J. Anim. Sci. 2005. 83:75-81
© 2005 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Effects of dietary supplementation with L-carnitine and fat on blood acid–base responses to handling in slaughter weight pigs1
T. M. Bertol
,
M. Ellis*,2,
D. N. Hamilton*,3,
E. W. Johnson* and
M. J. Ritter*
* 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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Blood acid–base responses to handling were evaluated in slaughter weight pigs fed diets supplemented with L-carnitine and fat. The study was carried out as a randomized block design with a 2 x 2 factorial arrangement of treatments: 1) dietary L-carnitine supplementation (0 vs. 150 ppm, as-fed basis); and 2) dietary fat supplementation (0 vs. 5%, as-fed basis). Sixty pigs (91.1 ± 5.14 kg BW) were housed in mixed-gender groups of five and had ad libitum access to test diets (0.68% true ileal digestible lysine, 3,340 kcal of ME/kg, as-fed basis) for 3 wk. At the end of the feeding period (110.3 ± 7.52 kg BW), pigs were subjected to a standard handling procedure, which consisted of moving individual animals through a facility (12.2 m long x 0.91 m wide) for eight laps (up and down the facility), using electric prods (two times per lap). There was no interaction between dietary L-carnitine and fat supplementation for any measurement. Pigs fed 150 ppm of supplemental L-carnitine had lower baseline blood glucose (P < 0.05) and higher baseline blood lactate (P < 0.05) concentrations than the nonsupplemented pigs. After handling, pigs fed L-carnitine-supplemented diets had a higher (P < 0.05) blood pH and showed a smaller (P < 0.05) decrease in blood pH and base excess than those fed the nonsupplemental diets. Baseline plasma FFA concentrations were higher (P < 0.01) in pigs fed the 5% fat diet. After the handling procedure, blood glucose, lactate, and plasma FFA were higher (P < 0.05) in pigs fed the 5 vs. 0% fat diets, but blood pH, bicarbonate, and base excess were not affected by dietary fat. The handling procedure decreased (P < 0.01) blood pH, bicarbonate, base excess, and total carbon dioxide and increased (P < 0.01) blood lactate, partial pressure of oxygen, and glucose, and also increased (P < 0.01) rectal temperature. Free fatty acid concentrations were increased by handling in pigs fed both 0 and 5% fat and 150 ppm L-carnitine. In conclusion, dietary L-carnitine supplementation at the level and for the feeding period evaluated in the current study had a relatively small but positive effect on decreasing blood pH changes in finishing pigs submitted to handling stress; however, dietary fat supplementation had little effect on blood acid–base balance.
Key Words: Acid–Base Equilibrium • Carnitine • Dietary Fat • Handling • Pigs
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Introduction
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Animal losses during transport to the slaughter plant and poor meat quality are important issues for all sectors of the pig industry. These two factors are associated with preslaughter handling. Rapid increases in blood lactic acid in pigs can be induced by factors during handling such as physical exercise (van den Hende et al., 1970
), stimulation with electric goads (Bickhardt and Wirtz, 1987), or both (Bertol et al., 2002). Occurrence of nonambulatory pigs has been associated with short-term, acute handling stress and lowered blood pH (Ivers et al., 2002). The metabolic response to short-term handling stress can also compromise meat quality when it occurs immediately before slaughter (Channon et al., 2000). Therefore, approaches that decrease lactate production and the extent of reduction in blood pH during handling are of practical importance. Decreasing the use of glucose and increasing the use of fatty acids as the energy substrate by the muscle is a potential approach to address this problem. L-carnitine acts as a transporter of long-chain fatty acids from the cytosol to the mitochondrial matrix, thereby playing a key role in the use of fatty acids as energy substrate by the tissues (Bhagavan, 1992). There is in vitro evidence that L-carnitine increases fatty acid oxidation to produce energy (Wolfe et al., 1978; Owen et al., 2001a). In addition, the energy source in the diet influences the amount and type of energy reserves in the muscle (Briskey et al., 1960; Rosenvold et al., 2001), and, consequently, can affect both muscle metabolism and the final metabolites produced, particularly in periods of high energy demand (Lapachet et al., 1996). The objective of this study was to investigate the efficacy of dietary fat and L-carnitine supplementation to decrease blood acid–base responses in slaughter-weight pigs subjected to a short-term, acute standard handling procedure.
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Materials and Methods
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Experimental Design
This study was conducted at the Swine Research Center of the University of Illinois. All animal procedures were performed according to the guidelines of and with prior approval from the Institutional Laboratory Animal Care Advisory Committee. A randomized block design with a 2 x 2 factorial arrangement of treatments was used: 1) dietary L-carnitine supplementation (0 vs. 150 ppm, as-fed basis), and 2) dietary fat supplementation (0 vs. 5%, as-fed basis).
Animals
Sixty commercial hybrid pigs (progeny of 355 sires x C22 dams; Pig Improvement Co., USA, Franklin, KY) were assigned to the treatments according to initial BW (91.1 ± 5.14 kg BW) and gender. The experiment was carried out in three blocks over time. Barrows (n = 20) and gilts (n = 40) were distributed equally across treatments.
Diets and Housing
The diets were based on corn and soybean meal and were formulated to meet or exceed the nutrient requirements of NRC (1998) for pigs from 80 to 120 kg live weight (Table 1). Energy, protein, and amino acids levels were maintained constant across treatments by replacing starch by Solka-Floc (Fiber Sales and Development Corp., Green Brook, NJ) and fat in the diets. Diets were kept isocaloric because the objective of this study was to investigate the effect of dietary fat per se and not the effect of dietary energy concentration. After 1 wk of acclimation, during which a standard finishing diet was fed, pigs were given ad libitum access to the experimental diets for 3 wk. Pigs were housed in an environmentally controlled finishing building in mixed-gender groups of five. Pens had part-solid, part-slotted floors, and 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.
At the end of the feeding period, a blood sample was collected (see procedures in a subsequent section) and rectal temperature was measured to establish baseline values. Rectal temperature was measured using a digital thermometer (GLA Agricultural Electronics, San Luis Obispo, CA). Live weight was recorded and LM area and backfat thickness was measured using an Aloka model 500 V B-mode ultrasound scanner fitted with an Aloka 5011 probe (Corometrics Medical Systems, Wallingford, CT) with a transverse scan being taken over the LM at the 10th rib.
Handling Procedure
Two hours after baseline measurements, the pigs were subjected to a standard handling procedure, which consisted of moving the pigs individually through a handling facility (12.2 m long x 0.91 m wide) for eight laps, with one lap consisting of moving the pigs once up and down the facility. Pigs were stimulated to move with an electric prod (two times per lap) and a handling board. Rectal temperature was measured and a blood sample was collected immediately after the handling procedure, which lasted approximately 5 min. The handling procedure for the first two blocks of the study was carried out on the same day in December and that for the third block was carried out on 1 d in March. Mean ambient temperature and relative humidity in the facility where the handling test was conducted was 21.5°C and 55.9% for Blocks 1 and 2, and 19.5°C and 59.0% for Block 3.
Blood Sampling and Analyses
Venous blood samples were collected via venipuncture of the jugular vein into 10-mL lithium heparinized Vacutainer tubes and immediately placed on ice. Blood was analyzed for glucose, pH, lactate, partial pressure of carbon dioxide (PCO2), partial pressure of oxygen (PO2), bicarbonate (HCO3–), total carbon dioxide (TCO2), base excess, and saturation of oxygen (O2S) within 10 min of collection using a portable clinical analyzer (i-STAT Corp., Princeton, NJ). Plasma was obtained by centrifuging the blood at 2000 rpm for 20 min approximately 1 h after blood collection. Plasma was transferred to microcentrifuge tubes and stored at –20°C before being analyzed for FFA and ß-hydroxybutyrate content using an enzymatic colorimetric method (Sigma Diagnostics, St. Louis, MO).
Statistical Analyses
Analysis of variance was carried out using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC) for a randomized complete block design with a 2 x 2 factorial arrangement of treatments. The model used included the effects of block, dietary carnitine level, dietary fat level, and two- and three-way interactions. Data for baseline and posthandling FFA levels were not normally distributed on the basis of the Shapiro Wilkes test (P < 0.01) and were submitted to logarithmic transformation before analysis of variance. Pig was used as the experimental unit for the blood and carcass measurements, and pen was used as the experimental unit for growth performance data. Paired t-tests were used for comparison of different sampling time points within the same treatment.
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Results and Discussion
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There were no interactions between L-carnitine and fat supplementation for any measurement and, consequently, only the results for the main effects are presented.
Effects of Dietary L-Carnitine Supplementation
L-Carnitine supplementation had no effect on growth performance or ultrasound carcass characteristics (Table 2). The findings on growth performance are in agreement with those of Owen et al. (2001a,b), which showed no effect of L-carnitine supplementation on the growth performance of growing-finishing and finishing pigs, respectively. However, both of these studies reported a decrease in backfat thickness at the 10th rib. In addition, Owen et al. (2001a) observed an increase in carcass lean percent in finishing pigs fed diets with up to 125 ppm of L-carnitine from 56 to 120 kg live weight, which is in contrast to the results of the current study, where the pigs were fed 150 ppm L-carnitine for a shorter time period (i.e., 3 wk from approximately 90 to 110 kg live weight).
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Table 2. Effect of dietary L-carnitine and fat supplementation on growth performance and ultrasound carcass characteristics
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Baseline blood glucose concentrations were decreased (P < 0.05) and blood lactate concentrations were increased (P < 0.05) in pigs fed 150 ppm of supplemental L-carnitine compared with the nonsupplemented pigs (Table 3). However, considering the potential for changes in blood lactate and glucose in pigs (Hamilton et al., 2004), the increase in these two metabolites was small and of limited significance. No difference was detected in plasma free fatty acids and ß-hydroxybutyrate concentrations (Table 3), which suggests that no detectable change in resting muscle energy metabolism was stimulated by L-carnitine.
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Table 3. Effect of dietary L-carnitine on baseline and posthandling rectal temperature, blood metabolites, and blood gasesa
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Pigs fed 150 ppm of supplemental L-carnitine had higher posthandling blood pH (P < 0.05; Table 3
) and showed a lower decrease in blood pH (P < 0.01) and base excess (P < 0.05) during handling than the nonsupplemented pigs (Tables 3 and 4). The blood metabolites and gases that can influence blood pH such as lactate, HCO3–, PO2, and PCO2 were not significantly affected during handling by L-carnitine supplementation. However, the treatment difference in posthandling blood pH was relatively small and reflected nonsignificant treatment differences in those blood variables that influence blood pH (Table 4).
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Table 4. Effect of dietary L-carnitine and fat supplementation on the difference between baseline and posthandling values for rectal temperature, blood metabolites, and blood gases
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It has been claimed that dietary L-carnitine increases use of fatty acids and decreases the use of AA as an energy substrate in pigs (Owen et al., 2001a). An increase in fatty acid oxidation during physical exercise is expected because muscle activity increases free fatty acid uptake and inhibits malony L-CoA (Hall et al., 1996). This leads to an increase in the activity of the enzyme carnitine palmitoyl transferase I, resulting in an increased supply of long-chain fatty acids to the mitochondria. In this context, a higher availability of L-carnitine in muscle could further accelerate the importation of long-chain fatty acids into the mitochon-dria, favoring fatty acid oxidation. This potential change in the energy substrate available to the muscle could lead to a decrease in glucose metabolism and the exercise-induced build up of lactate and associated decrease in pH in the muscle. However, no detectable effect of L-carnitine on the products of glucose and fatty acid metabolism during exercise was observed in the current study. It is possible that the relatively short duration of physical exercise used in the current study, which was approximately 5 min on average, was not sufficient to produce the change from glucose to fatty acid metabolism in the muscle. Therefore, these results suggest that, under conditions of short-term, acute handling, the effect of L-carnitine on acid–base balance were of moderate magnitude. Longer-term exercise, such as can occur during the preslaughter period, may yield different results.
Effect of Dietary Fat Supplementation
Dietary fat supplementation had no effect on growth performance or carcass characteristics (Table 2). These results were expected because the diets were formulated to be isocaloric and isoproteic, and feed intakes were similar; thus, the pigs consumed similar amounts of energy and amino acids across the fat treatments.
Inclusion of 5% of fat in the diet increased (P <0.01) baseline concentrations of plasma FFA by 51% (Table 5). Similar responses were observed in rats (Brun et al., 1999) and in humans (Greenhaff et al., 1988) fed high-fat diets. However, Greenhaff et al. (1988) also observed a sharp increase in blood ß-hydroxybutyrate concentrations under resting conditions, which did not occur in the current study. Posthandling concentrations of plasma FFA were 34% higher (P < 0.01) in pigs fed the 5 vs. the 0% fat diet, whereas ß-hydroxybutyrate concentrations showed only a tendency (P = 0.06) to increase with fat supplementation (Table 5). These posthandling differences between the dietary fat treatments largely reflect the differences that were already present in the baseline measurements because the increase in plasma FFA during exercise was similar for the fat treatments (Table 4). Because ß-hydroxybutyrate is a product of oxidation of fatty acids in liver but not in muscle, it is not surprising that blood levels did not change after short-term physical exercise.
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Table 5. Effect of dietary fat supplementation on baseline and posthandling rectal temperature, blood metabolites, and blood gasesa
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Blood glucose concentrations were higher (P < 0.05) after handling and increased (P < 0.05) more during handling in pigs fed the 5 vs. 0% fat diet, whereas the decrease in ß-hydroxybutyrate concentrations during exercise tended to be greater (P = 0.06) in the 0 vs. 5% fat treatment group (Tables 4 and 5). The effect of fat supplementation on blood glucose and plasma FFA changes during exercise is in agreement with the findings of Greenhaff et al. (1988), who observed higher blood glucose and free fatty acid concentrations after short-term, high-intensity exercise in humans fed high-fat, low-carbohydrate diets than in those fed low-fat, high-carbohydrate diets. In addition, Leheska et al. (2002) reported higher blood glucose concentrations in pigs after feeding a high-fat, low-carbohydrate diet for 14 d compared with pigs fed a low-fat, high-carbohydrate diet. The high concentration of blood glucose in pigs receiving the high-fat diet in the current study is possibly due to a decrease in glucose uptake by the cell as a consequence of insulin resistance induced by the elevation of plasma FFA (Clerk et al., 2002), or by inhibition of key enzymes of glycolysis by fatty acid oxidation (Bhagavan, 1992). The results of previous studies in combination with those of the current experiment suggest that high-fat diets may increase fatty acid oxidation and spare glucose in situations of high energy demand. However, this alteration in energy substrate use may not be sufficient to substantially affect blood acid–base balance during a short period of high-intensity exercise.
Posthandling levels of blood lactate were 7.5% higher (P < 0.05) in pigs fed the fat-supplemented diet (Table 5). However, given the large changes in blood lactate concentrations associated with short-term, acute handling (Hamilton et al., 2004), this magnitude of change is relatively small. The higher lactate concentration in pigs fed the fat-supplemented diet can be partially attributed to the numerical difference in the baseline lactate level, because the increase in blood lactate during handling was similar for the 0 and 5% fat-supplemented treatments (Table 4). Fat supplementation did not affect the posthandling values of HCO3–, base excess, and pH, or the changes in these variables during handling (Table 4). These results differ from those of Greenhaff et al. (1988), who reported a lower blood lactate, HCO3–, and pH in the resting state and after exercise in humans fed a high-fat, low-carbohydrate diet compared with individuals fed a low-fat, high-carbohydrate diet. Therefore, the results of the current study suggest that adding 5% supplementary fat to the diet for 3 wk had little effect on blood acid–base balance in pigs subjected to a short-term, acute handling model.
Effect of Handling
The effect of handling can be evaluated by comparisons of the measurements taken before and after the handling test within the same treatment. Blood pH, HCO3–, base excess, and TCO2 were decreased (P < 0.01), whereas lactate, PO2, glucose, and rectal temperature were increased (P < 0.01) in all treatments during handling (Tables 3 and 5). However, there was no effect of handling on PCO2 and ß-hydroxybutyrate concentrations (Tables 3 and 5). The effects of handling on FFA and O2S levels varied with treatment. Handling increased FFA and O2S levels in pigs fed 150 but not 0 ppm L-carnitine (Table 3). Free fatty acids were increased (P < 0.05) during handling in pigs fed both 0 and 5% added fat; however, O2S levels increased (P < 0.05) only in animals fed the 5% added fat diet (Table 5).
Blood levels of PO2 and O2S are indicators of the amount of oxygen available to the tissues. In the current study, the increase in blood PO2 during handling in all treatments and in O2S in pigs fed 150 ppm L-carnitine or 5% fat suggests that oxygen supply was probably not a limiting factor to aerobic metabolism, unless the capacity of the muscle tissue to extract oxygen from blood was decreased. Physical exercise and/or electrical stimulation may trigger catecholamine release by the adrenal medulla, causing alterations in the functioning of the cardiovascular system and changes in metabolism (Bhagavan, 1992), which trigger responses in blood metabolites and gases that result in alterations of the acid–base balance. These alterations are proportional to the intensity and duration of the stressful stimulus and normally result in a substantial decline in blood pH (Bertol et al., 2002; Hamilton et al., 2004 Hamilton et al., 2002). This change was observed after handling in the current study, as indicated by the increase in blood lactate and concomitant decrease in blood pH, HCO3–, and base excess in all treatments. These results are in agreement with the alterations observed in pigs submitted to varying degrees of stress caused by physical exercise, restraint, and/or electric stimulation (van den Hende et al., 1970; Bertol et al., 2002; Hamilton et al., 2004 Hamilton et al., 2002). Elevated concentrations of organic acids in the blood, such as lactic acid, and decreases in blood HCO3–, which is the main extracellular buffer, are responses characteristic of metabolic acidosis as described by Bhagavan (1992). The increases in blood glucose concentrations during handling observed in the current study are in agreement with previous research in pigs after exercise (van den Hende et al., 1970), after shipping stress (Hicks et al., 1998), and after acute immobilization stress (Rosochacki et al., 2000). Again, these changes and the increase in circulating free fatty acids caused by handling are stimulated by epinephrine release, as described by Bhagavan (1992). Catecholamines have been shown to stimulate glycogenolysis in muscles and liver, gluconeogenesis in the liver, and lipolysis in adipose tissue, and to suppress insulin, resulting in an increase of circulating glucose and FFA. During intense exercise, anaerobic metabolism becomes essential to supply the energy demand for muscle activity, which results in rapid glycogen degradation, increased glucose uptake, and increased lactate release by the muscle (Hocquette et al., 1998).
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Implications
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Feeding finishing pigs 150 ppm of L-carnitine and/or 5% fat for 3 wk had limited effects on handling-induced changes in blood acid–base equilibrium balance. Additional research is needed to clarify the effects of different levels and times of feeding of L-carnitine and/or fat during periods of longer-term handling.
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Footnotes
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1 The present research was carried out with the support of CNPq, a Brazilian governmental institution dedicated to the scientific and technological development. 
3 Current address: Genetipork USA, P.O. Box 425, Petersburg, IL 62675.
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 February 26, 2004.
Accepted for publication August 13, 2004.
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Abstract
Introduction
