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Effects of dietary magnesium and halothane genotype on performance and carcass traits of growing-finishing swine
Livestock Production Science 76 (2002) 103–113 www.elsevier.com / locate / livprodsci
Effects of dietary magnesium and halothane genotype on performance and carcass traits of growing-finishing swine Jason K. Apple*, Charles V. Maxwell, Matthew R. Stivarius, Lilly K. Rakes, Zelpha B. Johnson Department of Animal Science, B103 C AFLS Administration Building, University of Arkansas, Fayetteville, AR 72701, USA Received 25 April 2001; received in revised form 31 December 2001; accepted 31 December 2001
Abstract Halothane-negative (NN) and halothane-carrier (Nn) pigs were assigned randomly to one of three dietary treatments: (1) control corn–soybean meal diets; (2) control diets supplemented with 1.25% magnesium mica (MM); or (3) control diets supplemented with 2.5% MM. When the lightest block averaged 108.8 kg, pigs were harvested at a commercial pork slaughter plant, and bone-in pork loins were captured, vacuum-packaged and transported back for measurement of pork quality traits. The NN pigs had greater average daily gain (ADG) during the grower (P , 0.05) and finisher (P , 0.05) periods than Nn pigs. Although MM had no effect (P . 0.10) on ADG, pigs fed 1.25% MM had a higher (P , 0.05) gain-to-feed ratio (G:F) during the grower phase than pigs fed 2.5% MM; whereas, pigs fed control diets had an intermediate G:F. Carcasses from Nn pigs were leaner (P , 0.05) and heavier (P , 0.05) muscled than carcasses from NN pigs. In contrast, a greater (P , 0.05) percentage of carcasses from Nn pigs received color scores characteristic of the pale, soft and exudative (PSE) condition. Although there were distinct genotype effects on performance and carcass traits, long-term supplementation of diets with MM had no beneficial, or deleterious, effects on pork quality or carcass yield. 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnesium; Genotype; Pig-feeding and nutrition; Carcass composition; Pork quality
1. Introduction The incorporation of supplemental magnesium (Mg) into animal diets has traditionally been used to prevent the metabolic disorders associated with Mg deficiency (Littledike et al., 1983). However, research has shown that supplementing swine diets with Mg reduced the stress responses in pigs *Corresponding author. Tel.: 1 1-479-575-4840; fax: 1 1-479575-7294. E-mail address: [email protected] (J.K. Apple).
(D’Souza et al., 1998), producing visibly calmer pigs after long-distance transportation (Kuhn et al., 1981). Moreover, dietary inclusion of Mg has been reported to have beneficial effects on pork quality traits (D’Souza et al., 1998, 1999, 2000; Hemann et al., 2000; Otten et al., 1992), and reducing the incidence of pale, soft and exudative (PSE) pork (D’Souza et al., 1998; Schaefer et al., 1993). The magnitude of responses to supplemental Mg on pork quality traits appears to be related to the stress-susceptibility, or resistance, of the pigs being studied. Campion et al. (1971) reported that muscle
0301-6226 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 02 )00004-0
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J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
pH was higher in stress-susceptible pigs intravenously infused with Mg chloride prior to harvest, but muscle pH was not affected by Mg-infusion in stress-resistant pigs. Likewise, Schmitten et al. (1984) reported that supplementing swine diets for 5 days before harvest with Mg aspartate resulted in improvements in pork color and moisture retention in halothane-positive pigs, but not in halothane-negative pigs. Moreover, the improvements in pork quality in response to short-term supplementation of Mg aspartate reported by Schaefer et al. (1993) were for only confirmed heterozygous carriers of the halothane gene. Muscle drip loss percentages were also reduced when pigs, heterozygous for the rendement napole (RN) gene, were fed diets containing Mg sulfate for 3 to 5 days prior to harvest, but no appreciable effect of dietary Mg was noted in pigs homozygous negative for this gene (Hemann et al., 2000). Magnesium mica (MM) is an inorganic, layered silicate product, containing approximately 8% Mg, that has been used primarily as a pellet binder in the feed milling industry. When incorporated in high concentrate diets of beef cattle, dietary MM was found to increase longissimus thoracis marbling scores and beef quality grades (Coffey and Brazle, 1995). In the first of two experiments from our laboratory (Apple et al., 2000), long-term supplementation of swine diets with MM improved pork color and reduced the proportion of carcasses with quality traits characteristic of PSE pork; however, in the second experiment, dietary MM had no appreciable effects on any pork quality trait measured. Diets for both experiments were identical, but pig populations had changed from a herd of unknown halothane-genotype to an almost exclusively halothane-negative herd in the year between experiments. Therefore, the aim of this experiment was to test the effects of feeding MM during the growingfinishing period on the performance and pork quality traits of halothane-carrier and homozygous-negative pigs.
2. Materials and methods
2.1. Animals and diets Prior to breeding, hair samples from a population
(n 5 30) of Yorkshire 3 Landrace females were collected, packaged, and shipped to Pig Improvement Company headquarters in Franklin, KY, where hairsamples were analyzed for halothane-genotype by their laboratory. All females that were homozygous dominant (NN), or negative, for the halothane-gene were selected and mated to either Duroc 3 Hampshire males (Line TT, The Pork Group, Rogers, AR), tested and guaranteed to be homozygous dominant for the halothane-gene, or to synthetic-bred males (Pig Improvement Company), tested and guaranteed to be homozygous recessive (nn) for the halothane-gene. Pigs generated from these matings were either homozygous dominant / negative (NN) or heterozygous (Nn) carriers of the halothane-gene. Halothane-negative (n 5 45) and halothane-carrier (n 5 75) barrows and gilts, with an average initial body weight (BW) of 17.463.2 kg, were moved from the University of Arkansas Nursery to the University of Arkansas Swine Growing-Finishing Facility and blocked by BW into four blocks. Pigs were then allotted randomly to pens (six pens / block) based on sex and litter origin / genotype, with at least one NN pig / pen (15, 13, 11, and six NN-pigs in blocks 1, 2, 3, and 4, respectively), and one of three treatments was assigned randomly to pens (five pigs / pen) within blocks. Pigs were fed ad libitum a three-phase diet with transition from starter to grower when the average block BW was 34.0 kg, and from the grower to finisher when the mean block BW was 68.2 kg. A total of 24 pens were assigned randomly to one of three treatments: (1) a negative control corn–soybean meal starter, grower, and finisher diets devoid of supplemental magnesium; (2) the control starter, grower, and finisher diets supplemented with 1.25% MM (Micro-Lite Inc., Chanute, KS); or (3) the control starter, grower, and finisher diets supplemented with 2.5% MM (Table 1). Within the MM-supplemented diets, MM was added at the expense of corn. All diets were formulated to meet, or exceed, NRC (1998) requirements for growingfinishing swine, and starter, grower, and finisher diets contained 1.10, 0.95, and 0.85% lysine, respectively (Table 1). Individual pig weights were measured weekly, and feed disappearance was recorded during each phase to calculate average daily gain (ADG), average daily feed intake (ADFI), and gainto-feed ratio (G:F).
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Table 1 Composition of experimental diets Ingredient (% dry matter)
Starter diets
Grower diets
Finisher diets
0.00
1.25
2.50
0.00
1.25
2.50
0.00
1.25
2.50
61.78 30.75 4.00 1.55 0.00 0.82 0.50 0.15 0.25 0.13 0.05 0.03
60.28 31.00 4.00 1.55 1.25 0.82 0.50 0.15 0.25 0.13 0.05 0.03
59.10 30.90 4.00 1.60 2.50 0.82 0.50 0.15 0.25 0.13 0.05 0.03
66.98 25.60 4.00 1.65 0.00 0.77 0.50 0.15 0.15 0.13 0.05 0.03
65.73 25.60 4.00 1.65 1.25 0.77 0.50 0.15 0.15 0.13 0.05 0.03
64.30 25.75 4.00 1.70 2.50 0.77 0.50 0.15 0.15 0.13 0.05 0.03
71.12 21.90 4.00 1.45 0.00 0.68 0.50 0.10 0.13 0.05 0.05 0.03
69.87 21.90 4.00 1.45 1.25 0.68 0.50 0.10 0.13 0.05 0.05 0.03
68.62 21.90 4.00 1.50 2.50 0.68 0.50 0.10 0.13 0.05 0.05 0.03
Calculated composition (% dry matter) Crude protein (CP) 20.17 Lysine 1.10 Methionine 0.32 Methionine and cysteine 0.67 Threonine 0.78 Tryptophan 0.24 Magnesium 0.18 Calcium 0.80 Phosphorus 0.65 Metabolizable energy (Mcal / kg) 3.45
20.16 1.10 0.32 0.67 0.78 0.24 0.28 0.80 0.65 3.40
20.01 1.10 0.32 0.67 0.78 0.24 0.38 0.80 0.65 3.36
18.11 0.95 0.29 0.61 0.70 0.21 0.18 0.80 0.65 3.45
18.00 0.95 0.29 0.61 0.70 0.21 0.28 0.80 0.65 3.41
17.95 0.95 0.29 0.61 0.70 0.21 0.38 0.80 0.65 3.36
16.67 0.85 0.27 0.57 0.64 0.19 0.18 0.60 0.60 3.47
16.56 0.85 0.27 0.57 0.64 0.19 0.28 0.60 0.60 3.42
16.45 0.85 0.27 0.57 0.64 0.19 0.38 0.60 0.60 3.38
Corn Soybean meal (48% CP) Animal and vegetable fat Dicalcium phosphate Magnesium mica Calcium carbonate Salt Mineral premix a Vitamin / trace mineral premix b Tylosin-40 Copper sulfate Ethoxyquin
a
Premix consisted of 11.0% Fe, 11.0% Zn, 2.6% Mn, 1.1% Cu, 0.02% I, and 0.02% Se (Nutra Blend Corp., Neosho, MO). Premix consisted of 909,091 IU vitamin A, 136,134 IU vitamin D, 3636 IU vitamin E, 3.6 mg vitamin B12, 364 mg vitamin K, 818 mg riboflavin, 2727 mg D-pantothenic acid, and 4546 mg niacin per kg (Nutra Blend Corp., Neosho, MO). b
2.2. Carcass data collection When the lightest block of pigs averaged 108.8 kg, all pigs were transported approximately 10 h (724 km) to a commercial pork harvest / fabrication plant (Seaboard Farms Inc., Guymon, OK). After a brief 45-min rest period, pigs were harvested according to industry-accepted procedures, and carcasses were chilled rapidly for 1 to 2 h at 2 26 8C, followed by a ‘tempering’ period where temperature was gradually increased from 2 3 to 2 8C. Approximately 24 h post-harvest, fat and longissimus thoracis et lumborum (LM) depths 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 of approximately 7 cm from the midline. Additionally, trained personnel recorded midline backfat measurements opposite the first rib, last rib, and last lumbar vertebra. Carcasses were then fabricated into subpri-
mal cuts according to Institutional Meat Purchasing Specifications (IMPS) for Fresh Pork Products (USDA, 1995). Bone-in pork loins (IMPS [410) were vacuum-packaged in 40 cm 3 100 cm multiply, bone-guard vacuum bags (oxygen transmission rate 5 15 ml / m 2 / 24 h at 23 8C and 1 atm; water transmission rate 5 0.4 g / 645.2 cm 2 / 24 h at 38 8C and 100% relative humidity; Cyrovac Sealed Air Corp., Duncan, SC), boxed, loaded into a refrigerated truck and shipped back to the University of Arkansas Red Meat Abattoir for pork quality measurements.
2.3. Loin fabrication Upon arrival at the abattoir (approximately 48 h after harvest), loins were removed from the vacuumbags, and the pork tenderloin was removed. Then, 7.6 cm of the cranial (blade) portion was removed perpendicular to the length of the loin and discarded.
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Beginning at the cranial end of the loin, two 2.5-cmthick LM chops were cut for color evaluations and two 3.2-cm-thick LM chops were removed for drip loss determinations.
2.4. Pork quality data collection After a 30-min ‘bloom’ period at 4 8C, the 2.5-cmthick LM chops were visually evaluated for marbling (1 5 devoid [1% intramuscular lipid] to 10 5 abundant [10% intramuscular lipid]; NPPC, 1999), firmness (1 5 very soft and watery to 5 5 very firm and dry; NPPC, 1991), and color based on both the American (1 5 pale, pinkish gray to 6 5 dark purplish red; NPPC, 1999) and Japanese color standards (Nakai et al., 1975). The Japanese color standards system is composed of six plastic disks with meatlike texture and appearance developed from objective colorimetry, and scores range from 1 (pale gray) to 6 (dark purple). Commission International de l’Eclairage L*, a*, and b* values were determined from a mean of four random readings (two readings from each of the 2.5-cm-thick LM chops) made with the Hunter MiniScan XE (model 45 / 0-L, Hunter Associates Laboratory, Reston, VA) using illuminant C and a 108 standard observer. The spectrocolorimeter had a 22mm aperture and was calibrated against a standard white tile (No. M04207 with X 5 81.1, Y 5 85.9, and Z 5 91.6; Hunter Associates Laboratory Inc., Reston, VA).
2.5. Drip loss determinations Drip loss, a measure of the water-holding capacity of the LM, was determined according to the suspension procedure described by Apple et al. (2000). Briefly, a 3.2-cm-diameter core was manually removed from each of the 3.2-cm-thick LM chops. Each core was blotted dry on paper towels, core weight was recorded, and the core was suspended on a fish-hook mounted to the lid of a plastic container (46 3 66 3 38 cm deep Dur-X姠 Food Box; Rubbermaid Commercial Products LLC, Winchester, VA). Containers were sealed tightly and stored at 2 8C for 48 h. After the 48-h storage period, each core was removed from its hook, blotted dry with paper
towels, and re-weighed. The loss in weight was divided by the original core, then multiplied by 100 to calculate drip loss percentage.
2.6. Muscle pH and moisture determinations After core removal for drip loss measurements, 2 g of LM were removed, and, subsequently, homogenized in 20 ml of distilled, deionized water. 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., Arvada, CO). Additionally, duplicate samples (approximately 5 g) of LM were weighed, placed in 30-ml beakers, and weighed. Beakers were then placed into vacuum flasks and attached to the manifold of a Labconco freeze-dryer (model 4.5, Labconco Corp., Kansas City, MO) with a temperature setting of 2 50 8C at a vacuum of less than 10 mm of Hg. Samples were freeze-dried for 36 h, and beakers were re-weighed. The difference between the initial and dried beaker weights was divided by the sample weight to calculate the percentage of moisture.
2.7. Statistical analysis All data were analyzed as a split plot design with pen as the experimental unit for performance data and pig as the experimental unit for all carcass data. Analysis of variance was generated using the PROC MIXED procedure (SAS Institute Inc., Cary, NC), with the main effects of genotype and dietary MM, as well as the genotype 3 MM interaction. The random error term used to test MM effects was generated using the pen 3 block 3 MM interaction; whereas, genotype and the genotype 3 MM interaction were tested for significance using the random residual. Least squares means were computed for the main and interactive effects, and were separated statistically using the probability of difference (PDIFF) option. Frequencies of American and Japanese color scores were analyzed by chi-square analysis (Ott, 1988), using the frequency procedure (SAS Institute).
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
3. Results and discussion There were no significant (P , 0.10) genotype 3 MM interactions. Therefore, only main effects are reported within the text.
3.1. Live animal performance The effect of halothane-genotype on ADG is reported in Table 2. Although ADG was similar among NN and Nn pigs during the starter phase, NN pigs had higher ADG during the grower (P , 0.05) and finisher (P , 0.05) phases, as well as over the entire feeding trial (P , 0.05) than Nn pigs. It should be noted that because each experimental unit (pen) contained both NN and Nn pigs, it was impossible to calculate and report ADFI and G:F.
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Results from the present study are in agreement with those of Jensen and Barton-Gade (1985), who reported that NN pigs had greater ADG than Nn pigs. In contrast, however, Luescher et al. (1979) observed that Nn pigs had greater growth rates than NN pigs. Moreover, the majority of the available research has repeatedly shown little to no difference in ADG between homozygous negative and halothane-carriers (Eikelenboom et al., 1980; Leach et al., 1996; Pommier et al., 1992; Sather et al., 1991c; Sather and Jones, 1996). Results from the present study may be somewhat misleading because the dam- and sire-lines used to produce the NN pigs have been extensively selected for rapid growth rates, but it cannot be ignored that the progeny from mating this rapid growth rate dam-line to reactor sires depressed growth rate significantly.
Table 2 Effects of halothane genotype and magnesium mica level on performance of growing-finishing swine Item a
Halothane genotype b NN
Nn
Starter phase (17.4–34.0 kg) ADG (g / d) ADFI (g / d) G:F
0.619 – –
0.604 – –
Grower phase (34.0–68.2 kg) ADG (kg / day) ADFI (kg / day) G:F
0.948 d – –
Finisher phase (68.2–108.8 kg) ADG (kg / day) ADFI (kg / day) G:F
RSE c
RSE c
Magnesium mica (%) 0.00
1.25
2.50
0.121
0.648 1.369 0.474 f
0.602 1.305 0.462 fg
0.584 1.334 0.437 g
0.120 0.190 0.051
0.896 e – –
0.121
0.940 2.331 0.404 fg
0.920 2.222 0.415 f
0.893 2.276 0.393 g
0.120 0.335 0.032
0.899 d – –
0.845 e – –
0.147
0.859 2.724 0.315
0.864 2.721 0.317
0.874 2.745 0.319
0.133 0.285 0.025
Overall (17.4–108.8 kg) ADG (kg / day) ADFI (kg / day) G:F
0.848 d – –
0.804 e – –
0.087
0.834 2.263 0.369
0.819 2.213 0.371
0.812 2.248 0.361
0.076 0.190 0.019
Weights (kg) Initial Starter phase Grower phase Finisher phase
17.64 34.46 69.76 d 111.95 d
17.28 33.64 67.04 e 106.78 e
1.126 3.551 6.062 9.873
17.41 34.91 69.92 f 110.30
17.44 33.74 68.02 fg 108.47
17.43 33.37 66.65 g 107.63
0.063 3.415 4.743 8.728
a
ADG 5 average daily gain; ADFI 5 average daily feed intake; and G:F 5 gain-to-feed ratio. NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. c Residual standard error. d,e Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). f,g Within a row, magnesium mica least squares means lacking a common superscript letter differ (P , 0.05). b
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Supplementing the diets of growing-finishing swine with MM did not (P . 0.10) affect ADG or ADFI during the starter, grower, or finisher phases, as well as over the entire length of the feeding trial (Table 2). Pigs fed the control diet, during the starter phase, had greater (P , 0.05) G:F than pigs fed the diet supplemented with 2.5% MM. During the grower phase, however, pigs fed 1.25% MM were more (P , 0.05) efficient than pigs fed 2.5% MM, with pigs consuming the control diet having G:F intermediate to those of the MM-fed pigs (0.415, 0.393, and 0.404, respectively). Gain-to-feed ratios were similar (P . 0.10) among treatments during the finisher phase or over the duration of the trial. O’Quinn et al. (2000) reported that ADG, ADFI, and G:F were not affected by inclusion of Mg sulfate in the diets of finishing pigs. Similarly, the long-term inclusion of MM in swine diets had no effect on ADG, ADFI, or G:F during the starter, grower, or finisher phases, or during the entire trial (Apple et al., 2000). Moreover, neither Coffey and Brazle (1995) nor Watson et al. (1998) observed any beneficial, or deleterious, effects of dietary MM on growth rate or feed efficiency when fed to beef cattle and sheep. It is interesting to note that the energy density of diets decreased as the level of MM increased from 0 to 2.5% (Table 1). The activation of several enzymes in intermediary metabolism by Mg led Heaton (1973) to speculate that increased cellular Mg concentrations may increase enzyme activity, with the net result being improved energy
utilization / efficiency. Thus, the lack of a reduction in ADG in pigs fed diets supplemented with MM in this and a previous study (Apple et al., 2000), as well as the improved G:F in pigs fed 1.25% MM during the grower phase, may suggest an improvement in overall energy efficiency.
3.2. Carcass yield characteristics Carcasses from Nn pigs had less (P , 0.05) fat opposite the first rib, last rib, and last lumbar vertebra, as well as less (P , 0.05) average backfat, than carcasses from NN pigs (Table 3). Moreover, carcasses of Nn pigs had considerably less (P , 0.05) fat at the tenth rib (22.2 vs. 32.5 mm), and greater (P , 0.05) LM depth (59.8 vs. 50.9 mm) than carcasses from NN pigs. It is evident from published studies that homozygous recessive (nn) pigs produce leaner, heaviermuscled carcasses than heterozygous (Nn) and homozygous dominant (NN) pigs (Eikelenboom et al., 1980; Jones et al., 1988; Murray et al., 1989; Sather et al., 1991a; Zhang et al., 1992); however, definitive differences in carcass composition between heterozygotes (Nn) and homozygous negative (NN) pigs have not been as well established. Eikelenboom et al. (1980) reported that carcasses from Nn pigs had less average backfat than carcasses from NN pigs, and Murray et al. (1989) reported that carcasses from Nn pigs had approximately 14% less fat than carcasses from NN pigs. Other studies,
Table 3 Effects of halothane genotype and magnesium mica level on carcass yield characteristics Item
Backfat measurements (cm) First rib Last rib Last lumbar vertebra Average backfat Tenth rib fat depth (mm) Longissimus muscle depth (mm) Percentage muscle c a
Halothane genotype a NN
Nn
5.6 d 3.8 d 3.8 d 4.4 d 32.5 d 50.9 e 46.6 e
4.5 e 3.2 e 2.8 e 3.5 e 22.2 e 59.8 d 52.1 d
RSE b
0.953 0.693 0.779 0.606 5.716 6.322 2.598
RSE b
Magnesium mica (%) 0.00
1.25
2.50
5.1 3.7 3.3 4.0 27.3 55.9 49.4
5.1 3.6 3.4 4.0 27.5 54.6 49.0
5.0 3.3 3.1 3.8 27.1 55.6 49.48
0.949 0.696 0.759 0.632 5.819 6.261 2.656
NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. Residual standard error. c Percentage muscle 5 ((2.827 1 (0.469 3 carcass wt, lb) 1 9.824 3 [tenth rib fat depth, mm 3 0.0393701]) 2 (18.47 3 [longissimus muscle depth, mm 3 0.0393701]) 4 carcass wt) 3 100. d,e Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). b
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
however, have shown that carcasses from NN and Nn pigs had similar midline backfat measurements and tenth rib fat depths (Leach et al., 1996; Pommier et al., 1992; Sather and Jones, 1996; Sutton et al., 1997). Moreover, Simpson and Webb (1989) and Jones et al. (1988) found that carcasses from Nn pigs were actually fatter than carcasses from NN pigs. As for carcass muscling, results from the present study are comparable to those of Sather and Jones (1996) and Jones et al. (1988), who reported that carcasses from Nn pigs had greater LM depth and a higher percent muscle than carcasses from NN pigs. Furthermore, Sather et al. (1991a) reported that carcasses from Nn pigs had higher weights of total lean, as well as greater carcass muscle, than carcasses from NN pigs. In contrast, several studies have failed to denote differences in LM area or depth and carcass muscle percentage among carcasses from NN and Nn pigs (Leach et al., 1996; Pommier et al., 1992; Sutton et al., 1997). Supplementation of swine diets with MM had no effect (P . 0.10) on midline backfat measurements, tenth rib fat depth, LM depth, or percentage muscle (Table 3). These results are consistent with those of
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Schaefer et al. (1993) and D’Souza et al. (1998, 1999), who failed to note an effect of supplemental Mg on any fat or muscle measurement of pork carcasses; however, these authors fed Mg aspartate for a brief 5-day period before harvest. In the first experiment, Apple et al. (2000) reported no effect of long-term supplementation of MM on pork carcass composition, but, in the second experiment, they reported a 0.19 to 0.44 cm reduction in tenth rib fat depth, and a 0.89 to 1.44% increase in percent muscle of carcasses from pigs fed 2.50 and 1.25% MM, respectively.
3.3. Pork quality characteristics Although LM pH was not affected (P . 0.10) by halothane genotype, drip loss percentages were higher (P , 0.05), and LM moisture content was lower (P , 0.05), in pork from Nn pigs compared to NN pigs (Table 4). The LM from Nn pigs received lower (P , 0.05) marbling, firmness, and color scores than the LM from NN pigs. Moreover, pork from Nn pigs was lighter (P , 0.05), less (P , 0.05) red, and less (P , 0.05) yellow compared to that from NN pigs,
Table 4 Effects of halothane genotype and magnesium mica level on pork quality characteristics Item
Longissimus muscle pH Drip loss (%) Moisture content c (%) American color score d Japanese color score e Marbling score f Firmness score g Lightness h (CIE L*) Redness h (CIE a*) Yellowness h (CIE b*) a
Halothane genotype a NN
Nn
5.70 2.26 j 72.29 i 3.4 i 3.0 i 2.2 i 2.9 i 53.93 j 8.02 i 18.31 i
5.71 3.63 i 71.38 j 2.4 j 2.1 j 1.5 j 2.6 j 59.34 i 7.29 j 17.71 j
RSE b
0.260 2.078 1.559 0.779 0.779 0.779 0.866 4.157 1.386 1.732
RSE b
Magnesium mica (%) 0.00
1.25
2.50
5.73 3.07 71.63 2.8 2.5 1.9 2.7 57.05 7.72 17.95
5.67 2.72 71.91 3.1 2.7 1.9 2.7 55.93 7.75 17.82
5.71 3.05 71.98 2.8 2.5 1.8 2.9 56.91 7.49 17.71
0.253 2.150 1.391 0.822 0.759 0.822 0.949 4.301 1.518 1.961
NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. Residual standard error. c Longissimus muscle moisture content determined by freeze-drying. d American color score: 1 5 pale pinkish gray and 6 5 dark purplish red (NPPC, 1999). e Japanese color score: 1 5 pale gray and 6 5 dark purple (Nakai et al., 1975). f Marbling score: 1 5 1% intramuscular lipid and 10 5 10% intramuscular lipid (NPPC, 1999). g Firmness score: 1 5 very soft / very watery and 5 5 very firm / dry (NPPC, 1991). h L* 5 measure of darkness to lightness (larger number indicates a lighter color); a* 5 measure of redness (larger number indicates a more intense red color); and b* 5 measure of yellowness (larger number indicates more yellow color). i,j Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). b
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and a higher proportion of carcasses from Nn pigs received American and Japanese color scores indicating PSE pork (Table 5). It is generally accepted that the pork quality of pigs homozygous positive (nn) for the halothane gene is considerably inferior to that of homozygous negative (NN) pigs (De Smet et al., 1996; Jones et al., 1988; Murray et al., 1989; Sather et al., 1991a,b,c; Tam et al., 1998; Zhang et al., 1992). However, when comparing pork quality traits of heterozygous carriers (Nn) to either homozygous genotype, results are not as clear. Jeremiah et al. (1999) reported higher color, marbling, and structure scores for pork from NN pigs than Nn pigs. Similarly, Sather and Jones (1996), Leach et al. (1996), and Sather et al. (1991c) found that Nn pigs produced pork with lower pH and greater drip loss than pork from NN pigs, and Simpson and Webb (1989) reported a higher percentage of pork carcasses from Nn pigs were PSE than carcasses from NN pigs. Contrary to those studies, Murray et al. (1989) reported that pork from Nn pigs was redder (higher a* value) than pork from NN pigs, and even though Sutton et al. (1997) reported that the LM from Nn pigs had higher drip loss percentages and received
lower color and firmness scores than NN pigs, they failed to find a difference in CIE L*, a*, and b* values, as well as LM moisture and marbling content, between the two genotypes. Still other studies have shown that the pork quality attributes of Nn pigs were quite similar to those of NN pigs (De Smet et al., 1996; Murray and Johnson, 1998; Pommier et al., 1992; Sather et al., 1991b; Tam et al., 1998). The pH of the LM was not affected (P . 0.10) by inclusion of MM in the diets of growing finishing pigs (Table 4). Even though Apple et al. (2000) failed to denote a difference in the ultimate pH of the LM from long-term supplementation of swine diets with MM, Otten et al. (1992) reported that long-term supplementation of swine diets with Mg fumarate effectively elevated muscle pH. Additionally, several authors have reported that feeding diets fortified with Mg, or giving intravenous injections of Mg, shortly before harvest increased initial and / or ultimate muscle pH (Campion et al., 1971; D’Souza et al., 1998, 1999, 2000; Schaefer et al., 1993). It is not unusual for ultimate muscle pH values to be virtually alike in both PSE and normal muscle, but 45-min pH values are critical to the development of PSE pork. Thus, the lack of a discernable difference in the ultimate
Table 5 Effect of halothane genotype and magnesium mica level on the frequency (%) of American a and Japanese b color scores Halothane genotype c
American color scores 1 2 3 4
NN
Nn
0.00
1.25
2.50
0.00 5.56 18.52 13.88
12.03 25.93 21.30 2.78
3.70 12.04 14.81 2.78
3.70 9.26 9.26 10.19
4.63 10.19 15.74 3.70
0.93 12.04 22.22 2.78
18.52 31.47 12.04 0.00
6.48 15.74 11.11 0.00
7.41 10.18 13.89 0.93
5.56 17.59 9.26 1.85
d,e
Japanese color scores f,g 1 2 3 4 a
Magnesium mica (%)
American color score: 1 5 pale pinkish gray and 6 5 dark purplish red (NPPC, 1999). Japanese color score: 1 5 pale gray and 6 5 dark purple (Nakai et al., 1975). c NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. d Chi-Square statistic for halothane genotype 5 30.981 (P , 0.001). e Chi-square statistic for magnesium mica level 5 8.971 (P , 0.175). f Chi-square statistic for halothane genotype 5 28.22 (P , 0.001). g Chi-square statistic for magnesium mica level 5 5.468 (P , 0.485). b
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
pH of the LM from pigs fed MM is neither surprising nor unexpected. Supplementation of swine diets with MM had no effect (P . 0.10) on drip loss percentages and moisture contents of the LM (Table 4). Results of the present study confirm previously published information from our laboratory that long-term supplementation of swine diets with MM did not affect LM drip loss or moisture content (Apple et al., 2001). Moreover, Otten et al. (1992) failed to denote an effect of long-term supplementation of swine diets with Mg fumarate on the water-holding capacity of pork LM. However, feeding diets supplemented with Mg aspartate or Mg sulfate significantly reduced drip loss percentages, even when fed for only 2 days prior to slaughter (D’Souza et al., 2000). Moreover, inclusion of supplemental Mg for 5 days before harvest significantly lowered drip loss in the LM of pigs heterozygous for the halothane-gene (D’Souza et al., 1998, 1999; Schaefer et al., 1993; Schmitten et al., 1984) and heterozygous for the RN gene (Hemann et al., 2000). Both subjective color scores and objective color measurements of the LM were similar (P . 0.10) among carcasses from pigs fed 0.0, 1.25 and 2.50% MM (Table 4). Moreover, dietary MM had no effect (P . 0.10) on the percentage of carcasses with color scores characteristic of PSE pork (Table 5). Neither O’Quinn et al. (2000) nor D’Souza et al. (1999) found a difference in pork color among pigs fed diets containing supplemental Mg. On the other hand, D’Souza et al. (1998) reported lower L* values, and Schaefer et al. (1993) reported higher a* values, for LM chops from pigs supplemented with Mg aspartate 5 days before slaughter. Similarly, the percentage of PSE, or PSE-like, carcasses was greatly reduced by the short-term (D’Souza et al., 1998, 2000) or long-term (Apple et al., 2000) Mg supplementation.
4. Conclusions Data from the present study supports the tenet that pork from Nn pigs was inferior in quality attributes, having had a higher percentage of carcasses with quality traits characteristic of PSE pork. However, inclusion of MM in the diets of growing-finishing
111
swine had no appreciable effects on pork quality or on the percentage of carcasses deemed PSE. The lack of any discernable effect of MM on pork quality may be due to two pre-eminent factors: (1) the bioavailability of Mg from MM (which is largely unknown in swine), and / or (2) length of supplementation. Even though results of the present study support the notion that short-term, rather than long-term, Mg supplementation is apparently more effective in improving pork quality, the formulation / production, transportation, and distribution of specialized diets containing elevated levels of Mg for only the last 5 to 7 days of the finishing period may not be a practical, and economically feasible, management step, especially in large, integrated production systems. Inclusion of MM, an inexpensive source of Mg, in starter, grower and / or finisher diets may be more easily incorporated into pre-existing management practices. Moreover, the small economic benefits realized from moderate improvements in feed efficiency and lower diet costs (Apple et al., 2000) makes the long-term MM supplementation an attractive management decision for today’s integrated swine industry. Even though MM supplementation had no beneficial, or deleterious, effects on pork quality in this study, results from this study indicate a need for additional research, specifically whether a shorter duration of MM-supplementation (in particular during the finishing period only) would be more effective in improving pork quality compared to the long-term supplementation program utilized in the present study.
Acknowledgements The authors wish to express their appreciation to Micro-Lite Inc., Chanute, KS, for donation of the magnesium mica and partial financial support of this project. Additionally, the authors fully acknowledge the assistance of Ben Wheeler and the Research and Development staff of Seaboard Farms Inc. in carcass data collection and loin procurement. Finally, the authors wish to thank Ashley Hays, Lance Kirkpatrick, Dari Brown, Ellen Davis, and Joe Leibbrandt for animal care, and Jerry Stephenson, Jennifer Leach, Rebecca Miller, Nicholas Simon, and Joel
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Reiman for assistance in loin fabrication and pork quality data collection.
References Apple, J.K., Davis, J.R., Rakes, L.K., Maxwell, C.V., Stivarius, M.R., Pohlman, F.W., 2001. Effects of dietary magnesium and duration of refrigerated storage on the quality of vacuumpackaged, boneless pork loins. Meat Sci. 57, 43–53. Apple, J.K., Maxwell, C.V., de Rodas, B., Watson, H.B., Johnson, Z.B., 2000. Effect of magnesium mica on performance and carcass quality of growing-finishing swine. J. Anim. Sci. 78, 2135–2143. Campion, D.R., Marsh, B.B., Schmidt, G.R., Cassens, R.G., Kauffman, R.G., Briskey, E.J., 1971. Use of whole-body perfusion in the study of muscle glycolysis. J. Food Sci. 36, 545–548. Coffey, K.P., Brazle, F.K., 1995. Performance of finishing steers offered magnesium-mica in the feedlot ration. Kansas State University Southeast Agric. Res. Rep. 733, 15–19. De Smet, S.M., Pauwels, H., De Bie, S., Demeyer, D.I., Callewier, J., Eeckhout, W., 1996. Effect of halothane genotype, breed, feed withdrawal, and lairage on pork quality of Belgian slaughter pigs. J. Anim. Sci. 74, 1854–1863. D’Souza, D.N., Warner, R.D., Dunshea, F.R., Leury, B.J., 1999. Comparison of different dietary magnesium supplements on pork quality. Meat Sci. 51, 221–225. D’Souza, D.N., Warner, R.D., Leury, B.J., Dunshea, F.R., 1998. The effect of dietary magnesium aspartate supplementation on pork quality. J. Anim. Sci. 76, 104–109. D’Souza, D.N., Warner, R.D., Leury, B.J., Dunshea, F.R., 2000. The influence of dietary magnesium supplement type, and supplementation dose and duration, on pork quality and the incidence of PSE pork. Aust. J. Agric. Res. 51, 185–189. Eikelenboom, G., Minkema, D., Van Eldik, P., Sybesma, W., 1980. Performance of Dutch Landrace pigs with different genotypes for the halothane-induced malignant hyperthermia syndrome. Livest. Prod. Sci. 7, 317–324. Heaton, F.W., 1973. Magnesium requirement for enzymes and hormones. Biochem. Soc. Trans. 1, 67–70. Hemann, M.D., Ellis, M., McKeith, F.K., Miller, K.D., Purser, K., 2000. The effect of rendement napole genotype and time of feeding of supplemental magnesium sulfate on carcass characteristics and on pork quality. J. Anim. Sci. 78 (Suppl. 2), 49. Jensen, P., Barton-Gade, P.A, 1985. Performance and carcass characteristics of pigs with known genotypes for halothane susceptibility. In: EAAP Publ. No. 33. Pudoc, Wageningen, The Netherlands, pp. 80–87. Jeremiah, L.E., Gibson, J.P., Gibson, L.L., Ball, R.O., Aker, C., Fortin, A., 1999. The influence of breed, gender, and PSS (halothane) genotype on meat quality, cooking loss, and palatability of pork. Food Res. Int. 32, 59–71. Jones, S.D.M., Murray, A.C., Sather, A.P., Robertson, W.M., 1988. Body proportions and carcass composition of pigs with known genotypes for stress susceptibility fasted for different periods of time prior to slaughter. Can. J. Anim. Sci. 68, 139–149.
Kuhn, G., Nowak, A., Otto, E., Albrecht, V., Gassman, B., Sandner, E., Przybilski, H., Zahn, L., 1981. Studies on the control of meat quality by special treatment of swine. 1. Effects of stress and preventative magnesium feeding on selected parameters of carcass value and blood serum. Arch. Tierz. 24, 217–225. Leach, L.M., Ellis, M., Sutton, D.S., McKeith, F.K., Wilson, E.R., 1996. The growth performance, carcass characteristics, and meat quality of halothane carrier and negative pigs. J. Anim. Sci. 74, 934–943. Littledike, E.T., Stuedemann, J.A., Wilkinson, S.R., Horst, R.L., 1983. Grass tetany syndrome. In: Fontenot, J.P., Bunce, G.E., Weeb, Jr. K.E., Allen, V.G. (Eds.), Role of Magnesium in Animal Nutrition. Virginia Polytechnic Inst. and St. Univ, Blacksburg, VA, pp. 173–197. Luescher, U., Schnieder, A., Jucker, H., 1979. Genetics of halothane-sensitivity and change of performance, carcass and meat quality traits induced by selection against halothanesensitivity. In: Proceedings of the 30th Annual Meeting of the EAAP, Harrogate, UK, paper MP 2.11. Murray, A.C., Johnson, C.P., 1998. Impact of the halothane gene on muscle quality and pre-slaughter deaths in Western Canadian pigs. Can. J. Anim. Sci. 78, 543–548. Murray, A.C., Jones, S.D.M., Sather, A.P., 1989. The effect of preslaughter feed restriction and genotype for stress susceptibility on pork lean quality and composition. Can. J. Anim. Sci. 69, 83–91. Nakai, H., Saito, F., Ikeda, T., Anso, S., Komatsu, A., 1975. Standard models of pork colour. Bull. Natl. Inst. Anim. Industry (Chiba) 29, 69–75. NPPC, 1991. Procedures to Evaluate Market Hogs, 3rd Edition. National Pork Producers Council, Des Moines, IA. NPPC, 1999. Official Color and Marbling Standards. National Pork Producers Council, Des Moines, IA. NRC, 1998. Nutrient Requirements of Swine, 10th Edition. National Academy Press, Washington, DC. O’Quinn, P.R., Nelssen, J.L., Unruh, J.A., Goodband, R.D., Woodworth, J.C., Tokach, M.D., 2000. Effects of feeding modified tall oil and supplemental potassium and magnesium on growth performance, carcass characteristics, and meat quality of growing-finishing pigs. Can. J. Anim. Sci. 80, 443–449. Ott, L., 1988. An Introduction to Statistical Methods and Data Analysis, 3rd Edition. PWS-Kent Publishing Co, Boston, MA. Otten, W., Berrer, A., Hartmann, S., Bergerhoff, T., Eichinger, H.M., 1992. Effects of magnesium fumarate supplementation on meat quality in pigs. In: Proceedings of the 38th International Congress on Meat Science Technology, Clermont-Ferrand, France, pp. 117–120. Pommier, S.A., Houde, A., Rousseau, F., Savoie, Y., 1992. The effect of the malignant hyperthermia genotype as determined by a restriction endonuclease assay on carcass characteristics of commercial crossbred pigs. Can. J. Anim. Sci. 72, 973–976. Sather, A.P., Jones, S.D.M., 1996. The effect of genotype on feedlot performance, carcass composition, and lean meat quality from commercial pigs. Can. J. Anim. Sci. 76, 507–516. Sather, A.P., Jones, S.D.M., Tong, A.K.W., 1991a. Halothane
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113 genotype by weight interactions on lean yield from pork carcasses. Can. J. Anim. Sci. 71, 633–643. Sather, A.P., Jones, S.D.M., Tong, A.K.W., Murray, A.C., 1991b. Halothane genotype by weight interactions on pig meat quality. Can. J. Anim. Sci. 71, 645–658. Sather, A.P., Murray, A.C., Zawadski, S.M., Johnson, P., 1991c. The effect of the halothane gene on pork production and meat quality of pigs reared under commercial conditions. Can. J. Anim. Sci. 71, 959–967. Schaefer, A.L., Murray, A.C., Tong, A.K.W., Jones, S.D.M., Sather, A.P., 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. ¨ Schmitten, F., Jungst, H., Schepers, K.H., Festerling, A., 1984. ¨ Untersuchungen uber die Wirkung des magnesiumhaltigen ¨ Ergazungsfuttermittels ‘Cytran ’ auf die Fleischbeschaffenheit ¨ von streßanfalligen Schweinen. Dtsch. Tierz. Wochenschr. 91, 149–151. Simpson, S.P., Webb, A.J., 1989. Growth and carcass performance
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of British Landrace pigs heterozygous at the halothane locus. Anim. Prod. 49, 503–509. Sutton, D.S., Ellis, M., Lan, Y., McKeith, F.K., Wilson, E.R., 1997. Influence of slaughter weight and stress gene genotype on the water-holding capacity and protein gel characteristics of three porcine muscles. Meat Sci. 46, 173–180. Tam, L.G., Berg, E.P., Gerrard, D.E., Sheiss, E.B., Tan, F.J., Okos, M.R., Forrest, J.C., 1998. Effect of halothane genotype on porcine meat quality and myoglobin autoxidation. Meat Sci. 49, 41–53. USDA, 1995. Institutional Meat Purchase Specifications for Fresh Pork Products. Agricultural Marketing Service, USDA, Washington, DC. Watson, H.B., Coffey, K.P., Kegley, E.B., Apple, J.K., Ratchford, W.R., 1998. Comparison of magnesium sources in diets of finishing lambs. J. Anim. Sci. 76 (Suppl. 1), 359. Zhang, W., Kuhlers, D.L., Rempel, W.E., 1992. Halothane gene and swine performance. J. Anim. Sci. 70, 1307–1313.
Effects of dietary magnesium and halothane genotype on performance and carcass traits of growing-finishing swine Jason K. Apple*, Charles V. Maxwell, Matthew R. Stivarius, Lilly K. Rakes, Zelpha B. Johnson Department of Animal Science, B103 C AFLS Administration Building, University of Arkansas, Fayetteville, AR 72701, USA Received 25 April 2001; received in revised form 31 December 2001; accepted 31 December 2001
Abstract Halothane-negative (NN) and halothane-carrier (Nn) pigs were assigned randomly to one of three dietary treatments: (1) control corn–soybean meal diets; (2) control diets supplemented with 1.25% magnesium mica (MM); or (3) control diets supplemented with 2.5% MM. When the lightest block averaged 108.8 kg, pigs were harvested at a commercial pork slaughter plant, and bone-in pork loins were captured, vacuum-packaged and transported back for measurement of pork quality traits. The NN pigs had greater average daily gain (ADG) during the grower (P , 0.05) and finisher (P , 0.05) periods than Nn pigs. Although MM had no effect (P . 0.10) on ADG, pigs fed 1.25% MM had a higher (P , 0.05) gain-to-feed ratio (G:F) during the grower phase than pigs fed 2.5% MM; whereas, pigs fed control diets had an intermediate G:F. Carcasses from Nn pigs were leaner (P , 0.05) and heavier (P , 0.05) muscled than carcasses from NN pigs. In contrast, a greater (P , 0.05) percentage of carcasses from Nn pigs received color scores characteristic of the pale, soft and exudative (PSE) condition. Although there were distinct genotype effects on performance and carcass traits, long-term supplementation of diets with MM had no beneficial, or deleterious, effects on pork quality or carcass yield. 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnesium; Genotype; Pig-feeding and nutrition; Carcass composition; Pork quality
1. Introduction The incorporation of supplemental magnesium (Mg) into animal diets has traditionally been used to prevent the metabolic disorders associated with Mg deficiency (Littledike et al., 1983). However, research has shown that supplementing swine diets with Mg reduced the stress responses in pigs *Corresponding author. Tel.: 1 1-479-575-4840; fax: 1 1-479575-7294. E-mail address: [email protected] (J.K. Apple).
(D’Souza et al., 1998), producing visibly calmer pigs after long-distance transportation (Kuhn et al., 1981). Moreover, dietary inclusion of Mg has been reported to have beneficial effects on pork quality traits (D’Souza et al., 1998, 1999, 2000; Hemann et al., 2000; Otten et al., 1992), and reducing the incidence of pale, soft and exudative (PSE) pork (D’Souza et al., 1998; Schaefer et al., 1993). The magnitude of responses to supplemental Mg on pork quality traits appears to be related to the stress-susceptibility, or resistance, of the pigs being studied. Campion et al. (1971) reported that muscle
0301-6226 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 02 )00004-0
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J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
pH was higher in stress-susceptible pigs intravenously infused with Mg chloride prior to harvest, but muscle pH was not affected by Mg-infusion in stress-resistant pigs. Likewise, Schmitten et al. (1984) reported that supplementing swine diets for 5 days before harvest with Mg aspartate resulted in improvements in pork color and moisture retention in halothane-positive pigs, but not in halothane-negative pigs. Moreover, the improvements in pork quality in response to short-term supplementation of Mg aspartate reported by Schaefer et al. (1993) were for only confirmed heterozygous carriers of the halothane gene. Muscle drip loss percentages were also reduced when pigs, heterozygous for the rendement napole (RN) gene, were fed diets containing Mg sulfate for 3 to 5 days prior to harvest, but no appreciable effect of dietary Mg was noted in pigs homozygous negative for this gene (Hemann et al., 2000). Magnesium mica (MM) is an inorganic, layered silicate product, containing approximately 8% Mg, that has been used primarily as a pellet binder in the feed milling industry. When incorporated in high concentrate diets of beef cattle, dietary MM was found to increase longissimus thoracis marbling scores and beef quality grades (Coffey and Brazle, 1995). In the first of two experiments from our laboratory (Apple et al., 2000), long-term supplementation of swine diets with MM improved pork color and reduced the proportion of carcasses with quality traits characteristic of PSE pork; however, in the second experiment, dietary MM had no appreciable effects on any pork quality trait measured. Diets for both experiments were identical, but pig populations had changed from a herd of unknown halothane-genotype to an almost exclusively halothane-negative herd in the year between experiments. Therefore, the aim of this experiment was to test the effects of feeding MM during the growingfinishing period on the performance and pork quality traits of halothane-carrier and homozygous-negative pigs.
2. Materials and methods
2.1. Animals and diets Prior to breeding, hair samples from a population
(n 5 30) of Yorkshire 3 Landrace females were collected, packaged, and shipped to Pig Improvement Company headquarters in Franklin, KY, where hairsamples were analyzed for halothane-genotype by their laboratory. All females that were homozygous dominant (NN), or negative, for the halothane-gene were selected and mated to either Duroc 3 Hampshire males (Line TT, The Pork Group, Rogers, AR), tested and guaranteed to be homozygous dominant for the halothane-gene, or to synthetic-bred males (Pig Improvement Company), tested and guaranteed to be homozygous recessive (nn) for the halothane-gene. Pigs generated from these matings were either homozygous dominant / negative (NN) or heterozygous (Nn) carriers of the halothane-gene. Halothane-negative (n 5 45) and halothane-carrier (n 5 75) barrows and gilts, with an average initial body weight (BW) of 17.463.2 kg, were moved from the University of Arkansas Nursery to the University of Arkansas Swine Growing-Finishing Facility and blocked by BW into four blocks. Pigs were then allotted randomly to pens (six pens / block) based on sex and litter origin / genotype, with at least one NN pig / pen (15, 13, 11, and six NN-pigs in blocks 1, 2, 3, and 4, respectively), and one of three treatments was assigned randomly to pens (five pigs / pen) within blocks. Pigs were fed ad libitum a three-phase diet with transition from starter to grower when the average block BW was 34.0 kg, and from the grower to finisher when the mean block BW was 68.2 kg. A total of 24 pens were assigned randomly to one of three treatments: (1) a negative control corn–soybean meal starter, grower, and finisher diets devoid of supplemental magnesium; (2) the control starter, grower, and finisher diets supplemented with 1.25% MM (Micro-Lite Inc., Chanute, KS); or (3) the control starter, grower, and finisher diets supplemented with 2.5% MM (Table 1). Within the MM-supplemented diets, MM was added at the expense of corn. All diets were formulated to meet, or exceed, NRC (1998) requirements for growingfinishing swine, and starter, grower, and finisher diets contained 1.10, 0.95, and 0.85% lysine, respectively (Table 1). Individual pig weights were measured weekly, and feed disappearance was recorded during each phase to calculate average daily gain (ADG), average daily feed intake (ADFI), and gainto-feed ratio (G:F).
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Table 1 Composition of experimental diets Ingredient (% dry matter)
Starter diets
Grower diets
Finisher diets
0.00
1.25
2.50
0.00
1.25
2.50
0.00
1.25
2.50
61.78 30.75 4.00 1.55 0.00 0.82 0.50 0.15 0.25 0.13 0.05 0.03
60.28 31.00 4.00 1.55 1.25 0.82 0.50 0.15 0.25 0.13 0.05 0.03
59.10 30.90 4.00 1.60 2.50 0.82 0.50 0.15 0.25 0.13 0.05 0.03
66.98 25.60 4.00 1.65 0.00 0.77 0.50 0.15 0.15 0.13 0.05 0.03
65.73 25.60 4.00 1.65 1.25 0.77 0.50 0.15 0.15 0.13 0.05 0.03
64.30 25.75 4.00 1.70 2.50 0.77 0.50 0.15 0.15 0.13 0.05 0.03
71.12 21.90 4.00 1.45 0.00 0.68 0.50 0.10 0.13 0.05 0.05 0.03
69.87 21.90 4.00 1.45 1.25 0.68 0.50 0.10 0.13 0.05 0.05 0.03
68.62 21.90 4.00 1.50 2.50 0.68 0.50 0.10 0.13 0.05 0.05 0.03
Calculated composition (% dry matter) Crude protein (CP) 20.17 Lysine 1.10 Methionine 0.32 Methionine and cysteine 0.67 Threonine 0.78 Tryptophan 0.24 Magnesium 0.18 Calcium 0.80 Phosphorus 0.65 Metabolizable energy (Mcal / kg) 3.45
20.16 1.10 0.32 0.67 0.78 0.24 0.28 0.80 0.65 3.40
20.01 1.10 0.32 0.67 0.78 0.24 0.38 0.80 0.65 3.36
18.11 0.95 0.29 0.61 0.70 0.21 0.18 0.80 0.65 3.45
18.00 0.95 0.29 0.61 0.70 0.21 0.28 0.80 0.65 3.41
17.95 0.95 0.29 0.61 0.70 0.21 0.38 0.80 0.65 3.36
16.67 0.85 0.27 0.57 0.64 0.19 0.18 0.60 0.60 3.47
16.56 0.85 0.27 0.57 0.64 0.19 0.28 0.60 0.60 3.42
16.45 0.85 0.27 0.57 0.64 0.19 0.38 0.60 0.60 3.38
Corn Soybean meal (48% CP) Animal and vegetable fat Dicalcium phosphate Magnesium mica Calcium carbonate Salt Mineral premix a Vitamin / trace mineral premix b Tylosin-40 Copper sulfate Ethoxyquin
a
Premix consisted of 11.0% Fe, 11.0% Zn, 2.6% Mn, 1.1% Cu, 0.02% I, and 0.02% Se (Nutra Blend Corp., Neosho, MO). Premix consisted of 909,091 IU vitamin A, 136,134 IU vitamin D, 3636 IU vitamin E, 3.6 mg vitamin B12, 364 mg vitamin K, 818 mg riboflavin, 2727 mg D-pantothenic acid, and 4546 mg niacin per kg (Nutra Blend Corp., Neosho, MO). b
2.2. Carcass data collection When the lightest block of pigs averaged 108.8 kg, all pigs were transported approximately 10 h (724 km) to a commercial pork harvest / fabrication plant (Seaboard Farms Inc., Guymon, OK). After a brief 45-min rest period, pigs were harvested according to industry-accepted procedures, and carcasses were chilled rapidly for 1 to 2 h at 2 26 8C, followed by a ‘tempering’ period where temperature was gradually increased from 2 3 to 2 8C. Approximately 24 h post-harvest, fat and longissimus thoracis et lumborum (LM) depths 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 of approximately 7 cm from the midline. Additionally, trained personnel recorded midline backfat measurements opposite the first rib, last rib, and last lumbar vertebra. Carcasses were then fabricated into subpri-
mal cuts according to Institutional Meat Purchasing Specifications (IMPS) for Fresh Pork Products (USDA, 1995). Bone-in pork loins (IMPS [410) were vacuum-packaged in 40 cm 3 100 cm multiply, bone-guard vacuum bags (oxygen transmission rate 5 15 ml / m 2 / 24 h at 23 8C and 1 atm; water transmission rate 5 0.4 g / 645.2 cm 2 / 24 h at 38 8C and 100% relative humidity; Cyrovac Sealed Air Corp., Duncan, SC), boxed, loaded into a refrigerated truck and shipped back to the University of Arkansas Red Meat Abattoir for pork quality measurements.
2.3. Loin fabrication Upon arrival at the abattoir (approximately 48 h after harvest), loins were removed from the vacuumbags, and the pork tenderloin was removed. Then, 7.6 cm of the cranial (blade) portion was removed perpendicular to the length of the loin and discarded.
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Beginning at the cranial end of the loin, two 2.5-cmthick LM chops were cut for color evaluations and two 3.2-cm-thick LM chops were removed for drip loss determinations.
2.4. Pork quality data collection After a 30-min ‘bloom’ period at 4 8C, the 2.5-cmthick LM chops were visually evaluated for marbling (1 5 devoid [1% intramuscular lipid] to 10 5 abundant [10% intramuscular lipid]; NPPC, 1999), firmness (1 5 very soft and watery to 5 5 very firm and dry; NPPC, 1991), and color based on both the American (1 5 pale, pinkish gray to 6 5 dark purplish red; NPPC, 1999) and Japanese color standards (Nakai et al., 1975). The Japanese color standards system is composed of six plastic disks with meatlike texture and appearance developed from objective colorimetry, and scores range from 1 (pale gray) to 6 (dark purple). Commission International de l’Eclairage L*, a*, and b* values were determined from a mean of four random readings (two readings from each of the 2.5-cm-thick LM chops) made with the Hunter MiniScan XE (model 45 / 0-L, Hunter Associates Laboratory, Reston, VA) using illuminant C and a 108 standard observer. The spectrocolorimeter had a 22mm aperture and was calibrated against a standard white tile (No. M04207 with X 5 81.1, Y 5 85.9, and Z 5 91.6; Hunter Associates Laboratory Inc., Reston, VA).
2.5. Drip loss determinations Drip loss, a measure of the water-holding capacity of the LM, was determined according to the suspension procedure described by Apple et al. (2000). Briefly, a 3.2-cm-diameter core was manually removed from each of the 3.2-cm-thick LM chops. Each core was blotted dry on paper towels, core weight was recorded, and the core was suspended on a fish-hook mounted to the lid of a plastic container (46 3 66 3 38 cm deep Dur-X姠 Food Box; Rubbermaid Commercial Products LLC, Winchester, VA). Containers were sealed tightly and stored at 2 8C for 48 h. After the 48-h storage period, each core was removed from its hook, blotted dry with paper
towels, and re-weighed. The loss in weight was divided by the original core, then multiplied by 100 to calculate drip loss percentage.
2.6. Muscle pH and moisture determinations After core removal for drip loss measurements, 2 g of LM were removed, and, subsequently, homogenized in 20 ml of distilled, deionized water. 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., Arvada, CO). Additionally, duplicate samples (approximately 5 g) of LM were weighed, placed in 30-ml beakers, and weighed. Beakers were then placed into vacuum flasks and attached to the manifold of a Labconco freeze-dryer (model 4.5, Labconco Corp., Kansas City, MO) with a temperature setting of 2 50 8C at a vacuum of less than 10 mm of Hg. Samples were freeze-dried for 36 h, and beakers were re-weighed. The difference between the initial and dried beaker weights was divided by the sample weight to calculate the percentage of moisture.
2.7. Statistical analysis All data were analyzed as a split plot design with pen as the experimental unit for performance data and pig as the experimental unit for all carcass data. Analysis of variance was generated using the PROC MIXED procedure (SAS Institute Inc., Cary, NC), with the main effects of genotype and dietary MM, as well as the genotype 3 MM interaction. The random error term used to test MM effects was generated using the pen 3 block 3 MM interaction; whereas, genotype and the genotype 3 MM interaction were tested for significance using the random residual. Least squares means were computed for the main and interactive effects, and were separated statistically using the probability of difference (PDIFF) option. Frequencies of American and Japanese color scores were analyzed by chi-square analysis (Ott, 1988), using the frequency procedure (SAS Institute).
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
3. Results and discussion There were no significant (P , 0.10) genotype 3 MM interactions. Therefore, only main effects are reported within the text.
3.1. Live animal performance The effect of halothane-genotype on ADG is reported in Table 2. Although ADG was similar among NN and Nn pigs during the starter phase, NN pigs had higher ADG during the grower (P , 0.05) and finisher (P , 0.05) phases, as well as over the entire feeding trial (P , 0.05) than Nn pigs. It should be noted that because each experimental unit (pen) contained both NN and Nn pigs, it was impossible to calculate and report ADFI and G:F.
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Results from the present study are in agreement with those of Jensen and Barton-Gade (1985), who reported that NN pigs had greater ADG than Nn pigs. In contrast, however, Luescher et al. (1979) observed that Nn pigs had greater growth rates than NN pigs. Moreover, the majority of the available research has repeatedly shown little to no difference in ADG between homozygous negative and halothane-carriers (Eikelenboom et al., 1980; Leach et al., 1996; Pommier et al., 1992; Sather et al., 1991c; Sather and Jones, 1996). Results from the present study may be somewhat misleading because the dam- and sire-lines used to produce the NN pigs have been extensively selected for rapid growth rates, but it cannot be ignored that the progeny from mating this rapid growth rate dam-line to reactor sires depressed growth rate significantly.
Table 2 Effects of halothane genotype and magnesium mica level on performance of growing-finishing swine Item a
Halothane genotype b NN
Nn
Starter phase (17.4–34.0 kg) ADG (g / d) ADFI (g / d) G:F
0.619 – –
0.604 – –
Grower phase (34.0–68.2 kg) ADG (kg / day) ADFI (kg / day) G:F
0.948 d – –
Finisher phase (68.2–108.8 kg) ADG (kg / day) ADFI (kg / day) G:F
RSE c
RSE c
Magnesium mica (%) 0.00
1.25
2.50
0.121
0.648 1.369 0.474 f
0.602 1.305 0.462 fg
0.584 1.334 0.437 g
0.120 0.190 0.051
0.896 e – –
0.121
0.940 2.331 0.404 fg
0.920 2.222 0.415 f
0.893 2.276 0.393 g
0.120 0.335 0.032
0.899 d – –
0.845 e – –
0.147
0.859 2.724 0.315
0.864 2.721 0.317
0.874 2.745 0.319
0.133 0.285 0.025
Overall (17.4–108.8 kg) ADG (kg / day) ADFI (kg / day) G:F
0.848 d – –
0.804 e – –
0.087
0.834 2.263 0.369
0.819 2.213 0.371
0.812 2.248 0.361
0.076 0.190 0.019
Weights (kg) Initial Starter phase Grower phase Finisher phase
17.64 34.46 69.76 d 111.95 d
17.28 33.64 67.04 e 106.78 e
1.126 3.551 6.062 9.873
17.41 34.91 69.92 f 110.30
17.44 33.74 68.02 fg 108.47
17.43 33.37 66.65 g 107.63
0.063 3.415 4.743 8.728
a
ADG 5 average daily gain; ADFI 5 average daily feed intake; and G:F 5 gain-to-feed ratio. NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. c Residual standard error. d,e Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). f,g Within a row, magnesium mica least squares means lacking a common superscript letter differ (P , 0.05). b
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Supplementing the diets of growing-finishing swine with MM did not (P . 0.10) affect ADG or ADFI during the starter, grower, or finisher phases, as well as over the entire length of the feeding trial (Table 2). Pigs fed the control diet, during the starter phase, had greater (P , 0.05) G:F than pigs fed the diet supplemented with 2.5% MM. During the grower phase, however, pigs fed 1.25% MM were more (P , 0.05) efficient than pigs fed 2.5% MM, with pigs consuming the control diet having G:F intermediate to those of the MM-fed pigs (0.415, 0.393, and 0.404, respectively). Gain-to-feed ratios were similar (P . 0.10) among treatments during the finisher phase or over the duration of the trial. O’Quinn et al. (2000) reported that ADG, ADFI, and G:F were not affected by inclusion of Mg sulfate in the diets of finishing pigs. Similarly, the long-term inclusion of MM in swine diets had no effect on ADG, ADFI, or G:F during the starter, grower, or finisher phases, or during the entire trial (Apple et al., 2000). Moreover, neither Coffey and Brazle (1995) nor Watson et al. (1998) observed any beneficial, or deleterious, effects of dietary MM on growth rate or feed efficiency when fed to beef cattle and sheep. It is interesting to note that the energy density of diets decreased as the level of MM increased from 0 to 2.5% (Table 1). The activation of several enzymes in intermediary metabolism by Mg led Heaton (1973) to speculate that increased cellular Mg concentrations may increase enzyme activity, with the net result being improved energy
utilization / efficiency. Thus, the lack of a reduction in ADG in pigs fed diets supplemented with MM in this and a previous study (Apple et al., 2000), as well as the improved G:F in pigs fed 1.25% MM during the grower phase, may suggest an improvement in overall energy efficiency.
3.2. Carcass yield characteristics Carcasses from Nn pigs had less (P , 0.05) fat opposite the first rib, last rib, and last lumbar vertebra, as well as less (P , 0.05) average backfat, than carcasses from NN pigs (Table 3). Moreover, carcasses of Nn pigs had considerably less (P , 0.05) fat at the tenth rib (22.2 vs. 32.5 mm), and greater (P , 0.05) LM depth (59.8 vs. 50.9 mm) than carcasses from NN pigs. It is evident from published studies that homozygous recessive (nn) pigs produce leaner, heaviermuscled carcasses than heterozygous (Nn) and homozygous dominant (NN) pigs (Eikelenboom et al., 1980; Jones et al., 1988; Murray et al., 1989; Sather et al., 1991a; Zhang et al., 1992); however, definitive differences in carcass composition between heterozygotes (Nn) and homozygous negative (NN) pigs have not been as well established. Eikelenboom et al. (1980) reported that carcasses from Nn pigs had less average backfat than carcasses from NN pigs, and Murray et al. (1989) reported that carcasses from Nn pigs had approximately 14% less fat than carcasses from NN pigs. Other studies,
Table 3 Effects of halothane genotype and magnesium mica level on carcass yield characteristics Item
Backfat measurements (cm) First rib Last rib Last lumbar vertebra Average backfat Tenth rib fat depth (mm) Longissimus muscle depth (mm) Percentage muscle c a
Halothane genotype a NN
Nn
5.6 d 3.8 d 3.8 d 4.4 d 32.5 d 50.9 e 46.6 e
4.5 e 3.2 e 2.8 e 3.5 e 22.2 e 59.8 d 52.1 d
RSE b
0.953 0.693 0.779 0.606 5.716 6.322 2.598
RSE b
Magnesium mica (%) 0.00
1.25
2.50
5.1 3.7 3.3 4.0 27.3 55.9 49.4
5.1 3.6 3.4 4.0 27.5 54.6 49.0
5.0 3.3 3.1 3.8 27.1 55.6 49.48
0.949 0.696 0.759 0.632 5.819 6.261 2.656
NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. Residual standard error. c Percentage muscle 5 ((2.827 1 (0.469 3 carcass wt, lb) 1 9.824 3 [tenth rib fat depth, mm 3 0.0393701]) 2 (18.47 3 [longissimus muscle depth, mm 3 0.0393701]) 4 carcass wt) 3 100. d,e Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). b
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
however, have shown that carcasses from NN and Nn pigs had similar midline backfat measurements and tenth rib fat depths (Leach et al., 1996; Pommier et al., 1992; Sather and Jones, 1996; Sutton et al., 1997). Moreover, Simpson and Webb (1989) and Jones et al. (1988) found that carcasses from Nn pigs were actually fatter than carcasses from NN pigs. As for carcass muscling, results from the present study are comparable to those of Sather and Jones (1996) and Jones et al. (1988), who reported that carcasses from Nn pigs had greater LM depth and a higher percent muscle than carcasses from NN pigs. Furthermore, Sather et al. (1991a) reported that carcasses from Nn pigs had higher weights of total lean, as well as greater carcass muscle, than carcasses from NN pigs. In contrast, several studies have failed to denote differences in LM area or depth and carcass muscle percentage among carcasses from NN and Nn pigs (Leach et al., 1996; Pommier et al., 1992; Sutton et al., 1997). Supplementation of swine diets with MM had no effect (P . 0.10) on midline backfat measurements, tenth rib fat depth, LM depth, or percentage muscle (Table 3). These results are consistent with those of
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Schaefer et al. (1993) and D’Souza et al. (1998, 1999), who failed to note an effect of supplemental Mg on any fat or muscle measurement of pork carcasses; however, these authors fed Mg aspartate for a brief 5-day period before harvest. In the first experiment, Apple et al. (2000) reported no effect of long-term supplementation of MM on pork carcass composition, but, in the second experiment, they reported a 0.19 to 0.44 cm reduction in tenth rib fat depth, and a 0.89 to 1.44% increase in percent muscle of carcasses from pigs fed 2.50 and 1.25% MM, respectively.
3.3. Pork quality characteristics Although LM pH was not affected (P . 0.10) by halothane genotype, drip loss percentages were higher (P , 0.05), and LM moisture content was lower (P , 0.05), in pork from Nn pigs compared to NN pigs (Table 4). The LM from Nn pigs received lower (P , 0.05) marbling, firmness, and color scores than the LM from NN pigs. Moreover, pork from Nn pigs was lighter (P , 0.05), less (P , 0.05) red, and less (P , 0.05) yellow compared to that from NN pigs,
Table 4 Effects of halothane genotype and magnesium mica level on pork quality characteristics Item
Longissimus muscle pH Drip loss (%) Moisture content c (%) American color score d Japanese color score e Marbling score f Firmness score g Lightness h (CIE L*) Redness h (CIE a*) Yellowness h (CIE b*) a
Halothane genotype a NN
Nn
5.70 2.26 j 72.29 i 3.4 i 3.0 i 2.2 i 2.9 i 53.93 j 8.02 i 18.31 i
5.71 3.63 i 71.38 j 2.4 j 2.1 j 1.5 j 2.6 j 59.34 i 7.29 j 17.71 j
RSE b
0.260 2.078 1.559 0.779 0.779 0.779 0.866 4.157 1.386 1.732
RSE b
Magnesium mica (%) 0.00
1.25
2.50
5.73 3.07 71.63 2.8 2.5 1.9 2.7 57.05 7.72 17.95
5.67 2.72 71.91 3.1 2.7 1.9 2.7 55.93 7.75 17.82
5.71 3.05 71.98 2.8 2.5 1.8 2.9 56.91 7.49 17.71
0.253 2.150 1.391 0.822 0.759 0.822 0.949 4.301 1.518 1.961
NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. Residual standard error. c Longissimus muscle moisture content determined by freeze-drying. d American color score: 1 5 pale pinkish gray and 6 5 dark purplish red (NPPC, 1999). e Japanese color score: 1 5 pale gray and 6 5 dark purple (Nakai et al., 1975). f Marbling score: 1 5 1% intramuscular lipid and 10 5 10% intramuscular lipid (NPPC, 1999). g Firmness score: 1 5 very soft / very watery and 5 5 very firm / dry (NPPC, 1991). h L* 5 measure of darkness to lightness (larger number indicates a lighter color); a* 5 measure of redness (larger number indicates a more intense red color); and b* 5 measure of yellowness (larger number indicates more yellow color). i,j Within a row, halothane genotype least squares means lacking a common superscript letter differ (P , 0.05). b
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
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and a higher proportion of carcasses from Nn pigs received American and Japanese color scores indicating PSE pork (Table 5). It is generally accepted that the pork quality of pigs homozygous positive (nn) for the halothane gene is considerably inferior to that of homozygous negative (NN) pigs (De Smet et al., 1996; Jones et al., 1988; Murray et al., 1989; Sather et al., 1991a,b,c; Tam et al., 1998; Zhang et al., 1992). However, when comparing pork quality traits of heterozygous carriers (Nn) to either homozygous genotype, results are not as clear. Jeremiah et al. (1999) reported higher color, marbling, and structure scores for pork from NN pigs than Nn pigs. Similarly, Sather and Jones (1996), Leach et al. (1996), and Sather et al. (1991c) found that Nn pigs produced pork with lower pH and greater drip loss than pork from NN pigs, and Simpson and Webb (1989) reported a higher percentage of pork carcasses from Nn pigs were PSE than carcasses from NN pigs. Contrary to those studies, Murray et al. (1989) reported that pork from Nn pigs was redder (higher a* value) than pork from NN pigs, and even though Sutton et al. (1997) reported that the LM from Nn pigs had higher drip loss percentages and received
lower color and firmness scores than NN pigs, they failed to find a difference in CIE L*, a*, and b* values, as well as LM moisture and marbling content, between the two genotypes. Still other studies have shown that the pork quality attributes of Nn pigs were quite similar to those of NN pigs (De Smet et al., 1996; Murray and Johnson, 1998; Pommier et al., 1992; Sather et al., 1991b; Tam et al., 1998). The pH of the LM was not affected (P . 0.10) by inclusion of MM in the diets of growing finishing pigs (Table 4). Even though Apple et al. (2000) failed to denote a difference in the ultimate pH of the LM from long-term supplementation of swine diets with MM, Otten et al. (1992) reported that long-term supplementation of swine diets with Mg fumarate effectively elevated muscle pH. Additionally, several authors have reported that feeding diets fortified with Mg, or giving intravenous injections of Mg, shortly before harvest increased initial and / or ultimate muscle pH (Campion et al., 1971; D’Souza et al., 1998, 1999, 2000; Schaefer et al., 1993). It is not unusual for ultimate muscle pH values to be virtually alike in both PSE and normal muscle, but 45-min pH values are critical to the development of PSE pork. Thus, the lack of a discernable difference in the ultimate
Table 5 Effect of halothane genotype and magnesium mica level on the frequency (%) of American a and Japanese b color scores Halothane genotype c
American color scores 1 2 3 4
NN
Nn
0.00
1.25
2.50
0.00 5.56 18.52 13.88
12.03 25.93 21.30 2.78
3.70 12.04 14.81 2.78
3.70 9.26 9.26 10.19
4.63 10.19 15.74 3.70
0.93 12.04 22.22 2.78
18.52 31.47 12.04 0.00
6.48 15.74 11.11 0.00
7.41 10.18 13.89 0.93
5.56 17.59 9.26 1.85
d,e
Japanese color scores f,g 1 2 3 4 a
Magnesium mica (%)
American color score: 1 5 pale pinkish gray and 6 5 dark purplish red (NPPC, 1999). Japanese color score: 1 5 pale gray and 6 5 dark purple (Nakai et al., 1975). c NN 5 halothane-negative pigs and Nn 5 halothane-carrier pigs. d Chi-Square statistic for halothane genotype 5 30.981 (P , 0.001). e Chi-square statistic for magnesium mica level 5 8.971 (P , 0.175). f Chi-square statistic for halothane genotype 5 28.22 (P , 0.001). g Chi-square statistic for magnesium mica level 5 5.468 (P , 0.485). b
J.K. Apple et al. / Livestock Production Science 76 (2002) 103 – 113
pH of the LM from pigs fed MM is neither surprising nor unexpected. Supplementation of swine diets with MM had no effect (P . 0.10) on drip loss percentages and moisture contents of the LM (Table 4). Results of the present study confirm previously published information from our laboratory that long-term supplementation of swine diets with MM did not affect LM drip loss or moisture content (Apple et al., 2001). Moreover, Otten et al. (1992) failed to denote an effect of long-term supplementation of swine diets with Mg fumarate on the water-holding capacity of pork LM. However, feeding diets supplemented with Mg aspartate or Mg sulfate significantly reduced drip loss percentages, even when fed for only 2 days prior to slaughter (D’Souza et al., 2000). Moreover, inclusion of supplemental Mg for 5 days before harvest significantly lowered drip loss in the LM of pigs heterozygous for the halothane-gene (D’Souza et al., 1998, 1999; Schaefer et al., 1993; Schmitten et al., 1984) and heterozygous for the RN gene (Hemann et al., 2000). Both subjective color scores and objective color measurements of the LM were similar (P . 0.10) among carcasses from pigs fed 0.0, 1.25 and 2.50% MM (Table 4). Moreover, dietary MM had no effect (P . 0.10) on the percentage of carcasses with color scores characteristic of PSE pork (Table 5). Neither O’Quinn et al. (2000) nor D’Souza et al. (1999) found a difference in pork color among pigs fed diets containing supplemental Mg. On the other hand, D’Souza et al. (1998) reported lower L* values, and Schaefer et al. (1993) reported higher a* values, for LM chops from pigs supplemented with Mg aspartate 5 days before slaughter. Similarly, the percentage of PSE, or PSE-like, carcasses was greatly reduced by the short-term (D’Souza et al., 1998, 2000) or long-term (Apple et al., 2000) Mg supplementation.
4. Conclusions Data from the present study supports the tenet that pork from Nn pigs was inferior in quality attributes, having had a higher percentage of carcasses with quality traits characteristic of PSE pork. However, inclusion of MM in the diets of growing-finishing
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swine had no appreciable effects on pork quality or on the percentage of carcasses deemed PSE. The lack of any discernable effect of MM on pork quality may be due to two pre-eminent factors: (1) the bioavailability of Mg from MM (which is largely unknown in swine), and / or (2) length of supplementation. Even though results of the present study support the notion that short-term, rather than long-term, Mg supplementation is apparently more effective in improving pork quality, the formulation / production, transportation, and distribution of specialized diets containing elevated levels of Mg for only the last 5 to 7 days of the finishing period may not be a practical, and economically feasible, management step, especially in large, integrated production systems. Inclusion of MM, an inexpensive source of Mg, in starter, grower and / or finisher diets may be more easily incorporated into pre-existing management practices. Moreover, the small economic benefits realized from moderate improvements in feed efficiency and lower diet costs (Apple et al., 2000) makes the long-term MM supplementation an attractive management decision for today’s integrated swine industry. Even though MM supplementation had no beneficial, or deleterious, effects on pork quality in this study, results from this study indicate a need for additional research, specifically whether a shorter duration of MM-supplementation (in particular during the finishing period only) would be more effective in improving pork quality compared to the long-term supplementation program utilized in the present study.
Acknowledgements The authors wish to express their appreciation to Micro-Lite Inc., Chanute, KS, for donation of the magnesium mica and partial financial support of this project. Additionally, the authors fully acknowledge the assistance of Ben Wheeler and the Research and Development staff of Seaboard Farms Inc. in carcass data collection and loin procurement. Finally, the authors wish to thank Ashley Hays, Lance Kirkpatrick, Dari Brown, Ellen Davis, and Joe Leibbrandt for animal care, and Jerry Stephenson, Jennifer Leach, Rebecca Miller, Nicholas Simon, and Joel
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Reiman for assistance in loin fabrication and pork quality data collection.
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