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Department of Animal and Range Sciences, South Dakota State University, Brookings 57007
2 Correspondence:
(Phone: (605) 688-5451; fax: (605) 688-6170; E-mail:
duane_wulf{at}sdstate.edu).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Key Words: Exercise • Fasting • Glycogen • Meat Quality • pH • Transport
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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One hundred sixty-two barrows and 15 gilts of two different genetic sources were housed in 12 pens (15 pigs per pen) in a 1,000-pig commercial confinement finishing facility. All pigs were weighed individually 3 d prior to transport, and their average BW was 116.4 kg. Genetic source A (AGS) pigs were reputed to be Rendement Napole gene and Halothane gene negative genetics that produce high quality pork, while genetic source B (BGS) pigs were reputed for high lean growth genetics. A 2 x 2 x 3 factorial design was used for this study, which involved two genetic sources, fasting (F) or no fasting (N) of pigs 48-h prior to harvest, and three different transport times (0.5, 2.5, or 8.0 h) on the semitrailer to the packing plant. Two pens of pigs were assigned to each treatment. Pens were assigned, so there was approximately an equal distribution of genetic sources and sex classes in each treatment. All experimental procedures were approved by the South Dakota State Institutional Animal Care and Use Committee.
Transport
Pigs were transported from the hog facility to the packing plant in a commercial potbelly semitrailer. The area of each semitrailer compartment was determined. Pigs were loaded according to treatment and sorted so each pig would be allowed 1.3 m2 in their respective semitrailer compartment. There were three different loading times. Pigs from treatments F8.0 and N8.0 were loaded at 0530, pigs from treatments F2.5 and N2.5 were loaded at 1045, and pigs from treatments F0.5 and N0.5 were loaded at 1245. The truck traveled on two-lane highways only, resulting in the truck’s changing speeds, stopping, and starting periodically. Average hog barn temperature and humidity, along with average outside temperature, humidity, and barometric pressure were 19.3°C, 65.7%, -10.7°C, 66.3%, and 77.1 torr, respectively. Additionally, the number of pigs in the truck that were lying down was recorded periodically. At 3 h, 5 h, and 7 h of transport the number of pigs lying down was three, four, and three, respectively.
Packing Plant
The truck arrived at the packing plant at 1320. Pigs were unloaded in the opposite order that they were loaded at the hog facility. Therefore, the F0.5 and N0.5 treatments were unloaded first. Each lot of pigs was weighed and treatment weight averages were calculated. All pigs were unloaded by 1415 and allowed to rest for 2 h prior to harvest. Two pigs were injured during transport and, consequently, were removed from the study upon arrival at the packing plant. Additionally, the data of 15 pigs were lost during the chilling process at the packing plant and five samples were removed from the study due to lack of identity after the boning and packaging process was complete. As a result, 155 boneless loins remained in the study for further meat quality testing. The number of observations for meat quality traits in each treatment ranged from 23 to 32 and are shown in Table 3
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Percent lean was determined on the warm carcasses before chilling by a Fat-O-Meater S71 (SFK Technologies, Hvidovre, Denmark), which measures 10th rib fat depth and loin muscle depth. Temperature and pH were measured at 24 h postmortem in the semimembranosus (SM) and longissimus lumborum muscles of the right side of each carcass using a Meatcheck 160 pH (Sigma Electronic GmbH Erfurt, Erfurt, Germany), equipped with a Mettler-Toledo pH probe LoT406-M6-DXK-S7/25 (Mettler-Toledo, GmbH, Hackacker, Germany). Backfat thickness was measured at the last rib. Loins from the left side of each carcass were removed, boned, vacuum packaged, and taken to the South Dakota State University Meat Laboratory for meat quality testing.
Purge Loss
At 7 d postmortem, vacuum packaged boneless loins were weighed (initial weight) to the nearest 0.1g, removed from their bag, and allowed to drip for 15 min. The average dry bag weight was determined and subtracted from the initial loin weight. After 15 min of drip-time the loins were reweighed to the nearest 0.1g, and percent purge loss was determined as a percentage of initial loin weight.
Sample Fabrication
Following purge loss determination, chops were removed from the longissimus lumborum starting at the cranial end and continuing towards the caudal end for glycolytic potential assay (one 20-g chop) and drip loss (one 2.5-cm-thick chop). The remaining longissimus lumborum was vacuum packaged and stored at -18°C for cooking loss and Warner-Bratzler Shear determination.
Glycolytic Potential Analysis
A 20-g chop was removed from each longissimus lumborum at 7 d postmortem, placed in a whirl pack bag, and stored at -20°C. Chops were allowed to thaw at 1.4°C for 12 h prior to beginning the glycolytic potential (GP) assay. One gram of each longissimus lumborum was extracted to determine GP, as described by McKeith et al. (1998). Perchloric (0.6 N) acid was used to deproteinate the muscle samples. The resulting perchloric extracts were used to quantify glycogen, glucose, glucose-6-phosphate (GGG), and lactate. Glycolytic intermediates were catalyzed to glucose-6-phosphate using 5 µL of hexokinase and then into 6-phosphogluconate in the presence of NADP+, which was reduced to NADPH and the absorbance measured spectrophotometrically at 340 nm. Lactate was measured by adding excess NAD+ in a glycine and hydrazine buffer solution with lactate dehydrogenase, resulting in NADH being formed. Differences in absorbance were measured at 340 nm. Glycolytic potential was expressed as micromoles of lactate per gram of wet muscle and determined by [2 x (glucose + glycogen + glucose-6-phosphate)] + lactate.
Color, Firmness, Marbling, and Drip Loss
One 2.5-cm-thick chop was removed from each loin at 7 d postmortem. External fat and secondary muscles were removed, and each chop was weighed to the nearest 0.01 g. Color, firmness, and marbling were assessed using NPPC Quality Standards (NPPC, 1999). In addition, L*, a*, and b* color values were measured using a Minolta Chroma Meter CR-310 (Minolta Corp., Ramsey, NJ) set at D65 illuminant. Each chop was retail wrapped on a styrofoam tray, arranged at an approximate 30° angle to allow the exudate to flow away from the chop, and placed in a well-lit cooler at 1.4°C (simulation of retail case) for 24 h. After 24 h chops were removed from their package and exudate and reweighed to the nearest 0.01 g. The amount of drip loss was determined as a percentage of initial weight.
Cooking Loss and Warner-Bratzler Shear Force
Two 2.5-cm-thick chops were removed from the cranial end of each frozen loin section. Chops were vacuum packaged and allowed to thaw at 1.4°C for 24 h prior to cooking. Chops were cooked in an impingement oven (Lincoln Foodservice Products, Inc., Ft. Wayne, IN) set at 190°C for 11 min resulting in an average final internal temperature of 65.8°C ± 6.5°C. This final internal temperature is lower than the 71°C recommended by AMSA (1995). Our preliminary trials had shown that these oven settings (190°C for 11 min) resulted in an average final internal temperature of 71°C ± 3°C, but for some unknown reason, the average final internal temperature in this study was lower and more variable. The chops were weighed raw (prior to cooking) and again after cooking to the nearest 0.01 g; cooking loss was determined and expressed as a percentage of initial raw weight. After chops cooled to room temperature, three 1.27-cm diameter cores were taken from each chop (six cores per pig) parallel to the muscle fiber orientation. Peak shear force was measured, once on each core, using a Warner-Bratzler shear force machine.
Statistical Analysis
All continuous data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). All continuous data were analyzed as a completely randomized design (experimental unit = pig) with genetic source (2 levels; A or B), fasting (2 levels; 0 or 48 h), and transport (3 levels; 0.5, 2.5, and 8 h), serving as the main effects in the model, along with all three two-way interactions. The three-way interaction was analyzed but was not significant for any trait and thus removed from the statistical model. With data from all pigs included, GP residuals were not normally distributed (P < 0.0001). Three pigs had GP residuals greater than 3.00 standard deviations above the mean. Additionally, when the GP residuals were added to the GP mean for nonfasted, 0.5-h treatment, these three pigs had adjusted GP values greater than 190 µmol lactate/g. Emnett et al. (2002) established a threshold GP value of 160 µmol lactate/g, above which pigs are considered to be Rendement Napole gene positive. Therefore, we assumed these three pigs to be Rendement Napole gene positive and excluded their data from the analysis of all muscle quality traits, resulting in a normal distribution of GP residuals. Least squares means were calculated for all variables and separated using pairwise t-tests. All frequency data were analyzed using chi-square.
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Results |
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It was impossible to test for statistical differences among treatments for live weight and dressing percentage because these traits were measured by pen, resulting in no replication and leaving no degrees of freedom for the error term. Although this was not the main focus of the study, the live weights and dressing percentages are shown in Table 1. Fasting pigs for 48-h preharvest decreased hot carcass weight (HCW) (P < 0.05), but length of transport did not affect HCW (P > 0.05) (Table 1). Neither fasting nor transport time had an effect on 10th-rib fat depth, loin muscle depth, or percent lean (P > 0.05), which is consistent with earlier findings by Bowland and Standish (1966), Fausch et al. (1968), and Jones et al. (1985).
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. Fasting pigs for 48 h prior to harvest had no effect on GP, GGG, lactate, SM pHu, firmness, and shear force. Pigs that were fasted compared to pigs that were not fasted had higher LD pHu, darker-colored lean, higher marbling scores, and improved water-holding capacity. The frequency of pale (color score 1 or 2), normal (color score 3 or 4), and dark-colored (color score 5 or 6) pork between fasted pigs and nonfasted pigs was not different (P = 0.337) (Figure 1).
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. Meat from pigs that were transported 8.0 h had lower GP and lactate, higher LD and SM pHu, darker lean color, lower L*, lower 7-d purge loss, lower 24-h drip loss, lower cooking loss, and lower shear force values than meat from pigs transported 0.5 h (P < 0.05). Meat from pigs transported 2.5 h had higher LD and SM pHu, lower L*, lower 7-d purge loss, lower 24-h drip loss, and lower cooking loss than meat from pigs transported 0.5 h (P < 0.05). Meat from pigs transported 8.0 h had lower lactate, higher LD pHu, higher color scores, lower L*, and lower cooking loss than meat from pigs transported 2.5 h (P < 0.05). As length of transport increased, the frequency of pigs that produced pale-colored pork decreased, and the frequency of pigs to produce dark-colored pork increased (P < 0.001) (Figure 2). Meat quality traits that were significantly affected by both fasting and length of transport showed a greater difference between 0.5-h and 8.0-h transport than between fasted and nonfasted pigs. In general, transportation affected meat quality to a greater extent than fasting.
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Semimembranosus pHu, L*, color score, and drip loss were the only traits where the fasting x transport interaction was significant (P < 0.05) (Table 3). Fasting improved SM pHu, L*, color score, and drip loss (P < 0.05) for pigs that were transported 0.5 h, but when pigs were transported for 2.5 h or 8.0 h, fasting had little or no effect on these muscle quality traits. The fasting x transport interaction was not significant (P > 0.05) for GP, GGG, lactate, 24-h LD pHu, and purge loss indicating the fasting and transport effects were independent and additive for these traits.
Genetic Effects
Pigs from AGS were reputed to be Rendement Napole Gene and Halothane Gene-free genetics that produce high-quality pork, while pigs from BGS were reputed for high lean growth. The carcass and quality characteristics of pigs from AGS and BGS are presented in Table 4. There were no differences (P > 0.05) in HCW or loin depth between pigs from AGS vs BGS. Pigs from BGS had less backfat and a higher percent lean (P < 0.05) than the pigs from AGS. The longissmus dorsi (LD) muscle from AGS had lower GP, lower lactate, less purge loss, less drip loss, less cook loss, and lower shear force values, along with a higher 24-h LD pH and higher subjective color, firmness, and marbling scores than samples from BGS. There was an obvious difference in the genetic sources, and the results from this study confirm that AGS pigs produced higher quality pork than BGS pigs.
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. Fasting pigs from AGS reduced GP and lactate, increased LD pHu, lowered L*, and reduced cook loss (P < 0.05); however, fasting pigs from BGS did not change GP, lactate, LD pHu, L*, or cook loss (P > 0.05) (Table 5). The genetic source x transport interaction was significant for tenth rib fat and percent lean as shown in Table 5. Pigs from AGS that were transported for 2.5 h had less tenth rib fat and a higher percent lean (P < 0.05) than the pigs from AGS that were transported for 0.5 h. However, length of transport did not effect tenth rib fat depth or percent lean in pigs from BGS (P > 0.05) (Table 5). Fasting lowered GP, lactate, and LD pHu in pigs from AGS (a genetic source that had high initial pork quality), while fasting had no effect on pigs from BGS (a genetic source with lower initial pork quality). Increased transport times resulted in lower GP and higher LD pHu regardless of genetic source.
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Discussion |
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This study showed that fasting pigs causes a reduction in hot carcass weights. These results agree with the findings of Warriss (1982), Jones et al. (1985), and Becker et al. (1989).
Effects of Fasting
Consumed carbohydrates are the main source of glucose in the blood (Guyton and Hall, 1996). Insulin works to store excess blood glucose as glycogen in the muscle or liver or as adipose tissue. Of the glycogen stores in the liver and muscle, the glycogen stored in the liver is more readily available for glycogenolysis because the enzyme glucose-6-phosphotase is present in liver but not in muscle (Mathews and Van Holde, 1995; Murray et al., 2000). Sugden et al. (1976) showed that in terms of total loss of glycogen from liver plus carcass in rats, liver contributed 64% and the carcass 36% during deprivation of food for 19 h. The corresponding values over a 43-h food withdrawal were 61% for liver and 39% for the carcass (Sudgen et al., 1976). Previous livestock studies showed that fasting swine or bovine lowered muscle glycogen (Jones et al., 1985; Warriss et al., 1987) and increased meat pH (Warris, 1982; Crouse et al., 1984; Eikelenboom et al., 1991). The current study showed that pigs that were fasted had higher LD pHu, and darker-colored lean, higher marbling scores, and higher water-holding capacity than pigs that were not fasted (Table 2). Visual marbling scores may have been higher in fasted pigs than notfasted pigs due to greater color contrast between fat and lean caused by the darker colored lean in fasted pigs (Wulf et al., 2002).
Effects of Transport
Neither fat nor blood glucose is a primary energy source at high exercise intensities; thus, muscle glycogen is the most readily available and easily metabolized fuel for exercise (Buchbinder et al., 1987; Murray et al., 2000). There have been many swine exercise studies conducted to try to improve pork quality (Lewis et al., 1989; Enfalt et al., 1997; Petersen et al., 1997). However, these studies did not show improvement in pork quality attributes or a decrease in muscle glycogen. The probable reason that these studies did not see any effects of exercise on pork quality is because the exercise, which lasted for 56 to 100 d or for the entire finishing period, resulted in trained pigs. A human study conducted by Green et al. (1991) showed extended periods of exercise training caused adaptations in muscle glycogen concentration that were 47.1% higher in the vastus lateralis muscle after 10 to 12 d of training. Training resulted in a persistently higher concentration of glycogen, but glycogen, still decreased at a similar rate during a single exercise bout (Green et al., 1991). On average muscle glycogen concentration was reduced 20% at 15 min, 30% at 60 min, and 43% by 99 min of exercise (Green et al., 1991).
Briskey et al. (1959) conducted a swine exercise study that involved one period of exhaustive exercise immediately prior to harvest and found exercised hogs produced muscle that had low glycogen concentrations, high pH values, dark color, and low expressible water ratios.
In the pork industry, the most typical form of exercise occurring within the 24 h prior to harvest would be elicited through transporting of pigs on a semitrailer to the packing plant. Therefore, this study involved different lengths of transport on the semitrailer. Becker et al. (1989) reported that transporting and associated handling impose an acute demand on the energy metabolism and fluid regulation of slaughter hogs. The consequence of this demand did not have a detrimental effect on meat quality (Becker et al., 1989). However, in the present study length of transport had a positive impact on pork quality. In general, as transport time was increased, GP, GGG, and lactate decreased, muscle pH increased, pork color became darker, and water-holding capacity increased (Table 2).
Genetic Effects
Pork from AGS had a lower GP and lactate, higher pHu, and more desirable pork quality characteristics than pork from BGS. Pigs from AGS showed a greater response to fasting than pigs from BGS. Fasting may not be an effective method of improving pork quality in pigs with low muscle quality genotypes. Longer transportation times may be the most effective method of lowering muscle glycogen to improve pork quality in pigs with low muscle quality genetics.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Footnotes |
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Received for publication January 29, 2002. Accepted for publication July 10, 2002.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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