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ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
* Department of Animal Sciences, University of Illinois, Urbana 61801; and
and
Empresa Brasileira de Pesquisa Agropecuaria 89700-000, Concordia, SC, Brazil
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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Key Words: Acid-Base Equilibrium • Feed Withdrawal • Glycolytic Potential • Handling • Pigs
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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; Hamilton, 2002), which has been associated with the occurrence of fatigued and dead pigs during transportation (Ivers et al., 2002a,b). In addition, the level of glycogen reserves in muscle is a major factor determining the extent of postmortem muscle pH decline. High muscle glycogen levels at slaughter result in pork with low ultimate pH, which has pale color and decreased water-holding capacity (Monin and Sellier, 1985; Hamilton et al., 2002). Feed withdrawal before slaughter has been shown to have a variable effect on muscle glycogen reserves. Jones et al. (1985) and Wittman et al. (1994) reported a reduction of muscle glycogen with 24 to 48 h of fasting, but Bidner et al. (2004) did not find any effect after 60 h of fasting. Handling under simulated commercial conditions (Fernandez et al., 2002) and exercise (Henckel et al., 2002) resulted in a degree of glycogen depletion in muscle similar to minimal handling, but adrenaline administration resulted in a greater depletion of muscle glycogen (Henckel et al., 2002). This finding is important, considering that physical exercise and stress induce adrenaline release (Bhagavan, 1992). In addition, Fernandez et al. (1995) showed an interaction between fasting and mixing of pigs; 4 h after mixing with unfamiliar pigs, muscle glycogen was decreased in fasted but not in fed animals. Whether the greater decrease in glycolytic potential in fasted pigs is a result of higher depletion during handling or lower replenishment during the recovery period has not been established. Therefore, this study was conducted to evaluate the effect of feed withdrawal and handling intensity on blood acid-base responses and changes in muscle glycolytic potential in slaughter-weight pigs. |
Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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The protocol for this study was approved by the Institutional Animal Care and Use Committee of the University of Illinois. The study was carried out as a randomized complete block design with a 2 x 2 factorial arrangement of treatments: 1) feed withdrawal (0 vs. 24 h); and 2) handling intensity (low vs. high).
Animals
Sixty pigs (initial weight 107.7 ± 0.56 kg) that were the progeny of line 337 sires mated to C22 dams (Pig Improvement Co., USA, Franklin, KY) were used. Barrows (n = 44) and gilts (n = 16) were distributed equally across the treatments. To allow time for the animals to acclimate to the study environment, pigs were allotted to a treatment on the basis of BW and gender 2 wk before the feed withdrawal treatment was applied. The study was carried out in three blocks over time, with 20 animals in each block.
Housing, Feeding, and General Procedures
The study was carried out in an environmentally controlled finishing building located at the Swine Research Center at the University of Illinois. Pigs were housed in mixed-gender groups of five in pens with part-solid, partially slotted floors, which provided a floor space allowance of 0.95 m2/pig. The facility was mechanically ventilated with thermostatic control, ventilation fans, and space heaters for ambient temperature control. Pigs were given ad libitum access to a standard corn-soybean meal diet, which was formulated to meet or exceed the nutrient requirements for pigs from 80 to 120 kg live weight recommended by NRC (1998).
Two weeks after allotment, starting at 0600, pigs were weighed, a LM biopsy sample was collected, and feed was withdrawn from the pigs on the feed withdrawal treatment. Twenty-four hours after the start of feed withdrawal, rectal temperature was recorded and a blood sample was collected for assessment of baseline values. Two hours after the baseline measurements, pigs were subjected to the handling treatment. Immediately after the handling treatment, rectal temperature was recorded, and a blood sample and a LM biopsy sample were collected. Four hours after the handling procedure, BW was recorded and a third muscle biopsy sample collected. Pigs were restrained by a nose snare for approximately 30 s during the bleeding process but were unrestrained during the biopsy procedure.
Handling Procedure
The handling procedure consisted of moving the pigs individually through a facility (12.20 m long x 0.91 m wide) for eight laps. Pigs subjected to the high-intensity handling treatment were stimulated to move with an electric goad two times per lap. In the low-intensity handling treatment, pigs were moved at their own pace using a paddle and a handling board. The low- and high-intensity treatments were carried out alternately in sequence to avoid bias related to changes in handler and environmental conditions.
Rectal Temperature Measurement and Blood and Biopsy Sampling
Rectal temperature was measured using a digital thermometer (GLA Agricultural Electronics, San Luis Obispo, CA). Two venous blood samples were collected via venipuncture of jugular into either lithium heparinized Vacutainer tubes or Vacutainer tubes with no additive (BD, Franklin Lakes, NJ). Within 5 min of collection, blood samples from the lithium-heparinized tubes were assayed for glucose, lactate, pH, bicarbonate, base excess, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), total carbon dioxide (tCO2), and saturation of oxygen (sO2) using a portable clinical analyzer (i-STAT Corp., Princeton, NJ). Samples collected in the tubes with no additive were allowed to stand until separation of serum occurred and were then centrifuged at 2,000 x g for 15 min. Serum was transferred to microcentrifuge tubes and stored at –20°C for approximately 4 wk until required for analysis of free fatty acid content, which was carried out using a kit for an enzymatic colorimetric method (Sigma Diagnostics, St. Louis, MO).
Biopsy samples were collected from LM for determination of glycolytic potential using a spring-loaded biopsy instrument with B7 cannulas (Biotech PB-U, Nitra, Slovakia); the diameter of the biopsy cannula was 7 mm, and it was set to penetrate 5.0 cm. No anesthetic was used. The first sample (taken at the beginning of feed withdrawal) was collected at the level of the last rib on the left side of the animal, the second sample (taken immediately after the handling procedure) was collected at the level of the last rib on the right side of the animal, and the third sample (taken 4 h after the handling procedure) was collected 10 cm anterior to the last rib, on the right side of the animal. All biopsy samples were collected within the range of minimal intraloin variation for glycolytic potential (from the 10th to last rib) as shown by Bertol (2003). In addition, Bertol (2003) showed that repeated biopsy sampling at the sites used here had no effect on muscle glycolytic potential. After collection, muscle samples were trimmed of skin, fat, and connective tissue, and immediately frozen in liquid N2. Samples were stored at –80°C and freeze-dried before analysis.
Glycolytic Potential
Details of the preparation of biopsy samples, as well as the determination of glycogen+glucose+glucose-6-phosphate combined and lactate have been described by Hartschuh et al. (2002). The assay for glycogen+glucose+glucose-6-phosphate was a modification of the method described by Keppler and Decker (1974). Sigma Diagnostics Kits (Kit 826-A, Sigma Diagnostics) were used for lactate assays. Calculation of glycolytic potential (GP) was according to the formula from Monin and Sellier (1985):
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Statistical Analyses
Analysis of variance was carried out using the PROC GLM procedure of SAS (SAS Inst., Inc., Cary, NC) for a randomized complete block design. The pen was the experimental unit for all variables. The model included the effects of block, feed withdrawal, handling intensity, and the feed withdrawal x handling intensity interaction. For variables that differed among treatments (P < 0.05), means were compared using Student t-test. Paired t-tests were used for comparison of time of measurement within the same treatment (i.e., baseline vs. posthandling measurement). Glycolytic potential was analyzed using the PROC MIXED procedure of SAS for repeated measures.
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Results and Discussion |
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Effects of Feed Withdrawal
The weight of pigs on the fed and fasted treatments was similar at the start of the feed withdrawal period; however, fasted pigs were approximately 5 kg lighter than fed pigs (P < 0.001) at the end of the feed withdrawal period (Table 1).
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), but the increase in rectal temperature during the handling treatment was similar for the two feed withdrawal treatments (Table 3). The decrease in body temperature in fasted animals was likely associated with lower circulating concentrations of thyroid hormones (Becker et al., 1989; Buonomo and Baile, 1991) and with a lower heat increment of feeding.
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). In addition, there was no effect of feed withdrawal on the change in these measurements during the handling treatment (Table 3). These results agree with those of Fernandez et al. (1995), who reported no effect of feed withdrawal on blood lactate concentration in rested and stressed pigs. However, the results of the current study differ from the findings of Schaefer et al. (1987), who reported increased resting levels of blood bicarbonate, base excess, and tCO2 in pigs fasted for 24 h. Baseline pO2 and pCO2 were lower (P < 0.05) in fasted than in fed pigs (Table 2); however, values after the handling treatment were not affected by the feed withdrawal treatment. Lower pO2 values in pigs fasted for 24 h also were reported by Schaefer et al. (1987). Baseline and posthandling blood glucose concentrations were lower (P < 0.05) and serum free fatty acid concentrations were greater (P < 0.01) in fasted than in fed pigs (Table 2); however, the increase in blood glucose and free fatty acids during the handling treatment was similar in fed and fasted animals (Table 3). Fernandez et al. (1995) reported a stress-induced increase in blood glucose in fed animals. In the present study, the magnitude of the response of baseline glucose concentrations to fasting, although statistically significant, was relatively low. The results of the current study show that despite the lower baseline blood glucose and higher free fatty acids in fasted pigs, blood lactate and pH values after handling were not affected by 24-h feed withdrawal. Therefore, it seems likely that the energy substrates used by the muscle during handling were similar in fed and in fasted pigs.
Concerns regarding the blood sampling procedures used here are that the approach used to restrain the animal during sampling or the repeated sampling at relatively short intervals (2 h) could influence the values for the acid-base variables measured. Certainly, using snares to restrain the animal during sampling imposes a stress on the pig. Nonetheless, in the current study, baseline values for measures such as lactate, pH, bicarbonate, and base excess were similar to values obtained in studies that used indwelling jugular catheters for blood sampling (van der Wal et al., 1986; Bickhardt and Wirtz, 1987) or jugular venipuncture (Haydon et al., 1990; Bertol et al., 2002, 2005), which suggests that the blood sampling method used in this study produced blood acid-base values similar to other approaches. Moreover, in previous studies where gentle handling of animals has been used, the change in blood acid-base measures between samples taken 2 h before and immediately after the handling treatment has been limited (Hamilton et al., 2004), suggesting a limited effect of blood sampling at 2-h intervals on blood acid-base measures.
In the current study, the effect of feed withdrawal on muscle glycolytic potential can only be evaluated in association with the handling treatment (Table 4). To minimize the number of samples taken from each animal, a biopsy sample was not taken at the end of the feed withdrawal treatment period. There was a feed withdrawal treatment x sampling time interaction for glycolytic potential (P < 0.01). Longissimus muscle glycolytic potential values did not differ between fed and fasted animals at the beginning of the feed withdrawal treatment (Table 4); however, the combination of the fasting and the handling treatment resulted in lower (P < 0.05) muscle glycolytic potential immediately after handling. In addition, compared with baseline values, the muscle glycolytic potential of fasted pigs was 16.3 and 12.7% lower (P < 0.05) than that of fed pigs immediately and 4 h after the handling treatment, respectively (Table 4). In contrast, in fed pigs, muscle glycolytic potential was similar among sampling time points (Table 4). The total fasting time at the end of the handling procedure was between 26 to 30 h (including the period of baseline evaluation and handling). The decrease in glycolytic potential in fasted pigs in the present study is in line with the reports of Jones et al. (1985) and Wittman et al. (1994). With a similar time of feed withdrawal (24 h), Wittman et al. (1994) showed a decrease of 19.2% in LM glycolytic potential. In addition, Jones et al. (1985) reported 30% less glycogen content in the LM of pigs fasted for 41 h. In contrast, Warriss (1982) did not find any change in glycogen content of the semi-membranosus muscle after 26 h of feed withdrawal, but showed a decrease (38%) in pigs fasted for 48 h. Fernandez et al. (1995) showed that 4 h after mixing unfamiliar pigs for 30 min, LM glycogen content was decreased in fasted but not in fed pigs, which is similar to the findings of the current study.
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Effect of Handling Intensity
The handling intensity treatment had no effect on live weight or growth performance at any stage during the study (Table 1). Handling intensity would not be expected to affect measurements taken before the application of this treatment.
There was no effect of handling intensity on either posthandling rectal temperature or the change in temperature during handling (Tables 3 and 5). Baseline values for lactate were less (P < 0.05) for the high-than for the low-intensity treatment. This result was unexpected and is probably due to chance as baseline measurements were taken before the handling treatment was imposed.
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). In addition, the magnitude of change in these measurements during handling was more extensive in pigs submitted to high- than to low-intensity handling (Table 3). Similar effects of physical exercise or handling of different intensities on blood acid-base balance measurements have been observed previously (van der Wal et al., 1986; Bertol et al., 2002; Hamilton, 2002). High concentrations of lactic acid and decreases in blood bicarbonate, the main extra-cellular buffer, are responses characteristic of metabolic acidosis as described by Bhagavan (1992).
Posthandling values for pO2 and sO2 were similar to prehandling values for both handling treatments (Table 5). Blood levels of pO2 and sO2 are indicators of the amount of oxygen available to the tissues. Blood pCO2 increased (P < 0.05) during handling in the high- but not the low-intensity handling treatment (Table 3). However, the increase in posthandling blood pCO2 levels was relatively limited, suggesting that the lower blood pH resulting from the high-intensity handling was caused mainly by lactic acid production in response to physical exercise and stress (Pruden et al., 1994), rather than by changes in respiration. Decreases in bicarbonate, base excess, and tCO2 induced by handling are a consequence of the buffering action of the bicarbonate system to neutralize increases in lactate (Pruden et al., 1994). The considerable increase in blood lactate concentrations in pigs submitted to high-intensity handling is related to the limited increase in oxygen utilization due to the limitation of rates of blood flow, respiration, and oxygen delivery to the tissues (Bhagavan, 1992). These effects, associated with an increased demand for energy and high circulating glucose levels, result in an increase in anaerobic metabolism of glucose to generate energy. During intense exercise, anaerobic metabolism becomes essential to supply the energy demand for muscle activity, with a resultant increase in glycogen degradation, glucose uptake, and lactate release by the muscle (Hocquette et al., 1998).
Blood glucose concentrations were greater (P < 0.01) posthandling than baseline in both the low- and high-intensity handling treatments (Table 5). Stress-induced increases in blood glucose have been demonstrated previously in pigs (Fernandez et al., 1995; Rosochacki et al., 2000). In situations that involve stress and/or high intensity exercise, catecholamines are important determinants of glucose mobilization (Bhagavan, 1992).
There was no effect of handling intensity on LM glycolytic potential measured at any time during the study (Table 4). Other studies have shown a decrease in muscle glycolytic potential associated with handling of pigs. For example, Henckel et al. (2002) reported a similar reduction in muscle glycogen for pigs submitted to minimal stress or to 10 min exercise (average 11.7%). In addition, handling under simulated commercial conditions resulted in a depletion of muscle glycogen (average 29%) compared with minimal stress (Fernandez et al., 2002). Similarly, Rosochacki et al. (2000) reported that immobilization stress for 15 min induced a 27% decrease in muscle glycogen content. By comparison, the period of immobilization for blood sampling in the current study was relatively short, lasting on average less than 30 s. In the present study, there was a numerical decrease in glycolytic potential in the samples taken after the handling model compared with those taken at the beginning of the feed withdrawal treatment but the differences between the means was not statistically significant (Table 4). This suggests that a longer period of exercise than used in the present study (approximately 5 min) is required to decrease muscle glycolytic potential levels. Further research is needed to determine the extent of muscle glycolytic potential changes during longer periods of handling under fasted and fed conditions, as well as the relationship between muscle glycolytic potential and posthandling resting periods.
Overall, results of this study highlight the major effect of animal handling intensity on blood acid-base status and, particularly, the negative effect of high-intensity handling. Withdrawing feed from pigs for 24 h had limited effects on blood acid-base status, but it decreased muscle glycolytic potential and rectal temperature. Decreased glycolytic potential and body temperature in the live animal at slaughter may result in improved color and water-holding capacity in postmortem muscle.
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Footnotes |
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2 Correspondence: 216 Animal Sciences Laboratory, 1207 W. Gregory Dr. (phone: 217-333-6455; fax: 217-333-7861; e-mail:mellis7{at}uiuc.edu).
Received for publication September 29, 2004. Accepted for publication March 30, 2005.
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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