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Unidad de Nutrición Animal, Estación Experimental del Zaidín (CSIC), 18100 Armilla, Granada, Spain
4To whom correspondence should be addressed. E-mail: rosa.nieto{at}eez.csic.es.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • protein synthesis • muscle • viscera • Iberian pigs • lysine deficiency
Extensive systems to produce heavy pigs are located in some areas of the Mediterranean basin (Southwest of Spain, South of Portugal, Corsica). They rely on local breeds (Iberian, Corsican) and on a rather unstable availability of natural resources. The pigs are slaughtered at 140–160 kg body weight (BW)5 and 18–24 mo of age. The low productivity of these rearing systems explains current tendencies to shorten their productive cycles, which is accomplished by intensification of management during the pig’s growing period. Iberian piglets are fed to achieve a growth rate that allows a final fattening period in the Mediterranean forest on acorn and pasture, a requirement of utmost importance for the production of high-quality dry-cured meats.
Studies with growing Iberian pigs (15–50 kg BW) in our laboratory, demonstrated their low genetic potential for lean tissue deposition (1). The maximum deposition of protein (mean of 74.0 g/d) was achieved with a diet supplying 129 g crude protein (CP) (with an amino acid composition balanced according to the ideal protein concept; 2,3) per kg dry matter (DM) [6.86 g digestible ideal protein/MJ metabolizable energy (ME)], fed at levels close to ad libitum consumption. Increasing the level of protein did not increase protein accretion. The factors that limit protein deposition in Iberian pigs remain unknown. In a direct comparison between genotypes, carried out at 
28 kg BW, we observed that whole-body protein synthesis and degradation were lower in Iberian than in Landrace pigs when given an optimal dietary amino acid supply to express their genetic potential for lean tissue deposition [5.84 vs. 8.00 and 4.71 vs. 6.47 g N/(kg0.75 · d), respectively; 4]. However, the protein synthesis/protein accretion ratios did not differ (5.17 vs. 5.33, respectively). Differences in proportional weight of viscera and in carcass composition between obese and lean pigs are well recognized (5–7) and may explain in part the unequal efficiencies of growth or specificity of response to exogenous manipulation of protein metabolism. As a result of the different metabolic rates and protein synthetic capacities between visceral and nonvisceral tissues, measurements of protein turnover at the whole-body level may not provide enough information on dissimilar protein synthesis rates between pig genotypes.
This study was designed to investigate possible differences in protein synthesis rate, in specific tissues, between Iberian and Landrace pigs, the latter chosen as a model genotype with a high genetic potential for lean growth. This information will presumably help to understand protein synthetic or degradative responses to changes in nutrient supply at the tissue level. The tissues chosen for this study were skeletal muscle, liver, and duodenum, the first because it is the main protein reservoir and because of its importance in production processes, the other 2, for their highly active metabolic rate, and protein turnover, which can influence the availability of nutrients to peripheral tissues. Additionally, we also observed that whole-body protein turnover in Iberian pigs was less sensitive to a lysine-deficient supply than in Landrace pigs (4). This nutritional situation is common for Iberian pigs during the final fattening stage, which takes place outdoors and suggests the development of adaptive mechanisms to lysine shortage. With this background, in the present study, differences in protein synthetic rates in tissues were investigated in Iberian and Landrace pigs fed adequate protein and amino acid diets (A; approaching maximum protein deposition in each genotype) or lysine-deficient (DLys) diets, using the flooding dose method (8) with [2H5]-phenylalanine as the tracer.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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2 mo old (55–60 d for Ib and 65–70 d for Ld pigs) supplied by Sánchez Romero Carvajal Jabugo and "Granja el Arenal," respectively. Three diets were fed to pigs of each breed: 2 adequate amino acid composition diets containing 120 (A12) or 160 (A16) g crude protein (CP)/kg diet as fed, and 1 diet providing 35% (37 and 33% for Ib and Ld pigs, respectively) of the recommended lysine intake according to the ideal protein concept (2,3), all based on wheat and corn gluten meal (Table 1). The DLys diets were given at 120 g CP/kg for Ib and 160 g CP/kg for Ld pigs. The balanced diets were obtained by supplementation with L-lysine in amounts to attain the same concentration of this amino acid per unit of dietary protein, and specifically, that stated for the ideal protein [70 g/kg protein (2)] to achieve an optimum amino acid balance for growth. The concentrations of CP of the experimental diets were fixed to match the unequal potential for protein deposition of the Ib breed [see Nieto et al. (1)] and conventional pig genotypes. The DLys diets were formulated at the level of dietary protein considered more adequate for each breed. In this way, lysine deficiency was tested in each breed under its otherwise optimal dietary protein:energy ratio. All diets were approximately isoenergetic and supplied 13.3–13.9 kJ ME/g dry matter. Within each breed, the contrasts made were as follows: 1) adequate diets differing in their protein level (PL; A12 vs. A16) and 2) adequate vs. inadequate amino acid composition diets (AAP; A vs. DLys).
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19 and 21 kg for Ib and Ld pigs, respectively. Daily food allowance was split into 4 equal portions that were offered every 6 h (1000, 1600, 2200, and 0400 h). Pigs were fed at 90% of ad libitum consumption, calculated as a function of live weight following the linear regression described by Nieto et al. (9) for Ib pigs. After an adaptation period to the corresponding dietary treatment for 3 d, the pigs were surgically implanted with indwelling catheters in each of the exterior jugular veins. The catheters were fabricated from PVC tubing (1 mm i.d. x 1.5 mm o.d., Rüschelit®, Rüsch Medica España) 1 m in length. Surgery was carried out under sterile conditions in a properly equipped operating room. After surgery, the pigs were placed in mobile cages (1.0 x 1.8 m) at 21 ± 1°C under rigorous antiseptic conditions. Once recovered, the pigs remained in the conditions previously described for 8 d. After this period, they were infused for 10 min by means of a peristaltic pump with a flooding dose of phenylalanine (5–10 times the pig’s free phenylalanine pool of which 15% was [2H5]-phenylalanine) to determine fractional protein synthesis rate (FSR) in tissues. The mean amount of phenylalanine infused per pig was 2.89 g prepared in sterilized saline (the exact amount was adjusted according to individual body weights). A blood sample was taken from each pig 10 min before starting the infusion to determine the natural enrichment of phenylalanine; a series of blood samples were taken at 12, 15, 20, 25, 30, and 40 min after the start of the infusion to define the enrichment curve of the free phenylalanine pool in plasma and tissues. After that, the gilts were slaughtered by injection of a lethal dose of sodium thiopental (Sodium Pentothal®, Abbott Laboratories) and samples of tissues (2–3 g) were taken and immediately placed in liquid nitrogen until their subsequent analysis. The tissues and organs sampled for FSR determination were the muscles longissimus dorsi (ld), biceps femoris (bf), and semimembranosus (sm), from the left half of the animal, the liver, and the duodenum (50 cm distal to the pyloric sphincter). After completion of tissue and organ sampling, the same 3 muscles from the right half of the animal, the liver, and other components of the gastrointestinal tract (GIT; stomach, rest of the small intestine and large intestine) were dissected and weighed. The experimental protocol was approved by the Bioethical Committee of Consejo Superior de Investigaciones Científicas (CSIC), Spain. Analytical procedures. All analyses were performed in duplicate. Dry matter content of feed was determined by standard procedures (10) and gross energy contents of feed and total nitrogen in diets and freeze-dried tissues were analyzed as described by Nieto et al. (1). RNA in tissues was estimated following the procedure described by Fleck and Begg (11).
Isotopic enrichment determination. Plasma was prepared by centrifugation of blood at 1000 x g for 15 min at 4°C and stored at –20°C for further analysis. A plasma aliquot was deproteinized with sulfosalicylic acid (SSA) to a final concentration of 80 g/L, desalted on AG50W-X8 resin (H+ form, 100–200 mesh, Sigma Chemical) with 2 mol/L NH4OH, and freeze-dried. Frozen tissue samples were powdered in a freeze mill (Spex 6700, Glen Creston) and an aliquot of 0.5 g homogenized with 3.6 mL of SSA (80 g/L) and centrifuged at 2000 x g for 15 min. The supernatant was desalted as described for plasma; the protein pellet was washed 3 times with 3 mL of 70 g/L SSA and centrifuged; 0.1 g of the pellet was dissolved in 0.3 mol/L NaOH and hydrolyzed with 7 mL of HCl 4 mol/L for 18 h at 110°C, evaporated to dryness and resuspended in 0.5 mol/L sodium citrate, pH 6.3. Plasma and tissue phenylalanine preparations were derivatized to obtain the tributyldimethylsilyl (TBDMS) derivatives (12) and analyzed by GC-MS in the electron impact mode (Finnigan Masslab). The ions at m/z 336 and 341 were monitored for the TBDMS derivatives of free phenylalanine in plasma and tissue homogenates. For the protein-bound phenylalanine, the enzymatic conversion to ß-phenylethylamine (13) was performed before derivatization and the fragment ions at m/z 180 and 183 were monitored for the TBDMS derivatives.
Calculations and statistics.
The method employed for the determination of protein synthesis in rates tissues was the "flooding" dose technique developed by Garlick et al. (8). Fractional protein synthesis rates in tissues (FSR; %/d) were calculated from the following equation (8):
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were Sb is the isotopic enrichment of the phenylalanine bound to tissue protein once the enrichment at t = 0 (natural abundance, assumed to be the same as in plasma protein) has been subtracted; Sa is the area under the curve drawn by the isotopic enrichment of the free phenylalanine pool, from t = 0 until the end of the sampling period, calculated by trapezium-based analysis for each pig and tissue; and t is the labeling time in days.
Absolute rate of protein synthesis (ASR, g/d) in each muscle or viscera was calculated according to the equation:
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The capacity for protein synthesis (CS) in the ld and bf muscles was calculated according to the equation:
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and the translational efficiency (kRNA) in the same muscles following the equation:
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All statistical analyses were carried out by means of a computer software package (SAS Institute). The experimental data were subjected to two 2-way ANOVA, the first with dietary protein level [(PL): 120 (A12) vs. 160 (A16) g CP/kg] and breed (Ib vs. Ld) as main effects. In the second, the main effects were amino acid composition (AAP: A or DLys) and breed (Ib vs. Ld). The data presented in Tables 2, 3, 4, 5, 6, 7 correspond to the mean for each of the 4 treatment combinations ± SEM. When interactions between the 2 main factors were significant, the means for each of the 4 treatment combinations were compared by one-way ANOVA, and the statistical differences (P < 0.05) were determined by Tukey’s t test. Differences were considered significant at P < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Effects of breed and dietary protein level
No major incidents were registered during the experiment. DM intake of pigs fed diets with a balanced amino acid composition was 104.0 ± 1.07 g/(kg BW0.75 · d), with no differences between breeds or dietary protein intakes (Table 2). Weight gain (g/d) was greater in Ld pigs (P < 0.001) and tended to increase with the higher protein intake (P = 0.057); this was more apparent for Ld pigs. Similar effects were observed when growth rates were expressed relative to final BW (Table 2).
The weight of muscles and viscera was strongly influenced by the breed but not by the protein content of the diet. The muscles studied weighed, in absolute terms (g), between 32 and 48% less in Ib than in Ld pigs. However, the Ib gilts had significantly smaller body weights (10%; P < 0.001) at the start of the experiment, along with slower growth rates (P < 0.001). For these reasons, comparisons of size of muscle and viscera between breeds were performed on the basis of BW (Table 2). This analysis showed that Ld pigs had larger muscles in all cases (P < 0.001 for bf and sm; P < 0.01 for ld). In the Ib breed the ld, bf, and sm muscles contributed 20, 32, and 31% less, respectively, to total BW.
The small intestine relative weight was 33.5 and 31.4 g/kg BW in Ib and Ld pigs, respectively, with no difference between breeds. The remaining viscera studied contributed more to the total BW in Ib than in Ld gilts. The relative weights of the liver, stomach, and large intestine were 18, 38, and 39% greater, respectively, in the Ib gilts (P < 0.001). Correspondingly, the complete GIT (obtained by adding the weights of stomach, small and large intestine) had a relative weight that was 21% higher for Ib pigs (P < 0.001).
Protein synthesis in muscle. The fractional rates of protein synthesis in muscular tissues differed between genotypes (Table 3). The FSRs were 25, 31 and 22% greater in the ld (P < 0.01), bf (P < 0.001), and sm (P < 0.01) muscles, respectively, in Iberian pigs compared with Landrace pigs. Surprisingly, the concentration of dietary protein did not affect muscle FSR. The FSR in each muscle was 7.89 ± 0.336 vs. 6.33 ± 0.285%/d for ld, 8.28 ± 0.361 vs. 6.29 ± 0.210%/d for bf and 7.74 ± 0.231 vs. 6.37 ± 0.359%/d for the sm in the Ib and Ld gilts, respectively. No significant interactions between breed and dietary protein level were detected.
Despite their smaller FSR, absolute protein synthesis rates (ASR) were higher in Ld than in the Ib gilts because of the larger muscles in the former (P < 0.001 to 0.05, Table 3). The protein level of the diet had no effect on ASR. The ASRs (g/d) obtained for the same muscles listed above were: 8.86 ± 0.534 vs. 10.72 ± 0.676; 3.25 ± 0.203 vs. 4.50 ± 0.247, and 3.79 ± 0.163 vs. 5.58 ± 0.491 for Ib and Ld gilts, respectively.
Neither the capacity for synthesis of tissue protein (CS) nor the translational efficiency (kRNA) in ld and bf muscles were affected by breed or dietary protein level with the exception of CS in the bf muscle, which was 21% greater for the Ib breed (P < 0.05) (Table 3).
Protein synthesis in viscera. FSRs in liver and duodenum did not differ between the breeds (Table 4). The concentration of dietary protein also had no effect. The tissue FSRs in pigs of the Ib and Ld breeds were 46.8 ± 1.48 and 43.9 ± 1.31%/d for liver and 64.3 ± 3.39 and 66.2 ± 3.01%/d for duodenum, respectively.
Liver ASR (g/d) was affected by both breed and level of dietary protein (P < 0.05). The daily amount of protein synthesized in the liver was higher in Ib than in Ld gilts. In both breeds, more protein was synthesized in the liver when pigs were fed the higher protein diet (Table 4). The ASR in the small intestine, calculated using duodenum FSR, was not influenced by breed or dietary protein content.
Effect of lysine deficiency
Feed intake [g DM/(kg BW0.75 · d)] was lower in pigs fed DLys diets than in those fed diets with adequate amino acid content (5.4 and 14.3% for Ib and Ld pigs, respectively, P < 0.05, Table 5). Weight gain was severely reduced in both pig breeds (50%, P < 0.001) when DLys diets were fed.
Muscle weights were affected by the amino acid deficiency (P < 0.001–P < 0.05, Table 5), particularly in the Ld gilts. All of the muscles had significantly lower absolute weights, and ld was more affected than the other 2 muscles studied. In the Ld breed, the reductions in size were 34, 19.3, and 19.8% for ld, bf, and sm muscles, respectively; in Ib pigs, the weights of the bf and sm muscles were slightly reduced (5.0 and 6.6%, respectively) and the ld decreased 22% compared with pigs fed the adequate amino acid composition diet.
In examining the size of the viscera (Table 5), only the liver and stomach absolute weights were not affected by DLys treatments. In the Ib breed, the greatest reduction in size was in the large intestine (<26.5%); in Ld gilts, the small intestine was the most affected viscera (<18.3%). The size of the whole GIT also decreased in both breeds (P < 0.01).
Protein synthesis in muscle. The deficient lysine supply decreased both FSR and ASR in all of the muscles examined in both porcine breeds (P < 0.001, Table 6). Mean FSR reductions were 46 and 49% for Ib and Ld gilts, respectively. Comparatively higher reductions in ASR values were detected for Ld pigs (Breed x AAP interactions were significant for all of the muscles considered, P < 0.01–P < 0.05). Lysine deficiency decreased CS in the 2 muscles analyzed from both breeds (P < 0.05); however, this effect was more marked on kRNA (P < 0.001) because this parameter was reduced in both breeds up to 33–39% in the 2 muscles studied.
Protein synthesis in viscera. Significant interactions (P < 0.05) between breed and amino acid composition were observed for FSR and ASR values due to dissimilar effects of lysine deficiency in the visceral tissues of the 2 breeds (Table 7). In Ib gilts, for liver and duodenum (or small intestine in the case of ASR), both FSR and ASR remained similar or tended to increase. In Ld pigs, these parameters tended to be reduced (P = 0.07–0.17) and in the case of liver ASR, the reduction was significant (P < 0.05).
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The flooding dose technique used focused on muscle tissue, which has a relatively slow protein turnover rate. On the contrary, liver and duodenum have high rates of protein turnover. The plasma free phenylalanine enrichment curve (see Fig. 1 as an example) showed that the flooding of the free amino acid pool was adequate and that these conditions were maintained for the muscle free pool. For the viscera, the enrichment declined 0.65 and 0.60 of plasma values for liver and duodenum, respectively, as a result of the dilution by free amino acid coming from the degraded protein. This fact, together with the production of export proteins (in the case of the liver), would lead to an underestimation of protein synthesis rates in these visceral tissues
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The values for FSR obtained in muscle tissues in the present study were similar to those observed by other authors in pigs of similar weights (Table 8). Surprisingly, FSRs in Ib pig muscles were higher than those of the conventional breed. Ld pigs synthesized daily a smaller proportion of their muscular protein (%/d) but had a greater protein pool than Iberians, resulting in a higher absolute protein synthesis (g/d). The greater proportion of muscular protein synthesized each day in the Ib breed, averaging between 20 and 25% higher for the 3 muscles analyzed, did not result, however, in larger muscles. The synthetic capacity and translational efficiency in muscle were not significantly different between genotypes (except for the CS in the bf); thus, these parameters do not provide information relevant to an explanation of FSR differences between breeds. On the other hand, the CS values surpassed the majority of those found in the literature, whereas those of kRNA were smaller. Davis et al. (15) observed values similar to ours in 26-d-old pigs, in which values are more likely to be still greater, at least for the efficiency of translation. Their estimates ranged between 9.3 and 15.0 for CS and 7.5 and 7.2 for kRNA.
The greater FSR of muscle protein observed in Ib pigs may be related to the type of muscle fiber. Type I muscle fibers (predominantly oxidative) were reported to be of greater abundance and diameter in Ib than in the Ld pigs for the longissimus lumborum muscle (16). Other authors made muscle fiber type comparisons between different breeds and also observed that unimproved and wild breeds have a higher capacity for oxidative metabolism than improved ones (17). In the studies of Baillie and Garlick (18) and Garlick et al. (19), these types of fibers showed FSR greater than those of type II muscle fiber, whose metabolism is predominantly glycolytic. In more recent studies, Lobley et al. (20) reported higher FSR (11.5–13.8% higher) in mixed muscle proteins from pure Aberdeen Angus compared with Charolais steers, with the former having slower growth rates, smaller lean tissue proportions, and higher type I (slow oxidative) fiber frequency and area in the muscles studied (21).
But, if the Ib pig has higher muscle FSR, why are their muscles smaller? The smaller muscular protein pool is likely to be associated with increased rates of muscle protein degradation. If we assume that the muscles and muscle protein grow in a manner similar to the whole animal (Table 2), a mean value for fractional protein growth of 1.93 and 2.39%/d in Ib and Ld pigs, respectively, is obtained. When this mean value is subtracted from the corresponding mean FSR value in muscle, 7.97 and 6.33%/d for each breed (Table 3), fractional protein degradation rates (FDR) of 6.04 and 3.94%/d for Ib and Ld pigs, respectively, are obtained. These figures indicate that FDR in Ib pigs is >50% higher than in the Ld genotype, and also that >75% of the protein synthesized in muscle is subsequently degraded. In the Ld breed, however, the breakdown of muscular protein would represent 62% of the daily synthesized protein. The high muscle protein turnover (higher rates of synthesis and degradation) estimated for Ib pigs might explain the low partial efficiency of metabolizable energy for protein deposition found in this native breed (1).
FSR in muscle was not affected by the concentration of dietary protein during the experimental period in either breed. However, in other studies, an increase in plasma free amino acid concentration was a strong stimulus for protein turnover in muscle, increasing both protein synthesis and degradation. Watt et al. (22) observed in pigs of 25 kg live weight that an infusion of amino acids per se brought about an increase in the incorporation of amino acids into muscular protein independently of insulin levels, which remained constant during the trial. Sève et al. (23) also demonstrated an increase in FSR in weanling piglets in conjunction with an elevation in translational efficiency, when the concentration of dietary protein was augmented from 15 to 30%. Sève et al. (24) observed an increase in FSR when the quantity of protein ingested was elevated in isoenergetic diets. However, the change in the concentration of dietary protein in these last-mentioned trials (124–203 g of CP/kg of diet) was considerably greater than that employed in the present study.
Lysine deficiency. The classical hypothesis on the regulation of muscle mass and its response to some type of amino acid deficiency is that such regulation is accomplished by means of changes in FSR (25). Our results appear to corroborate this hypothesis. We found that the severe lysine deficiency applied brought about a dramatic decrease in FSR in both breeds (Table 6). Wei Wei (26) also found a considerable decrease in the FSR values of the bf and abductor muscles in 20-kg pigs offered diets with a severe deficiency in isoleucine, histidine, or tryptophan. Cortamira et al. (27) observed as well that a tryptophan deficiency decreased the synthesis of protein in the ld and sm muscles of 24-d-old suckling pigs. The effect of amino acid deficiencies on the process of RNA translation was explained as a disintegration of the polysomes forming oligosomes, which are not able to initiate the translation process (28). Then, translational efficiency and, therefore, synthesis rates would be affected as was observed in the present work.
Visceral protein metabolism
Despite the methodological considerations mentioned earlier, our results provide a reasonably accurate comparative estimation between breeds and indicate that the contribution of protein turnover and its associated energetic cost in visceral tissues to that of the whole body is disproportionate to their contribution to total body protein. Our results are within the range of values for FSR in visceral tissues published by other authors (Table 8). This wide range is due to both age and methodological differences in the experiments reported. Therefore, although the FSR reported in the present work for these tissues should be taken with caution, they point out their importance in terms of whole-body protein (and energy) metabolism and stress the significance of these processes in an unimproved breed such as the Ib with high relative proportions of visceral tissues.
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In the present work, none of the parameters studied concerning the small intestine were affected by the level of dietary protein. Lobley et al. (29) found no significant effect of the protein level on FSR in this tissue, although a tendency to increase when increasing the level of intake was noticed. Davis et al. (30) indicated that the small intestine of neonatal pigs did not respond to amino acid infusions. Sève et al. (23) observed in weanling pigs (17 d old) that increasing protein intake augmented deposition of protein in the duodenum, whereas protein synthesis tended to diminish, thereby associating the increase in protein deposition with a concomitant decrease in the FDR. In later trials carried out in heavier pigs (24), no changes in FSR in the duodenum were found when the quantity of dietary protein was increased.
Lysine deficiency.
FSR in liver and duodenum seemed to be differently affected by the lysine deficiency in each breed (Table 7). In this situation, liver FSR tended to increase in Ib pigs, whereas in the Ld breed, the opposite trend was observed. Other authors (27,31) also observed a decrease in liver FSR in Large White piglets (1 mo old) fed a diet deficient in tryptophan. Wei Wei (26) observed a decrease in liver FSR in 20-kg pigs of the same breed when fed an amino acid–deficient diet (isoleucine, histidine, or tryptophan deficiency).
In the case of duodenum, a situation similar to that of the liver was found. Small intestine size was slightly reduced in Ib pigs fed DLys diets, whereas in Ld pigs, this dietary treatment provoked a marked decrease in organ size. If it is assumed that FSR for the whole small intestine is similar to that for the duodenum, this organ reduction would result from a considerable decrease in the FSR. Nevertheless, the observed effects of lysine deficiency on the visceral organs were rather moderate in relation to those found in muscle. In this sense, as pointed out by Ponter et al. (31), a possible protective mechanism may exist for maintaining the functional activity of this tissue when nutritional conditions are less than optimal, under either conditions of fasting or deficient amino acid supply. Nevertheless, both liver and small intestine appear more sensitive to an amino acid deficiency in dietary protein than to alterations in protein quantity.
The contributions of liver and GIT to total BW highlighted important differences between breeds, and were substantially higher in the Ib pigs. This fact might have also consequences in energetic terms. If the high rate of muscle protein turnover is considered along with the higher viscera size, our findings help to explain the low efficiency for protein and energy utilization observed in this native breed in comparison with conventional pig breeds (1).
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Supported by Spanish CICYT grant No. 1FD97–0432. M.G.R. was recipient of a Marie Curie Training Site fellowship to perform the mass spectrometry work at the Rowett Research Institute.
3 Supplemental Tables 1 and 2 are available with the online posting of this paper at www.nutrition.org.
5 Abbreviations used: A, adequate amino acid diet; A12, adequate amino acid composition diet with 120 g crude protein/kg; A16, adequate amino acid composition diet with 160 g crude protein/kg; AAP, amino acid composition; ASR, absolute protein synthesis rate; bf, biceps femoris; BW, body weight; CP, crude protein; Cs, capacity for protein synthesis; DLys, lysine-deficient diet; DM, dry matter; FBW, final body weight; FDR, fractional protein degradation rate; FSR, fractional protein synthesis rate; GIT, gastrointestinal tract; Ib, Iberian; kRNA, translational efficiency; Ld, Landrace; ld, longissimus dorsi; ME, metabolizable energy; MPE, molar percent excess; PL, protein level; Sa, isotopic enrichment of the free phenylalanine pool; Sb, isotopic enrichment of phenylalanine bound to tissue protein; sm, semimembranosus; SSA, sulfosalicylic acid; TBDMS, tributyldimethylsilyl.
Manuscript received 15 June 2004. Initial review completed 13 August 2004. Revision accepted 19 November 2004.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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