J. Anim. Sci. 2006. 84:185-190
© 2006 American Society of Animal Science
Effects of supplemental magnesium concentration of drinking water on pork quality1
B. R. Frederick2,
E. van Heugten3,
D. J. Hanson4 and
M. T. See
Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695-7621
 |
Abstract
|
|---|
Thirty-two barrows were used to determine the effects of supplemental Mg in drinking water on pork quality. Pigs were determined to be free of the halothane and Napole mutations and were individually penned. After a 7-d adjustment period, barrows (111 ± 1 kg BW) were blocked by BW and allotted randomly within block to 0, 300, 600, or 900 mg of supplemental Mg from Mg sulfate/L of drinking water for 2 d before slaughter. Pigs were not allowed access to feed (0.13% Mg) for 15 h before slaughter but continued to have access to experimental water treatments. Pigs were loaded and transported 110 km (1.75 h) to a commercial abattoir and remained in lairage for 5 h before slaughter. The LM was removed 24 h postmortem. Retail storage was simulated for 8 d, and the remaining LM was vacuum-packaged for 25 or 50 d at 4°C. Plasma Mg concentration increased linearly (P = 0.001) with Mg supplementation; however, Mg concentration of the LM was not affected (P = 0.99) by Mg supplementation. Surface exudate, drip loss, and retail fluid loss of the LM were not affected (P > 0.10) by Mg. Lightness (L*) and redness (a*) of the LM were not affected (P > 0.10) by Mg, with the exception of initial redness (cubic; P = 0.05). Pigs supplemented with 300 or 900 mg of Mg/L had lower yellowness (b*) values of the LM displayed for 0 to 6 d than pigs supplemented with 0 or 600 mg of Mg/L (cubic; P < 0.05). Lightness of the LM after 25 (quadratic; P = 0.03) or 50 (quadratic; P = 0.04) d of vacuum-packed storage was greater at 300 and 600 mg of Mg/L than at 0 or 900 mg/L. Yellowness tended to be greater after 50 d, but not after 25 d, of vacuum-packaged storage for 300 or 600 mg of Mg/L compared with 0 or 900 mg/L (quadratic; P = 0.08). Oxidation of the LM, determined by thiobarbituric acid reactive substances after 4 d of retail storage, increased linearly (P = 0.05) as Mg increased in the drinking water. Furthermore, oxidation of the LM after 8 d of retail storage tended to increase linearly (P < 0.10), primarily because of the high oxidation of LM from pigs supplemented with 900 mg of Mg/L compared with controls (224 vs. 171 ± 19 µg/kg, respectively). Oxidation of the LM was greater for pigs supplemented with 300 or 900 mg/L compared with 0 or 600 mg of Mg/L (cubic; P < 0.06) after 25 d of vacuum-packed storage. Magnesium did not improve pork quality characteristics of practical significance in pigs without the halothane and Rendement Napole mutations.
Key Words: magnesium • pork • quality • swine • water
|
INTRODUCTION
|
|---|
Dietary Mg is a relatively inexpensive method of improving pork quality because of low-cost sources (such as Mg sulfate) and short duration of supplementation (D’Souza et al., 2000
; Hamilton et al., 2002; van Heugten and Frederick, 2004). Loins from pigs supplemented with Mg before slaughter have been reported to have greater ultimate pH (D’Souza et al., 1998; Caine et al., 2000; Swigert et al., 2004), improved color (D’Souza et al., 1998; Apple et al., 2000; Geesink et al., 2004), less drip loss (D’Souza et al., 1998, 1999; Caine et al., 2000), and less lipid oxidation (Apple et al., 2001) than nonsupplemented pigs.
The most consistent response to date has been observed in pigs that were stressed before slaughter by multiple electric shocks (D’Souza et al., 1998, 1999) or slaughtered after transport without lairage (Geesink et al., 2004). Indeed, Mg has been shown to decrease the acute stress response resulting from handling before slaughter (Kietzmann and Jablonski, 1985), control intracellular Ca (Laver et al., 1997), and delay the initiation of glycolysis by maintaining high-energy phosphates postmortem (Moesgaard et al., 1993).
Although dietary supplementation of Mg before slaughter has been modestly effective, the short period required to elicit a response may limit the practical aspects of delivery via feed because of feed withdrawal before slaughter and logistics of implementation in production conditions. Water supplementation of Mg, however, is relatively simple to implement, and it can be applied for any time period before transport.
The most effective duration of Mg supplementation via drinking water was determined to be 2 d before slaughter (Frederick et al., 2004); however, the dose of Mg during the supplementation period may affect pork quality (Schaefer et al., 1993; D’Souza et al., 2000). Therefore, the objective of this study was to determine the optimum supplemental Mg concentration of drinking water to improve pork quality.
|
MATERIALS AND METHODS
|
|---|
Animals and Treatments
All animal procedures were approved by the Institutional Animal Care and Use Committee of North Carolina State University. Thirty-two barrows (Landrace x Yorkshire) weighing 111.0 ± 1.0 kg from the North Carolina State University Swine Education Unit previously determined to be free of the halothane and Rendement Napole mutations on Chromosomes 6 and 15, respectively, by DNA testing (GeneSeek, Lincoln, NE) were placed into 2.03-m x 0.74-m individual pens and were provided free access to water via a nipple waterer. Pigs had ad libitum access to feed containing 0.13% Mg (as-fed basis) from feedstuffs (Table 1) during a 7-d adjustment and 2-d treatment period. After the adjustment period, pigs were blocked by BW and allotted to water supplemented with 0, 300, 600, or 900 mg of elemental Mg from magnesium sulfate heptahydrate/L (9.8% Mg; Giles Chemical Corp., Waynesville, NC) for 2 d before slaughter. Plastic water containers (23-L capacity) were filled daily with 15 L of water containing the appropriate Mg concentration. These containers were suspended from the ceiling and gravimetrically emptied into a galvanized pipe leading to a nipple waterer regulated to dispense 600 mL of water/min. Daily water disappearance volumes were determined by weight loss of the water containers, assuming that 1 kg equaled 1 L of water. Feed was removed 15 h before transport to the abattoir; however, pigs had free access to experimental water treatments until loading time.
Slaughter, Fabrication, and Storage
On d 10 (at 0900), all pigs were loaded and transported 110 km (1.75 h) to a commercial abattoir. Pigs were unloaded by abattoir personnel. After 5 h of lairage, pigs were moved, by replicate, 50 m to the stunning area. Pigs were electrically stunned, and blood was collected during exsanguination for determination of plasma Mg concentration. Hot carcass weights were collected before chilling to calculate dressing percent. The temperature and pH of the loin were measured between the 10th and 11th ribs at 45 min and 24 h postmortem using an Argus Sentron (Gig Harbor, WA) pH meter.
After 20 h of chilling at 2°C, the entire bone-in loin from the right side was removed and transported 60 km (45 min) at 4°C to a commercial meat fabrication facility for further processing. A total of four 2.54-cm-thick LM chops were obtained, beginning at the 7th and 8th rib interface. The first chop was used for drip loss determination on the same day of collection. The second chop was obtained immediately posterior to the first, placed in a plastic bag, and frozen at –20°C for determination of initial oxidation, DM, and tissue Mg concentration. The third chop was obtained immediately posterior to the second chop, placed on an absorbent pad (Cryovac Sealed Air Corp., Saddle Brook, NY) on a Styrofoam tray (Cryovac Sealed Air Corp.), wrapped with a PVC film (Cryovac Sealed Air Corp.), and stored at 4°C in the presence of fluorescent lighting to simulate retail display for 4 d. The fourth chop was taken immediately posterior to the third chop and was stored in a similar environment as the third chop for 8 d of retail storage. The retail packages were stored in a random fashion on 2 tables in a walk-in refrigerator at 4°C, approximately 1.5 m below 2 shop lights (1.22 m in length) containing 2 fluorescent lights each (40-W, F40CW-EX, General Electric Co., Cleveland, OH) to simulate retail display. At the end of the retail storage period, chops were analyzed for extent of oxidation. The remaining posterior portion of the LM was divided into 2 equal sections, weighed, vacuum-packed in B2651T Cryovac bags with a Mulitvac machine (Cryovac, Duncan, SC), and stored at 4°C in the absence of light for 25 or 50 d.
Pork Quality Measurements
Surface exudate was measured with filter paper on a freshly cut surface according to the procedures of Kauffman et al. (1986). Drip loss (Honikel et al., 1986) was determined on a fresh chop as the fluid loss of a 70-g core sample suspended by a fish hook in a plastic, covered container at 4°C for 48 h. Retail fluid loss was determined on d 4 and 8 on chops designated for 8 d of retail storage as previously described by Frederick et al. (2004). Objective color (L*, a*, and b*) measurements were collected with a Minolta Chroma Meter (CR-200, Minolta Corp., Ramsey, NJ) and calibrated with a standard white plate using D65 illuminant every 2 d on chops designated for 8 d of retail storage and on d 25 and 50 on an interior chop from vacuum-packaged LM. Chops displayed for 4 or 8 d, as well as LM chops from vacuum-packaged loin sections displayed for 25 or 50 d, were vacuum-packaged in Cryovac bags (Bag No. B2651T) and stored at –20°C until oxidation was determined by thiobarbituric acid-reactive substances (TBARS).
Chemical Analyses
Plasma and muscle Mg concentrations were determined in duplicate by atomic absorption spectrophotometry after samples were digested with nitric acid and hydrogen peroxide (Frederick et al., 2004). Oxidation in muscle was determined by TBARS, as described by Witte et al. (1970), using tetraethoxypropane as a standard. Reported TBARS values were corrected for percent recovery, which was determined in concurrent duplicate meat samples to which 1 mL of 80 x 10–7 M tetraethoxypropane was added before homogenation (Frederick et al., 2004). Recovery ranged from 94 to 101%.
Statistical Analyses
Data were analyzed as a randomized complete block design using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Pig within individual pen was considered the experimental unit. The model included block and Mg treatment. Linear, quadratic, and cubic contrasts were used to partition the effects of Mg supplementation. Least squares means were reported, and differences were considered significant at P < 0.05, whereas tendencies were reported at 0.05 < P < 0.10.
|
RESULTS AND DISCUSSION
|
|---|
Feed intake and water disappearance were not (P > 0.10) affected by Mg supplementation (Table 2). Water used to mix the Mg contained 3 mg of Mg/L; therefore, the mean maximum intake of Mg from drinking water was 0.04, 3.27, 6.27, and 10.57 g/d for Mg concentrations of 0, 300, 600, and 900 mg/L, respectively; however, the actual intake might have been lower because waste water was not measured. Cumby (1986) reported an estimated water requirement of 2 L/kg of feed, which would result in a predicted Mg intake ranging from 2.1 to 5.7 g/d for pigs supplemented with Mg. D’Souza et al. (1998, 1999, 2000) reported improvements in pork quality when feeding 1.6 or 3.2 g of elemental Mg from sources including Mg aspartate, chloride, or sulfate for 2 to 5 d.
View this table:
[in this window]
[in a new window]
|
Table 2. Effect of supplemental Mg concentration in drinking water on measurements taken at the time of slaughter1
|
|
Although plasma Mg measured at time of slaughter increased linearly (P = 0.001) as Mg concentration in drinking water increased, Mg concentration of the LM was unchanged (P > 0.10; Table 2
) by treatment. Therefore, any effects associated with Mg supplementation did not seem to be a result of accumulation of Mg in muscle. Schaefer et al. (1993) reported that plasma Mg increased 34% when pigs were supplemented with 25.2 mg of Mg/d (calculated from their supplementation rate of 20 g of Mg aspartate product as a top dress/d, containing 1.3% Mg aspartate, which contained 9.7% elemental Mg) for 5 d. Moreover, Mg concentration of skeletal muscle, liver, and heart tissue did not change with Mg supplementation in the study of Schaefer et al. (1993).
The initial pH of the LM tended to decrease quadratically (P = 0.09) with increasing levels of Mg; loins from pigs fed 600 ppm of Mg/L reached the lowest pH (Table 2). However, the pH of the LM at 24 h decreased linearly (P = 0.05) as Mg concentration increased in the drinking water. This result suggests that the rate and the extent of pH decline after 45 min postmortem was increased by Mg supplementation. These results contradict results reported by D’Souza et al. (1998) and Swigert et al. (2004), who reported a greater ultimate pH with Mg supplementation, and D’Souza et al. (1999, 2000) and Hamilton et al. (2002), who reported no differences in ultimate pH between Mg and nonsupplemented pigs. Postmortem pH is often used as a predictor of pork quality (NPPC, 2001); an initial pH of 6.3 to 6.7 and an ultimate pH of 5.7 to 6.1 is optimal. The initial pH values observed in the present study were relatively low, indicating a rapid pH decline postmortem and possible development of PSE pork. On the other hand, ultimate pH values were relatively high, especially for control pigs, which would be more closely related to the DFD condition. It is not clear why initial pH was lower than ultimate pH in pigs fed 0, 300, or 600 mg of Mg/L; however, because of the large variation in pH measurements, values were not different. Ultimate pH values were in the normal range; therefore, the practical relevance of the decrease in ultimate pH when Mg was supplemented may be limited.
Fluid loss measured by surface exudate, drip loss, and retail fluid loss were not (P > 0.10) affected by Mg supplementation (Table 3). These results are in agreement with those of Caine et al. (2000), who reported no effects on drip loss of Mg supplementation from Mg aspartate at either 5 mg/kg of BW for 43 d or 40 mg/kg of BW for 7 d. In contrast, D’Souza et al. (1998, 1999, 2000) consistently showed decreased drip loss when Mg from Mg aspartate, Mg sulfate, or Mg chloride was supplemented at 1.6 or 3.2 mg/d for 2 to 5 d. Schaefer et al. (1993) reported that 40.4 mg of Mg from Mg aspartate as a top dress for 5 d decreased drip loss in LM from pigs with the halothane mutation; however, a reported 25.2 mg of Mg from Mg aspartate daily for 5 d did not affect drip loss in that experiment (Schaefer et al., 1993). Apple et al. (2000, 2001) reported no effect on drip loss of feeding 1.25 or 2.5% Mg mica (containing 8% Mg) during the starter to finisher phase of production.
View this table:
[in this window]
[in a new window]
|
Table 3. Effect of supplemental Mg concentration in drinking water on fluid loss of pork displayed for 2, 4, 6, and 8 d1
|
|
Lightness (L*) and redness (a*) values were not (P > 0.10) affected by Mg supplementation, with the exception of a cubic response (P = 0.05) of Mg on initial redness (Table 4). However, the LM of pigs supplemented with 300 or 900 mg of Mg/L was less yellow (b* values) than the LM of pigs supplemented with 0 or 600 mg of Mg/L during the first 6 d of simulated retail display (cubic; P < 0.05). The L* values observed in the present experiment were very high, indicating extreme PSE (NPPC, 2001); however, visual observations throughout this experiment would classify the loin chops obtained from these pigs as normal. Thus, we do not have a clear explanation why the absolute L* values were this high. As expected, L* values increased and a* values decreased in all treatment groups as the display time increased from 0 to 8 d, which indicated that relative comparisons between treatment groups and display periods were valid.
View this table:
[in this window]
[in a new window]
|
Table 4. Effect of supplemental Mg concentration in drinking water on pork color during 8 d of simulated retail display1
|
|
Magnesium concentration in drinking water had a quadratic effect on lightness (L* values) of the LM after 25 (P = 0.03) or 50 d (P = 0.04) of vacuum-packaged storage, indicating 300 and 600 mg of supplemental Mg/L increased L* values compared with pigs supplemented with 0 or 900 mg of Mg/L (Table 5). Yellowness tended to be greater after 50 d of refrigerated, vacuum-packaged storage for pigs that had been supplemented with 300 or 600 mg of Mg/L compared with those receiving 0 or 900 mg/L (quadratic; P = 0.08), but not (P > 0.10) after 25 d of vacuum-packaged storage. The inconsistent effects on yellowness (b* value) associated with different supplemental Mg intakes have been reported previously (Apple et al., 2000, 2001); however, others reported no effects of Mg supplementation on pork color (D’Souza et al., 1999; Caine et al., 2000) or only decreased L* values (D’Souza et al., 1998, 2000; Hamilton et al., 2002). Geesink et al. (2004) observed decreased lightness and increased redness in LM of pigs supplemented with 1.19 g of Mg from Mg acetate for 5 d when they had not been held in lairage before slaughter, but reported no effects in pigs held in lairage for 2 h.
View this table:
[in this window]
[in a new window]
|
Table 5. Effect of supplemental Mg concentration in drinking water on LM color after refrigerated vacuum-packaged storage1
|
|
Oxidation of the LM, determined by TBARS values after 4 d of simulated retail storage display, increased linearly (P = 0.05) as Mg concentration in drinking water increased (Table 6). Furthermore, oxidation of the LM after 8 d of retail storage tended to increase linearly (P = 0.10), primarily because of the high oxidation of the LM from pigs supplemented with 900 mg of Mg/L compared with the control (224 vs. 171 ± 19 µg/kg, respectively). Oxidation of the vacuum-packaged LM on d 25 was greater for pigs supplemented with 300 or 900 mg/L than for those supplemented with 0 or 600 mg of Mg/L (cubic; P = 0.06). Previous results indicated that supplementation of 900 ppm of Mg via water for 2 d decreased the extent of oxidation in the LM after display storage and that increasing the duration of supplementation from 2 to 8 d incrementally increased oxidation to levels similar to that of the control treatment (Frederick et al., 2004). An inconsistent effect on oxidation was observed by Apple et al. (2001), who reported that 1.25% Mg mica in the starter, grower, and finisher diets increased oxidation after 28 d of vacuum-packed storage compared with pigs fed 2.5% Mg mica. Conversely, the oxidation of pork was greater after 56 d of vacuum-packed storage from pigs fed 2.5% Mg mica than that from pigs fed 1.25% Mg mica in the same study.
|
IMPLICATIONS
|
|---|
Although magnesium supplementation through drinking water has improved pork quality in previous experiments, the effect of magnesium is not consistent. Genetic differences and stress associated with handling and transit, along with lairage time before slaughter, may be reasons for variable results across studies. Nevertheless, magnesium supplementation at high concentrations may decrease pork quality by increasing oxidation, which could result in a shorter shelf life. Future research should focus on establishing the conditions in which a consistent effect of magnesium on pork quality may be expected.
|
Footnotes
|
|---|
1 Appreciation is expressed to The Pork Company (Warsaw, NC), Parks Family Meats (Harrells, NC), and the North Carolina State Univ. Dept. of Food Sci. for facility use and to O. Phillips, S. Wolford, D. Lee, and B. Belstra for technical support. Funded in part by the North Carolina Pork Council, the North Carolina Agric. Res. Service, and the Inst. of Nutr. of the Univ. of North Carolina System. The use of trade names does not imply endorsement by the North Carolina Agric. Res. Service of the products named or criticism of similar ones not mentioned. 
2 Current address: Christensen Family Farms, Sleepy Eye, MN 56085.
4 Dept. of Food Sci., North Carolina State Univ., Raleigh.
3 Corresponding author: Eric_vanHeugten{at}ncsu.edu
Received for publication December 21, 2004.
Accepted for publication July 6, 2005.
|
LITERATURE CITED
|
|---|
Apple, J. K., J. R. Davis, L. K. Rakes, C. V. Maxwell, M. R. Stivarius, and F. W. Pohlman. 2001. Effects of dietary magnesium and duration of refrigerated storage on the quality of vacuum-packaged, boneless pork loins. Meat Sci. 57:43–53.
Apple, J. K., C. V. Maxwell, B. deRodas, H. B. Watson, and Z. B. Johnson. 2000. Effect of magnesium mica on performance and carcass quality of growing-finishing swine. J. Anim. Sci. 78:2135–2143.[Abstract/Free Full Text]
Caine, W. R., A. L. Schaefer, J. L. Aalhus, and M. R. Dugan. 2000. Behaviour, growth performance and pork quality of pigs differing in porcine stress syndrome genotype receiving dietary magnesium aspartate hydrochloride. Can. J. Anim. Sci. 80:175–182.
Cumby, T. R. 1986. Design requirements of liquid feeding systems for pigs: A review. J. Agric. Eng. Res. 34:153–172.
D’Souza, D. N., R. D. Warner, F. R. Dunshea, and B. J. Leury. 1999. Comparison of different dietary magnesium supplements on pork quality. Meat Sci. 51:221–225.
D’Souza, D. N., R. D. Warner, B. J. Leury, and F. R. Dunshea. 1998. The effect of dietary magnesium aspartate supplementation on pork quality. J. Anim. Sci. 76:104–109.[Abstract/Free Full Text]
D’Souza, D. N., R. D. Warner, B. J. Leury, and F. R. Dunshea. 2000. The influence of dietary magnesium supplement type, supplementation dose and duration, on pork quality and the incidence of PSE pork. Aust. J. Agric. Res. 51:185–189.
Frederick, B. R., E. van Heugten, and M. T. See. 2004. Timing of magnesium supplementation administered through drinking water to improve fresh and stored pork quality. J. Anim. Sci. 82:1454–1460.[Abstract/Free Full Text]
Geesink, G. H., R. G. C van Buren, B. Savenije, M. W. A. Verstegen, B. J. Ducro, J. P. G. van der Palen, and G. Hemke. 2004. Short-term feeding strategies and pork quality. Meat Sci. 67:1–6.
Hamilton, D. N., M. Ellis, M. D. Hemann, F. K. McKeith, K. D. Miller, and K. W. Purser. 2002. The impact of longissimus glycolytic potential and short-term feeding of magnesium sulfate heptahydrate before slaughter on carcass characteristics and pork quality. J. Anim. Sci. 80:1586–1592.[Abstract/Free Full Text]
Honikel, D. O., C. J. Kim, P. Roncales, and R. Hamm. 1986. Sacromere shortening of pre-rigor muscles and its influence on drip loss. Meat Sci. 16:267–282.
Kauffman, R. G., G. Eikelenboom, G. P. van der Wal, G. Merkus, and M. Zaar. 1986. The use of filter paper to estimate drip loss of porcine musculature. Meat Sci. 18:191–200.
Kietzmann, M., and H. Jablonski. 1985. Blocking of stress in swine with magnesium aspartate hydrochloride. Prakt. Tierz. 661:331–338.
Laver, D. R., V. J. Owen, P. R. Junankar, N. L. Taske, A. F. Dulhunty, and G. D. Lamb. 1997. Reduced inhibitory effect of Mg2+ on ryanodine receptor-Ca2+ release channels in malignant hyperthermia. Biophys. J. 73:1913–1924.[Abstract/Free Full Text]
Moesgaard, B., I. Errebo Larsen, B. Quistorff, I. Therkelsen, V. G. Christensen, and P. F. Jorgensen. 1993. Effect of dietary magnesium on post-mortem phosphocreatine utilization in skeletal muscle of swine: A non-invasive study using 31P-NMR spectroscopy. Acta Vet. Scand. 34:397–404.[Medline]
NPPC. 2001. Variation in pork lean quality. National Pork Board Fact Sheet. Des Moines, IA.
Schaefer, A. L., A. C. Murray, A. K. W. Tong, S. D. M. Jones, and A. P. Sather. 1993. The effect of ante mortem electrolyte therapy on animal physiology and meat quality in pigs segregating at the halothane gene. Can. J. Anim. Sci. 73:231–240.
Swigert, K. S., F. K. McKeith, T. C. Carr, M. S. Brewer, and M. Culbertson. 2004. Effects of vitamin D3, vitamin E, and magnesium supplementation on pork quality. Meat Sci. 67:81–86.
van Heugten, E., and B. R. Frederick. 2004. Magnesium supplementation and pork quality. Pig News Info. 25:101N–109N.
Witte, V. C., G. F. Krause, and M. E. Bailey. 1970. A new extraction method for determining 2-thiobarbituric acid values of pork and beef during storage. J. Food Sci. 35:582–585.
Top
Abstract
INTRODUCTION
