency for decreasing backfat by feeding Mn at very high levels (700 ppm); however, feeding growing-finishing diets with lower levels of Mn (350 or less) failed to beneficially alter carcass fatness, and dietary Mn had no beneficial effects on muscling measures.

Pork Quality
Manganese and Mg are both divalent, transition metal cations that may be interchangeable in several functions within the body. For example, the body can replace Mn with Mg with similar efficiency in Mn-activated enzymes (Wapnir, 1990), whereas Mn can replace Mg in Mg-activated enzymes, such as calcium ATPase (Chiesi and Inesi, 1981) and sodium-potassium ATPase (Campos and Beauge, 1988). Gaillard et al. (1996) reported that supplementing rat diets with Mn increased urinary Mg levels; however, Sanchez-Morito et al. (1999) observed that Mn excretion was decreased, and Mn absorption and retention in skeletal muscle, heart, and kidney was increased, when rats were fed a Mg-deficient diet. Therefore, it is plausible that the beneficial effects of supplementing swine diets with Mn on pork quality are comparable to those noted when supplementing swine diets with Mg.

The improvements in pork color from pigs fed diets containing Mn (present study) are quite similar to the results reported for pigs fed increased levels of Mg. In the first of two experiments, Apple et al. (2000a) reported that formulating the growing-finishing diets of pigs with magnesium mica resulted in improvements in visual color scores, as well as a* and chroma values. Additionally, several studies have demonstrated that short-term (less than 5 d) supplementation of Mg improved pork color, especially L* values (D’Souza et al., 1998, 1999; Hamilton et al., 2002).

The effects of feeding Mg-supplemented diets to finishing pigs on water-holding capacity are somewhat conflicting. D’Souza et al. (2000) and Hamilton et al. (2002) reported that supplementing Mg to swine finishing diets 2 to 5 d before slaughter reduced the percentage of drip loss from the LM. On the other hand, neither long-term (Apple et al., 2000a, 2002) nor short-term (van Laack, 2000; Hamilton et al., 2003) Mg supplementation affected the water-holding capacity of fresh pork, which is consistent with the observation that dietary Mn, regardless of source or inclusion level, failed to altered drip/moisture losses in the LM.

Loin chops from pigs fed Mn-fortified diets received similar marbling scores to chops from pigs fed the un-supplemented, control diets. This finding is consistent with those of Apple et al. (2000a, 2002) and Hamilton et al. (2002, 2003), who reported that supplementing swine diets with Mg had no effect of marbling score.

Interestingly, chops from pigs fed MnAA had lower cooking losses and WBSF values than chops from pigs fed MnSO₄ diets at 48 h postmortem; however, after the 9-d aging period, no differences were detected in percent cooking loss or shear force values. Even though most of the Mg-supplementation studies did not measure cooking losses or shear force values, Apple et al. (2001) reported that dietary Mg, regardless of supplementation level, had no effect on cooking losses or shear force values of pork LM chops. However, LM chops from sheep fed one source of Mg (unweathered magnesium mica) were actually tougher than chops from sheep fed an unsupplemented finishing diet or diets containing magnesium oxide or weathered magnesium mica (Apple et al., 2000b). There is no evidence to suggest that either Mn or Mg alter postmortem proteolysis; therefore, additional research is required to discern how dietary Mn may affect postmortem tenderization.

	Implications

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Results of the current study indicate that including Availa-Mn (a manganese amino acid complex) in the diets of growing-finishing pigs at a rate of 320 to 350 ppm Mn may enhance pork quality, especially fresh pork color and cooked pork tenderness, without detrimental effects on performance or carcass composition. Moreover, including 320 ppm Mn from Availa-Mn may improve efficiency during the growing-finishing phase. However, dietary inclusion of 700 ppm Mn, regardless of source, did not produce any beneficial effects on live pig performance or pork quality.

	Footnotes

 
¹ The authors express their appreciation to Zinpro Corp. for financial support of these experiments. Additionally, the authors gratefully acknowledge the assistance of A. Hays and R. Hinson for animal care and performance data collection, and L. Rakes, J. Stephenson, J. Leach, J. Jimenez, and R. Miller for assistance in loin fabrication and data collection.

³ Current address: Eastern Oklahoma State College, Wilburton 74578.

² Correspondence: B-103C AFLS Bldg. (phone: 479-575-4840; fax: 479-575-7294; e-mail: japple{at}uark.edu).

Received for publication February 23, 2004. Accepted for publication July 14, 2004.

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