Effect of magnesium mica on performance and carcass quality of growing-finishing swine J. K. Apple, C. V. Maxwell, B. deRodas, H. B. Watson and Z. B. Johnson J ANIM SCI 2000, 78:2135-2143.
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Effect of magnesium mica on performance and carcass quality of growing-finishing swine1 J. K. Apple2, C. V. Maxwell, B. deRodas3, H. B. Watson4, and Z. B. Johnson Department of Animal Science, University of Arkansas, Fayetteville 72701
ABSTRACT: A total of 240 crossbred pigs were used in two experiments to determine the effect of feeding magnesium mica (MM) during the growing-finishing period on animal performance and pork carcass characteristics. All pigs were blocked by weight, and treatments were assigned randomly to pens (five pigs/pen) within blocks. In each experiment, eight pens were allotted randomly to one of three treatments: 1) a negative control corn-soybean meal starter, grower, and finisher diet devoid of supplemental magnesium; 2) the control diets supplemented with 1.25% MM; and 3) the control diets supplemented with 2.50% MM. In Exp. 1, pigs were slaughtered at the University of Arkansas Red Meat Abattoir, whereas pigs in Exp. 2 were transported to a commercial pork packing plant and slaughtered according to industry-accepted procedures. In both experiments, dietary supplementation of MM had no (P > .10) effect on ADG, ADFI, or gain:feed ratio at any phase during the growing-finishing period. In Exp. 1, MM supplementation had no (P > .10) effect on carcass fatness or muscling. More-
over, Japanese color scores were not (P > .10) affected by feeding pigs MM; however, American color scores increased linearly (P < .01) with increasing levels of MM in the diet. Although MM supplementation did not (P > .10) affect L* and b* values for the longissimus muscle (LM), there was a linear increase (P < .05) in LM a* and chroma values associated with increased MM levels in swine diets. In Exp. 2, carcasses from pigs fed 1.25% MM had less (P < .05) fat opposite the LM at the 10th rib than untreated controls and pigs fed 2.50% MM and higher (P < .10) percentages of muscle than carcasses of untreated controls. Moreover, the LM from pigs fed 1.25% MM was less (P < .05) red and less (P < .05) yellow than the LM from pigs fed the control or 2.50% MM-supplemented diets. Drip loss from the LM was unaffected (P > .10) by inclusion of MM in the diet. Results from this study confirm that inclusion of MM, an inexpensive, inorganic magnesium source, in diets of growing-finishing swine has beneficial effects on pork carcass cutability and quality with no deleterious effects on live animal performance.
Key Words: Carcass Composition, Diet, Magnesium, Meat Quality, Pigs 2000 American Society of Animal Science. All rights reserved.
Introduction Magnesium (Mg) is the second most abundant intracellular metal ion in cells, and it activates numerous 1
Technical article no. 99108 from the Arkansas Agric. Exp. Sta. The authors wish to express their appreciation to Micro-Lite, Inc., Chanute, KS for donation of magnesium mica and financial support of this project. Additionally, the authors gratefully acknowledge the assistance of Ben Wheeler (Seaboard Farms, Inc.) and Brent Green (PIC, USA), as well as Fred Pohlman, Lillie Rakes, Jesse Davis, Jerry Stephenson, John Hankins, Levi McBeth, and Matt Stivarius in animal slaughter, carcass fabrication, and data collection; and Joe Leibrandt, Ashley Hays, Ellen Davis, and Lance Kirkpatrick for animal care and performance data collection. 2 Correspondence: phone: (501) 575-4840; fax: (501) 575-7294; Email:
[email protected]. 3 Current address: Cenex/Land O’Lakes, Ft. Dodge, IA 50501. 4 Current address: Cargill, Inc., Springdale, AR 72764. Received October 18, 1999. Accepted March 3, 2000.
J. Anim. Sci. 2000. 78:2135–2143
enzymes in the central pathways of intermediary cellular metabolism (Heaton, 1973). In meat animals, Mg supplementation has traditionally been used as a precautionary treatment to prevent metabolic disorders associated with a Mg deficiency (Littledike et al., 1983). However, recent information has shown that Mg supplementation may reduce stress responses in animals (Kietzmann and Jablonski, 1985; D’Souza et al., 1998) and have beneficial effects on meat quality (Schaefer et al., 1993; D’Souza et al., 1998). The inclusion of Mg in swine finishing diets has been shown to reduce plasma cortisol and catecholamine concentrations during transportation stress (Niemack et al., 1979; Kietzmann and Jablonski, 1985). Kuhn et al. (1981) showed that Mg-supplemented pigs were visually calmer upon delivery at the packing plant, and pork quality was also improved by Mg supplementation. Feeding finishing swine a diet including Mg fumarate resulted in higher initial muscle pH values
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and less pale, more desirably colored pork (Otten et al., 1992). Furthermore, dietary inclusion of Mg aspartate reduced drip loss, improved pork color, and reduced the incidence of pale, soft, and exudative (PSE) pork (Schaefer et al., 1993; D’Souza et al., 1998). Magnesium mica (MM), an inorganic, layered silicate product containing 8% Mg, has been used primarily in the feed industry as a pellet binder. Inclusion of MM in feedlot diets of cattle was found to increase mean marbling scores and percentage of carcasses grading USDA Choice or higher (Coffey and Brazle, 1995); however, no studies have been reported on supplementing swine diets with MM. Therefore, the objective of this study was to determine the effect of feeding MM during the growing-finishing period on live animal performance and pork carcass quality.
Materials and Methods Animals and Diets. Crossbred gilts and barrows (n = 120) from Yorkshire and Yorkshire-cross composite females (Lean Value Sires, New Carlisle, OH) mated to Duroc × Hampshire boars, with an average initial BW of 24.2 ± 3.2 kg, were used in Exp. 1 (begun on September 22, 1997, and completed on December 15, 1997). An additional 120 crossbred gilts and barrows, from Yorkshire-cross females mated to Duroc × Hampshire sires (The Pork Group, Tyson Foods, Rogers, AR), with a mean initial weight of 27.2 ± 2.7 kg were used in Exp. 2 (begun on September 7, 1998, and completed on December 9, 1998). In both experiments, pigs were moved from the University of Arkansas Nursery to the University of Arkansas Swine Growing-Finishing Facility and blocked by BW into eight blocks. Pigs were then allotted to pens (three pens/block) based on sex and litter origin, and one of three treatments was assigned randomly to pens (five pigs/pen) within blocks. Pigs were fed a three-phase diet with transition from starter to grower when the average block BW was 34.5 and 38.1 kg for Exp. 1 and Exp. 2, respectively, and from grower to finisher when the mean weight of each block reached 66.0 and 68.4 kg for Exp. 1 and 2, respectively. In each experiment, eight pens were allotted randomly to one of three treatments: 1) a negative control corn-soybean meal starter, grower, and finisher diet devoid of supplemental magnesium; 2) the control starter, grower, and finisher diets supplemented with 1.25% MM (Micro-Lite, Chanute, KS); and 3) the control starter, grower, and finisher diets supplemented with 2.50% MM (Table 1). Within the MM-treated diets, MM was added at the expense of corn. All diets were formulated to meet or exceed NRC (1988) requirements for growing-finishing swine, and starter, grower, and finisher diets contained 1.10, .95, and .85% lysine, respectively (Table 1). Calcium and phosphorus levels were maintained at .8 and .65%, respectively, during the starter and grower phases, then reduced to .7 and .6%, respectively, during the
finishing phase. Individual pig weights were measured weekly, and feed disappearance was recorded at 7-d intervals during each phase to calculate ADG, ADFI, and gain:feed ratio (G:F). Carcass Data Collection. In Exp. 1, pigs were removed from the experiment and slaughtered at the University of Arkansas Red Meat Abattoir weekly as blocks reached an average minimum BW of 102.3 kg. Pigs were slaughtered according to industry-accepted procedures, and carcasses were conventionally chilled at 2°C for 24 h. Fat depth opposite the first rib, last rib, and last lumbar vertebra was measured to calculate average backfat thickness. Then, the right side of each carcass was ribbed between the 10th and 11th thoracic vertebrae. Fat depth over the longissimus muscle (LM) was recorded, and the cross-section of the LM was traced onto acetate paper and LM area was measured using a compensating planimeter. The NPPC (1991) equation for lean pork containing 5% fat was used to calculate the percentage muscle for each carcass. The LM from each carcass was subjectively evaluated for marbling (1 = devoid to practically devoid; 2 = traces to slight; 3 = small to modest; 4 = moderate to slightly abundant; and 5 = moderately abundant or greater), American color (1 = pale pinkish gray; 2 = grayish pink; 3 = reddish pink; 4 = purplish red; and 5 = dark purplish red; NPPC, 1991), and Japanese color (1 = pale gray to 6 = dark purple) by an experienced university faculty member after a 30-min “bloom” period. The Japanese color standards consist of six plastic disks with a meat-like appearance developed from objective colorimetric measures (Nakai et al., 1975). Subsequent objective color of the LM was measured with a Hunter MiniScan XE (Model 45/0-L, Hunter Associates Laboratory, Reston, VA). Commission Internationale de l’Eclairage L*, a*, and b* values (CIE, 1976) were determined from the mean of three random readings on the LM using illuminant C and a 10° standard observer. The spectrophotometer had a 22-mm aperture and was calibrated against a standard white tile (No. M04207 with X = 81.1, Y = 85.9, and Z = 91.6; Hunter Associates Laboratory). The hue angle represents a change from red color and was calculated as: tan−1(b*/a*). The saturation index, or chroma, represents the color intensity of the LM and was calculated as:√a*2 + b*2 (Minolta, 1993). In Exp. 2, when the lightest block of pigs averaged 106.8 kg, all pigs were transported approximately 724 km to a commercial pork slaughter/fabrication plant (Seaboard Farms, Guymon, OK). Pigs were slaughtered after a 12-h rest period, and carcasses were chilled rapidly for 6 h at −26°C, followed by an 18-h “tempering” period at 2°C. Twenty-four hours after slaughter, 10th-rib fat and LM depth were measured on-line with a Fat-O-Meater automated probe (model no. S71; SFK Technology A/S, Cedar Rapids, IA) inserted between the 10th and 11th ribs at a distance
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Table 1. Composition and costs of experimental diets Starter diets Ingredient, % Corn Soybean meal (48% CP) Animal and vegetable fat Dicalcium phosphate Magnesium mica Calcium carbonate Salt Mineral premixa Vitamin/trace mineral premixb Tylosin-40 Copper sulfate Ethoxyquin Calculated total composition, % Crude protein Lysine Methionine Methionine and cysteine Threonine Tryptophan Magnesium Calcium Phosphorus Metabolizable energy, kcal/kg Diet ingredient costs, U.S.$/45.45 kg Experiment 1 Experiment 2
Grower diets
Finisher diets
0
1.25
2.50
0
1.25
2.50
0
1.25
2.50
61.775 30.75 4.0 1.55 .0 .82 .5 .15 .25 .125 .05 .03
60.275 31.00 4.0 1.55 1.25 .82 .5 .15 .25 .125 .05 .03
59.095 30.90 4.0 1.60 2.50 .80 .5 .15 .25 .125 .05 .03
66.975 25.60 4.0 1.65 .0 .77 .5 .15 .15 .125 .05 .03
65.725 25.60 4.0 1.65 1.25 .77 .5 .15 .15 .125 .05 .03
64.295 25.75 4.0 1.70 2.50 .75 .5 .15 .15 .125 .05 .03
71.115 21.90 4.0 1.45 .0 .68 .5 .10 .125 .05 .05 .03
69.865 21.90 4.0 1.45 1.25 .68 .5 .10 .125 .05 .05 .03
68.615 21.90 4.0 1.50 2.50 .63 .5 .10 .125 .05 .05 .03
20.17 1.10 .32 .67 .78 .24 .18 .8 .65 712.19
20.16 1.10 .32 .67 .78 .24 .28 .8 .65 703.34
20.01 1.10 .32 .67 .78 .24 .38 .8 .65 694.30
18.11 .95 .29 .61 .70 .21 .18 .8 .65 712.94
18.00 .95 .29 .61 .70 .21 .28 .8 .65 704.10
17.95 .95 .29 .61 .70 .21 .38 .8 .65 695.05
16.67 .85 .27 .57 .64 .19 .18 .6 .60 716.34
16.56 .85 .27 .57 .64 .19 .27 .6 .60 707.50
16.45 .85 .27 .57 .64 .19 .37 .6 .60 698.67
9.20 6.87
9.18 6.85
9.12 6.83
8.81 6.64
8.77 6.61
8.72 6.60
8.07 6.09
8.04 6.06
7.94 6.03
a
Premix consisted of 11.0% Fe, 11.0% Zn, 2.6% Mn, 1.1% Cu, .02% I, and .02% Se (Nutra Blend Corp., Neosho, MO). Premix consisted of 909,090.9 IU vitamin A, 136,363.6 IU vitamin D3, 3,636.4 IU vitamin E, 3.6 mg vitamin B12, 363.6 mg vitamin K, 818.2 mg riboflavin, 2,727.3 mg d-pantothenic acid, and 4,545.5 mg niacin per kg (Nutra Blend Corp., Neosho, MO). b
of approximately 7 cm from the midline. Carcasses were then fabricated into subprimal cuts according to Institutional Meat Purchase Specifications (IMPS) for Fresh Pork Products (USDA, 1995), and LM pH was measured with an automated pH probe (pH-Star, SFK Technology A/S). Subjective scores for muscle firmness (1 = very soft; 2 = soft; 3 = slightly firm; 4 = firm; and 5 = very firm), marbling (NPPC, 1991), and color (American and Japanese color standards) were assigned by a trained, experienced plant employee on the LM, at the posterior end of boneless pork loins (IMPS #412E), after a 30-min “bloom” period. Pork loins were subsequently vacuum-packaged in oxygenimpermeable bags (sales type B650, 20.1 cm × 78.7 cm; Cryovac North America, Duncan, SC), packed in Styrofoam containers, and shipped to the University of Arkansas Red Meat Abattoir for further quality measurements. At approximately 48 h after slaughter, pork loins were removed from packaging material and blotted dry with paper towels, and a 5-cm portion of the cranial end of the loin was removed perpendicular to the length of the loin. A 2.54-cm-thick LM chop was removed for color evaluations and two 3-cm-thick LM chops were removed for drip loss determinations. After a 45-min “bloom” period, L*, a*, and b* values (CIE, 1976) were determined from the mean of three random
readings made with the Hunter MiniScan XE. Hue angle and saturation index for each LM chop were calculated from CIE a* and b* values (Minolta, 1993). Drip loss was determined following the suspension procedure of Honikel et al. (1986). Briefly, a 3-cmdiameter core was manually removed from each 3-cmthick LM chop, weighed, and suspended on a fishhook (barb removed) mounted to the lid of a plastic container (46 × 66 × 38 cm deep Dur-X Food Box, Rubbermaid Commercial Products LLC, Winchester, VA), and stored for 48 h at 4°C. After storage, each core was removed from its hook, blotted dry with a paper towel, and reweighed. The loss in weight was divided by the original core weight and multiplied by 100 to calculate drip loss percentage. Data Analyses. Performance and carcass data were analyzed as a randomized complete block design with pen as the experimental unit and blocks based on initial BW. Analysis of variance was generated using the GLM procedure of SAS (1990), with dietary treatment as the main effect in the model. Least squares means were computed for the main effect and were separated statistically using the probability of difference (PDIFF) option (SAS, 1990). Linear and quadratic polynomials were used to detect the response to inclusion level of MM in the diet (0, 1.25, and 2.50%). Frequencies of American and Japanese color scores were
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analyzed by chi-square analysis (Ott, 1988), using the frequency procedure of SAS (1990).
Results Experiment 1. Inclusion of MM in growing-finishing diets at either 1.25 or 2.50% had no (P > .10) effect on ADG, ADFI, or G:F during the starter, grower, or finisher phases, or during the entire trial (Table 2). In accordance with the performance data, live weights did not differ (P > .10) among MM-treated and control pigs at any phase of the growing-finishing period. The effects of MM on carcass characteristics are presented in Table 3. Hot carcass weight, dressing percentage, average backfat thickness, 10th-rib fat depth, LM area, and percentage muscle were not (P > .10) affected by inclusion of MM in the diet. Mean American color scores increased linearly (P < .01) with increasing levels of MM in the diet. Observed improvements in American color scores were due to a substantial decrease in carcasses with an American color score of 1 (indicative of PSE pork) from 15.4% in pigs fed the control diet to only 2.5% of the carcasses from pigs fed diets containing 2.50% MM (Table 4). Moreover, the percentage of carcasses receiving color scores of 3 increased from 10.26% in pigs fed the control diet to 25.0% in pigs fed diets containing 2.50% MM; the percentage of carcasses receiving a color score of 2 was similar across dietary treatments. Mean Japanese color scores were not (P > .10) affected by inclusion of supplemental MM (Table 3);
however, the percentage of carcasses receiving an undesirable score of 1 decreased and the percentage of carcasses receiving a desirable score of 4 increased in pigs fed diets containing MM (Table 4). The magnitude of response was similar to that observed with American color scores, with a decrease in carcasses with a color score of 1 from 12.82% in pigs fed the control diets to 0% of the carcasses from pigs fed diets 1.25 or 2.50% MM. Additionally, the percentage of carcasses with a desirable color score of 4 increased from 12.82% in pigs fed the control diet to 22.22 and 22.50% in pigs fed diets containing 1.25 and 2.50% MM, respectively. Feeding diets containing either 1.25 or 2.5% MM had no (P > .10) appreciable effects on CIE L* or b* values for the LM (Table 3). However, the LM from MM-supplemented pigs had higher (P < .05) CIE a* values, indicating a redder colored LM, than the LM from pigs fed the control diets. Hue angle decreased linearly (P < .05) and saturation index (chroma) increased linearly (P < .05) with increasing levels of MM included in the diet. The LM from pigs fed 2.50% MM had a more (P < .10) intense color (as indicated by a higher saturation index) than the LM from pigs fed the control diets. Experiment 2. Dietary MM had no (P > .10) effect on ADG, ADFI, G:F, or live weight during the starter, grower, or finisher phases (Table 5). During the entire feeding period (27.2 to 106.8 kg), ADG, ADFI, and G:F were unaffected (P > .10) by supplementing growingfinishing diets with MM. Carcass characteristics of swine fed 0, 1.25, and 2.50% MM are reported in Table 6. Carcasses from
Table 2. Effect of magnesium mica level on performance of growing-finishing swine (Exp. 1) Magnesium mica, % 0
1.25
2.50
SE
La
Qa
Starter (24.1 − 34.5 kg) ADG, g ADFI, g Gain:feed ratio
637.0 1,439.5 .447
625.8 1,456.6 .431
618.6 1,407.0 .444
25.49 71.16 .0231
.617 .752 .932
.950 .708 .622
Grower (34.5 − 66.0 kg) ADG, g ADFI, g Gain:feed ratio
974.0 2,440.4 .399
968.6 2,362.2 .411
956.6 2,378.9 .403
29.03 55.25 .0072
.678 .445 .711
.927 .495 .291
Finisher (66.0 − 102.3 kg) ADG, g ADFI, g Gain:feed ratio
948.2 3,035.4 .313
986.1 3,103.2 .318
938.8 3,018.5 .311
18.34 48.43 .0055
.722 .808 .727
.079 .219 .419
Overall (24.1 − 102.3 kg) ADG, g ADFI, g Gain:feed ratio
900.2 2,527.3 .356
908.6 2,499.2 .364
891.5 2,500.3 .357
14.49 43.93 .0048
.676 .670 .940
.485 .791 .248
24.28 34.75 66.31 105.56
24.23 34.59 66.61 108.00
24.25 34.74 65.81 104.53
.021 .346 .990 1.146
.380 .982 .723 .537
.292 .723 .658 .054
Item
Weights, kg Initial Starter phase Grower phase Finisher phase a
P-value for linear (L) and quadratic (Q) effects of supplemental magnesium mica.
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Table 3. Effect of magnesium mica level on carcass traits (Exp. 1) Magnesium mica, % Item Hot carcass weight, kg Dressing percentage, % Average backfat thickness, cm Tenth rib fat depth, cm Longissimus muscle area, cm2 Percentage muscle, %b Marbling scorec American color scored Japanese color scoree CIE L*f CIE a*f CIE b*f Hue angleg Saturation indexh
0
.25
2.50
SE
La
Qa
77.8 73.67 2.67 2.32 30.6 49.07 2.19 1.95i 2.73 55.95 8.42i 17.76 64.73 19.67k
79.4 73.41 2.74 2.28 30.1 48.91 2.28 2.14j 3.03 55.40 9.01j 18.05 63.57 20.19kl
76.8 73.42 2.69 2.07 29.8 50.29 1.90 2.23j 2.93 55.27 9.05j 18.11 63.55 20.26l
1.01 .383 .048 .079 .75 .591 .161 .064 .113 .382 .143 .174 .359 .188
.500 .646 .829 .072 .460 .237 .227 .009 .233 .228 .008 .185 .035 .044
.117 .785 .357 .467 .919 .375 .260 .536 .172 .659 .143 .592 .219 .341
a
P-values for linear (L) and quadratic (Q) effects of supplemental magnesium mica. Percentage muscle = ([7.231 + (.437 × hot carcass wt, lb.) − (18.746 × 10th rib fat depth, in.) + (3.877 × longissimus muscle area, in.2)] ÷ hot carcass wt) × 100 (NPPC, 1991). c 1 = devoid to practically devoid; 2 = traces to slight; 3 = small to modest; 4 = moderate to slightly abundant; and 5 = moderately abundant or greater. d 1 = pale pinkish gray; 2 = grayish pink; 3 = reddish pink; 4 = purplish red; and 5 = dark purplish red. e 1 = pale gray and 6 = dark purple (Nakai et al., 1975). f L* = measure of lightness to darkness (larger number indicates a lighter color); a* = measure of redness (larger number indicates a more intense red color); and b* = measure of yellowness (larger number indicates more yellow color). g Hue angle represents a change from red to yellow color (larger number indicates a “lighter” red). h Saturation index is a measure of total color or chroma (larger number indicates more vivid color). i,j Within a row, means lacking a common superscript letter differ (P < .05). k,l Within a row, means lacking a common superscript letter differ (P < .10). b
pigs fed 1.25% MM had less (P < .05) fat opposite the LM at the 10th rib than carcasses from untreated controls and pigs fed 2.50% MM. Although hot carcass weight and LM depth were unaffected (P > .10) by dietary MM, carcasses of pigs fed 1.25% MM had higher (P < .10) percentages of muscle than carcasses of pigs fed the control diets. Inclusion of MM in the diet had no (P > .10) effect on LM pH, marbling scores, firmness scores, or American and Japanese color scores (Table 6). Longissimus mus-
Table 4. Effect of magnesium mica level on frequency of Americana and Japaneseb color scores (Exp. 1)
cle L* values were not (P > .10) affected by feeding MM; however, the LM from pigs fed 1.25% MM was less (P < .05) red and less (P < .05) yellow (lower a* and b* values, respectively) than the LM from pigs fed the control or the 2.50% MM-supplemented diets. Moreover, there was a quadratic relationship (P < .001) between saturation index (chroma) and MM inclusion in the diet. Chroma values for the LM from pigs fed 1.25% MM were lower (P < .05), indicating a less vivid color, than those for the LM from untreated controls or pigs fed 2.50% MM. Hue angle and drip loss percentage for the LM were not (P > .10) affected by supplemental MM in the diet of growing-finishing swine.
Magnesium mica, %
Discussion
0
1.25
2.50
American color scoresc 1 2 3
15.40 74.36 10.26
5.60 75.00 19.44
2.50 72.50 25.00
Japanese color scoresd 1 2 3 4
12.82 15.38 58.97 12.82
0.0 19.44 58.33 22.22
0.0 30.00 47.50 22.50
a 1 = pale, pinkish gray; 2 = grayish pink; and 3 = reddish pink (NPPC, 1991). b 1 = pale gray and 6 = dark purple (Nakai et al., 1975). c Chi-square statistic = 6.94 (P < .14). d Chi-square statistic = 13.64 (P < .04).
Animal Performance. Supplemental MM in the diets of growing-finishing swine had no appreciable effects on live animal growth performance (Tables 2 and 6). This is consistent with the observations in two feedlot cattle experiments that inclusion of MM had no deleterious, or beneficial, effects on weight gain or feed efficiency (Coffey and Brazle, 1995; Coffey et al., 1995). It is interesting to note that as the level of MM increased in diets of growing-finishing pigs, the ME content decreased almost 2.49%, from an average of 713.8 kcal/kg in the control diets (average ME for starter, grower, and finisher diets) to 696.0 kcal/kg in the diets supplemented with 2.50% MM (Table 1). The lack of
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Table 5. Effect of magnesium mica level on performance of growing-finishing swine (Exp. 2) Magnesium mica, % 0
1.25
2.50
SE
La
Qa
Starter (24.1 − 34.5 kg) ADG, g ADFI, g Gain:feed ratio
617.7 1,486.4 .415
562.9 1,385.1 .407
623.1 1,454.8 .429
36.12 56.78 .0140
.916 .701 .472
.215 .239 .386
Grower (34.5 − 66.0 kg) ADG, g ADFI, g Gain:feed ratio
925.7 2,481.7 .373
909.2 2,353.5 .387
893.7 2,376.8 .376
16.68 50.18 .0046
.197 .161 .663
.980 .238 .053
Finisher (66.0 − 102.3 kg) ADG, g ADFI, g Gain:feed ratio
952.4 2,949.0 .368
978.5 3,085.0 .317
929.8 3,171.4 .298
29.52 198.73 .0409
.598 .442 .249
.319 .920 .762
Overall (24.1 − 102.3 kg) ADG, g ADFI, g Gain:feed ratio
877.9 2,506.3 .360
873.7 2,463.0 .355
855.1 2,522.9 .341
17.26 100.10 .0142
.365 .908 .367
.738 .681 .804
27.22 38.36 69.24 108.86
27.22 37.49 67.92 108.49
27.22 38.30 68.13 106.73
.007 .570 .891 1.605
.848 .934 .395 .365
.825 .250 .498 .738
Item
Weights, kg Initial Starter phase Grower phase Finisher phase a
P-value for linear (L) and quadratic (Q) effects of supplemental magnesium mica.
Table 6. Effect of magnesium mica level on carcass traits (Exp. 2) Magnesium mica, % Item Hot carcass weight, kg Tenth rib fat depth, cm Longissimus muscle depth, cm Percentage muscle, %b Ultimate muscle pH Marbling scorec Firmness scored American color scoree Japanese color scoref CIE L*g CIE a*g CIE bg Hue angleh Saturation indexi Drip loss, %
0
1.25
2.50
SE
La
Qa
80.2 2.56i 5.00 49.20l 5.60 2.17 2.39 2.53 4.13 51.59 7.09j 15.33j 65.31 16.93j 2.27
78.8 2.12k 4.90 50.64m 5.75 2.09 2.19 2.55 4.13 51.82 6.35k 14.65k 66.67 16.00k 2.59
83.2 2.37j 5.26 50.09lm 5.62 1.90 2.48 2.59 4.01 51.57 6.93j 15.19j 65.54 16.72j 2.19
1.24 .065 .113 .426 .053 .119 .121 .098 .053 .482 .174 .140 .551 .167 .313
.128 .091 .180 .186 .830 .142 .616 .660 .158 .977 .519 .504 .775 .379 .857
.087 .001 .129 .084 .048 .706 .122 .959 .404 .690 .008 .004 .086 .001 .357
a
P-values for linear (L) and quadratic (Q) effects of supplemental magnesium mica. Percentage muscle = ((2.827 + (.469 × hot carcass wt, lb.) + 9.824 × [10th rib fat depth, nm × .0393701]) − (18.47 × [LM depth, mm × .0393701])) ÷ hot carcass wt) × 100. c 1 = devoid to practically devoid; 2 = traces to slight; 3 = small to modest; 4 = moderate to slightly abundant; and 5 = moderately abundant or greater. d 1 = very soft; 2 = soft; 3 = slightly firm; 4 = firm; and 5 = very firm. e 1 = pale pinkish gray; 2 = grayish pink; 3 = reddish pink; 4 = purplish red; and 5 = dark purplish red. f 1 = pale gray and 6 = dark purple (Nakai et al., 1975). g L* = measure of lightness to darkness (larger number indicates a lighter color); a* = measure of redness (larger number indicates a more intense red color); and b* = measure of yellowness (larger number indicates more yellow color). h Hue angle represents a change from red to yellow color (larger number indicate a “lighter” red). i Saturation index is a measure of total color or chroma (larger number indicates more vivid color). j,k Within a row, means lacking a common superscript letter differ (P < .05). l,m Within a row, means lacking a common superscript letter differ (P < .10). b
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reduction in ADFI or G:F in pigs fed dietary MM suggests that a small reduction in energy intake may have resulted in improved energy efficiency. The activation of several enzymes in intermediary metabolism by Mg led Heaton (1973) to speculate that increasing extracellular/intracellular Mg concentrations could increase enzyme activity. The result would be increased ATP production from energy substrates and improved energy utilization/efficiency (Heaton, 1973). Carcass Cutability. In Exp. 1, MM supplementation had no effect on measurements of carcass fatness or muscling. In Exp. 2, carcasses from pigs fed 1.25% MM had less fat opposite the LM at the 10th rib and higher percentage muscle than carcasses from pigs fed either the control diet or the control diet supplemented with 2.50% MM (Table 6). Kuhn et al. (1981) reported that carcasses from pigs fed Mg carbonate for 100 d prior to slaughter were leaner and yielded a greater quantity of lean pork. Additionally, Apple et al. (1999) reported that intramuscular lipid content in the LM was reduced in lambs fed MM for an extended period of time. Conversely, neither Schaefer et al. (1993) nor D’Souza et al. (1998, 1999) noted an effect of supplemental Mg on fat or muscle measurements, but these authors fed supplemental Mg for only 5 d prior to slaughter. Evidence is available suggesting that increasing circulating Mg levels may indirectly affect lipid deposition. Plasma Mg status has no direct effects on the activity of lipolytic enzymes (Rayssiguier et al., 1991) or lipogenic enzymes (Nassir et al., 1995). However, hypermagnesemia has been shown to inhibit insulin secretion and retard glucose assimilation into lipids (Zˇ ofkova´ et al., 1988). Additionally, hypomagnesemia, or consumption of Mg-deficient diets, consistently elicits increased serum triglyceride and cholesterol concentrations (Rayssiguier et al., 1981; Gueux and Rayssiguier, 1983; Luthringer et al., 1988). Subsequent increases in serum Mg dramatically reduced plasma lipid content by increasing disposal of lipids, but not into fatty acid depots (Ouchi et al., 1990; Haenni et al., 1998). Flink et al. (1980) reported that circulating free fatty acids chelated with Mg, forming “soaps” that would be cleared from the blood into the feces. Thus, supplemental Mg could indirectly interrupt lipogenesis by reducing the pool of free fatty acids available for lipid biosynthesis. Pork Quality. In Exp. 1, improvements in pork quality were evident in carcasses from pigs fed diets supplemented with MM (Table 3). An important observation was that the LM color, subjectively and objectively measured, was improved by supplementing the growing-finishing diets of pigs with MM. The LM of carcasses from pigs fed 1.25 and 2.50% MM received higher American color scores than LM from pigs fed the control diet. The effect of MM on pork quality could be attributed to the decrease in the percentage of carcasses receiving undesirable color scores of 1 (characteristic of PSE pork) and an increase in the
Table 7. Effect of magnesium mica level on frequency of Americana and Japaneseb color scores (Exp. 2) Magnesium mica, % 0
1.25
2.50
American color scores 2 3
70.37 29.63
65.38 34.62
76.19 23.81
Japanese color scoresd 3 4 5
7.41 88.89 3.70
3.85 96.15 0.0
9.52 90.48 0.0
c
2 = grayish pink and 3 = reddish pink (NPPC, 1991). 1 = pale gray and 6 = dark purple (Nakai et al., 1975). Chi-square statistic = .65 (P < .72). d Chi-square statistic = 2.40 (P < .66). a b c
percentage of carcasses receiving desirable American and Japanese scores of 3 and 4, respectively (Table 4). However, improvements in subjective or objective measurements of pork color were not as evident in Exp. 2 (Tables 6 and 7). Moreover, inclusion of MM in diets of growing-finishing swine had no effect on drip loss percentages. Our results conflict with those of Schaefer et al. (1993) and D’Souza et al. (1998, 1999), who reported that supplementing finishing diets with Mg aspartate dramatically reduced moisture loss from the LM. The inconsistency of results from Exp. 1 and Exp. 2 may be attributed to differences in the genetics of pigs used in each experiment. Although no laboratory tests were conducted to confirm halothane status, pigs in Exp. 1 were generated from Yorkshire and Yorkshire-cross females known to be homozygous or heterozygous carriers of the halothane gene. In the year between experiments, a concerted effort was made to eliminate all breeding stock that were carriers of the halothane gene, and the University of Arkansas Swine Research Center used sire lines known to be halothane-negative. This was evident by the finding that no carcasses received an undesirable American or Japanese color score of 1 (Table 7), which would be characteristic of PSE pork. Therefore, the population of swine in Exp. 2 was stress-resistant, and these pigs may have been less responsive to the inclusion of MM in the diets. Previous research implies that the magnitude of responses to Mg treatment on pork quality may to be related to the stress susceptibility, or resistance, of pigs in the experiment. Campion et al. (1971) reported that initial and ultimate muscle pH was higher in stress-susceptible pigs intravenously infused with Mg chloride immediately prior to slaughter, but muscle pH was unaffected by Mg infusion in stress-resistant pigs. Similarly, postmortem pH decline and drip loss from the ham, loin, and shoulder was curtailed in Pietrain and Landrace pigs, but not Large White pigs, injected with Mg sulfate prior to slaughter (Lister and Ratcliff, 1971). Additionally, Schmitten et al. (1984)
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reported that inclusion of Mg aspartate in the diet of finishing pigs resulted in improvements in pork color and moisture retention in halothane-positive pigs but did not affect pork quality characteristics of halothane-negative pigs. The improvements in pork color and water-holding capacity in response to dietary Mg aspartate reported by Schaefer et al. (1993) were for an experimental population of confirmed heterozygous carriers of the halothane gene. Thus, stress-susceptible pigs (in particular, heterozygous carriers of the halothane gene) may benefit the most from the supplementary Mg. Pork quality has been shown to be improved by inclusion of Mg aspartate, Mg aspartate hydrochloride, and Mg fumarate in swine finishing diets (Otten et al., 1992; Schaefer et al., 1993; D’Souza et al., 1998, 1999). However, these chelated, organic sources of Mg are quite expensive (D’Souza et al., 1999). Although antemortem injections of Mg chloride and Mg sulfate effectively increased muscle pH and water-holding capacity, little information is available detailing the effect of feeding less-expensive, inorganic sources of Mg on pork quality. Results from this study confirm that inclusion of MM, a cheap inorganic Mg source, in the diets of growing-finishing swine has beneficial effects on pork carcass cutability and quality with no deleterious effects on live animal performance.
Implications Magnesium mica is an inexpensive source of magnesium that can be included in the starter, grower, and finisher diets of pigs to reduce feed costs without affecting live animal performance. Although results of the two experiments differed, it can be suggested that dietary inclusion of magnesium mica at a level of 1.25 or 2.50% may improve pork color and reduce the incidence of pale, soft, and exudative carcasses in populations predisposed to this defect. Moreover, supplementing the diets of growing-finishing swine with magnesium mica may also have beneficial effects on fat depth and lean muscle yields.
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