Sensory quality of pork is a complex phenotype determined by interactions between genetic and environmental factors. This study aimed at describing the respective influences of breed and production system on the development of pork quality. Plasma stress indicators and Longissimus muscle (LM) composition, physicochemical and sensory quality traits were determined in two contrasted breeds - the conventional Large White (LW, n=40) and the French local Basque (B, n=60). Pigs were reared in either a conventional (C; n=20 per breed), alternative (A; sawdust bedding and outdoor area, n=20 per breed) or extensive system (E; free-range, n=20 B). All the pigs from A and C systems were slaughtered at the same slaughterhouse, whereas B pigs from the E system were slaughtered at a local commercial abattoir. Major breed differences were found for almost all traits under study. LM from B pigs exhibited higher lipid, lower water and collagen concentrations, as well as lower collagen thermal solubility (P0.05) influence plasma stress indicators, LM chemical composition and physicochemical or sensory traits of pork. In contrast, within the B pigs, the E system affected the meat quality more. Lower plasma cortisol levels (P<0.05), but higher plasma lactate, creatine kinase and lactate dehydrogenase activities, and more skin lesions (P<0.05), indicating higher muscular activity during pre-slaughter handling, were found in pigs produced in the E compared with the C system. E pigs exhibited higher meat pH1 and pHu values and shear force (P<0.01) and exhibited lower lightness, hue angle and drip and thawing losses (P<0.01) compared with the C pigs, whereas LM lipid, protein or collagen concentrations were not affected. Regarding sensory traits, the E system produced redder meat, but did not impact the eating quality of pork. Altogether, this study demonstrates that differences in meat quality between B and LW breeds can be modulated by extensive pig production system.

Cold environment represents an external stress modulating animal growth and energy use. At muscle level, adaptation to cold conditions potentially involves energy homeostasis regulation gauged by the adenosine monophosphate (AMP)-activated protein kinase (AMPK). Our study aimed at evaluating the bare effects of short- and long-term cold exposure on growth performance, carcass traits, and metabolic characteristics of the oxidative semispinalis (SS) muscle and glycolytic LM and to evaluate the reversibility of short-term effects, with a special emphasis on AMPK activity. A total of 84 pigs fed ad libitum and individually housed were submitted after weaning to either Cold (from 23 ± 1 to 15 ± 3°C) or thermoneutral (T; from 28 ± 1 to 23 ± 1°C) temperature up to 24.7 ± 1.6 kg BW (25 BW). Twelve Cold and 12 T piglets were then slaughtered the same day. Eighteen remaining Cold piglets were reared at 12 ± 2°C (CC) whereas 18 Cold and 24 T piglets were reared at 23 ± 4°C (CT and TT, respectively) and slaughtered at 114.3 ± 5.9 kg (115 BW). The LM and SS samples were analyzed to determine glycolytic potential (GP), activities of lactate dehydrogenase (LDH), citrate synthase (CS), and β-hydroxy-acyl-CoA dehydrogenase (HAD) and to quantify AMPK phosphorylation Threonine 172 phosphorylated form of AMPK α1+α2 isoforms (pAMPK) / total AMPK α1+α2 isoforms (AMPK). Despite a greater ADFI (P < 0.001), Cold piglets exhibited less ADG (P < 0.001) and body fatness (P < 0.03) attesting an acute adaptation to a short-term cold exposure. A long-term cold adaptation evaluated on 115 BW pigs increased ADFI (P < 0.001) but did not influence ADG and carcass lean meat content. Cold environment influenced the dynamic of muscle metabolism in a muscle type dependent manner corresponding to an earlier and acute adaptation in SS from 8 kg onward and a belated adaptation in LM from 25 BW to 115 BW. Cold exposure was associated with a progressive increase of muscle oxidative capacity, first in the SS with greater HAD (P = 0.002) and CS activities (P = 0.03) at 25 BW and then both in SS and LM at 115 BW (P < 0.001). Conversely, in LM of CC pigs, increased GP (P < 0.001) and LDH activity (P = 0.03) were observed in addition to increased CS and HAD activities, highlighting the ability of LM to increase both its glycolytic and oxidative metabolism and to diversify its energy substrates. Pigs from CC group exhibited also less pAMPK/AMPK (P < 0.01) specifically in red SS muscle, denoting a reduced metabolic stress of this muscle after a long-term cold adaptation.

Selection to decrease Residual Feed Intake (RFI) is a relevant way to improve feed efficiency in growing pigs. However, RFI criterion is correlated with body composition and muscle characteristics. Present study evaluated adaptive responses to divergent selection on RFI on muscle metabolism and homeostasis through AMP-activated protein kinase pathway. Consequences on technological and sensory meat quality were also analyzed in two lines of Large White pigs after six generations of divergent selection on RFI.RFI- pigs (n=60) exhibited similar growth rate but lower feed intake and conversion ratio, and were leaner than RFI+ pigs (n=57). Despite higher glycogen content, metabolic enzyme capacities involved in glycolytic, fatty acid oxidation pathway and energy balance were reduced in the Longissimus muscle of the RFI- pigs. Reduced muscle homeostasis in the RFI- line influenced post-mortem metabolism and impaired technological quality traits of loin and ham but had only slight effects on meat eating quality. (C) 2012 Elsevier Ltd. All rights reserved.

Residual feed intake (RFI) is defined as the difference between the observed feed intake and that expected based on requirements for maintenance and production. A divergent selection was conducted during 4 generations in Large White male pigs to produce low and high RFI lines. The present study aims at determining the influence of this selection on biochemical and histological traits of skeletal muscle, and relating these changes to correlated effects on growth, carcass composition, and meat quality traits. At 8 d preslaughter, biopsies from the LM were taken in the fed state on 14 females from each RFI line fed ad libitum. Animals were slaughtered at 107.8 ± 8.0 kg of BW without any previous fasting. Samples of LM, semimembranosus (SM), biceps femoris (BFM), and rhomboideus muscles were taken at both 30 min and 24 h postmortem. Myofiber typing was only assessed in LM. Low RFI pigs ("efficient") had leaner carcasses with greater muscle content (P < 0.001), less backfat thickness (P < 0.001), and less intramuscular fat content in all 4 muscles (P < 0.01 to P = 0.04). Their greater muscle content was associated with hypertrophy of all fast-twitch fibers. Glycogen content in all glycolytic muscles (i.e., LM, SM and BFM), was greater in low than high RFI pigs. The greater accumulation of glycogen in LM of low RFI pigs was specifically located in the fast-twitch glycolytic IIBW fibers, which correspond to fibers containing IIb, IIb + IIx, or IIx myosin heavy chains. The difference in muscle glycogen content between RFI line pigs was more significant in the living animals (P = 0.0003) than at 30 min postmortem (P = 0.08). This was associated with a decreased ultimate pH (P = 0.001), and greater lightness of color (P = 0.002) and drip loss (P = 0.04) in LM of low than high RFI line pigs, suggesting that selection for reduced RFI may impair some meat quality traits, such as water-holding capacity. Pigs from the low RFI line exhibited a greater (P = 0.02) percentage of IIBW fibers in LM and tended (P < 0.10) to have less lipid β-oxidative capacity in LM, SM, and BFM. In contrast, no difference (P > 0.10) between lines was found for citrate synthase and lactate dehydrogenase activities, mitochondrial activity, and expression of genes coding for uncoupling proteins 2 and 3. Differences between RFI pigs in plasma leptin, cortisol, and thyroid hormone concentrations are presented and discussed. In conclusion, selection for low RFI influenced muscle properties in a way favoring muscle mass, but likely impairing meat quality.

Mitochondrial respiration rates and their regulation by ADP, AMP and creatine, were studied at different free Ca2+ concentrations (0.1 versus 0.4 μm) on permeabilized fibre bundles of rabbit skeletal muscles differing in their myosin heavy chain profiles. Four fibre bundle types were obtained: pure types I and IIx, and mixed types IIax (approximately 50% IIa and 50% IIx fibres) and IIb+ (60% IIb fibres, plus IIx and IIa). At rest, pure type I fibres displayed a much higher apparent Km for ADP (212 μm) than IIx fibres (8 μm). Within the IIax and IIb+ mixed fibre bundle types, two KADPm values were observed (70 μm and 5 μm). Comparison between pure IIx and mixed types indicates that the intermediate Km of 70 μm most probably corresponds to the mitochondrial affinity for ADP in IIa fibres, the lowest Km for ADP (5 μm) corresponding to IIx and IIb types. Activation of mitochondrial creatine and adenylate kinase reactions stimulated mitochondrial respiration only in type I and IIax fibre bundles, indicating an efficient coupling between both kinases and ADP rephosphorylation in type I and, likely, IIa fibres, since no effect was observed in pure IIx fibres. Following Ca2+‐induced activation of myosin‐ATPase, an increase in mitochondrial sensitivity to ADP of 45% and 250% was observed in type IIax and I bundles, respectively, an effect mostly prevented by addition of vanadate, an inhibitor of myosin‐ATPase. Ca2+‐induced activation of myosin‐ATPase also prevented the stimulation of respiration rates by creatine and AMP in I and IIax bundles. In addition to differential regulation of mitochondrial respiration and energy transfer systems at rest in I and IIa versus IIx and IIb muscle fibres, our results indicate a regulation of phosphotransfer systems by Ca2+ via the stimulation of myosin‐ATPases in type I and IIa fibres of rabbit muscles.

Four major sarcomeric myosin heavy chains (MyHC) (i.e., I, IIa, IIx, and IIb) are expressed in pig skeletal muscle during postnatal development. The objective of the current study was to compare MyHC composition at mRNA and protein levels in LM, a fast-twitch glycolytic muscle, and rhomboideus (RM), a mixed slow- and fast-twitch oxido-glycolytic muscle, between two pig breeds exhibiting dramatic differences in postnatal muscle growth and meat quality. Eight Large White (LW) and eight Meishan (MS) females were fed under the same standard conditions, and slaughtered at an average BW of 62 kg (131 and 142 d in LW and MS pigs, respectively). In addition to conventional fiber typing by histoenzymology, MyHC composition was analyzed by combining immunocytochemistry, in situ hybridization, and a newly developed real-time PCR assay. Enzyme activities of lactate dehydrogenase, citrate synthase, and beta-hydroxy-acyl-CoA-dehydrogenase were used as markers of glycolytic, oxidative and beta-oxidation capacities, respectively. Results showed that conventional fiber typing in three classes by histoenzymology was insufficient in LM. For the first time, four monoclonal antibodies specific of each MyHC isoform, working in immunocytochemistry, were used. Our results are consistent with the sequential I<-->IIa<-->IIx<-->IIb MyHC transition rule. Breed effect on MyHC composition differed between muscle types. In LM of MS pigs, a shift from IIb to IIx, and to a lesser extent, to IIa, occurred without affecting type I MyHC. In RM, where IIb is absent, a shift from IIx to type I occurred, with a slight decrease in the IIa isoform. Effects were very similar at the mRNA and protein levels, suggesting a transcriptional regulation. In both muscles, MS pigs exhibited a decrease in the relative fiber type specific expression of the fastest isoform (i.e., IIb in LM and IIx in RM). The shift toward a slower phenotype in MS pigs was consistent with a less glycolytic and more oxidative metabolism, potentially using more lipids as fuel. A dramatic increase in cross-sectional area of type I fibers in RM (+27%) and a decrease in that of the fastest IIb fibers in LM (-25%) were observed in MS pigs. Overall, interpretation of earlier data regarding muscle fiber type has been flawed by inaccurate fiber typing in most pig skeletal muscles.

We examined the effects of undernutrition on muscle development during the first postnatal week in pigs. Eighteen piglets were subjected to three nutritional levels (300, 200 or 100 g/(kg body. d) of colostrum then milk) between birth and slaughter at 7 d of age. Longissimus lumborum (LL), a fast-twitch glycolytic muscle, and rhomboideus (RH), a mixed slow- and fast-twitch oxido-glycolytic muscle, were taken for myofiber typing and biochemical analyses. Enzyme activities of lactate dehydrogenase (LDH), citrate synthase (CS) and beta-hydroxy-acyl-CoA-dehydrogenase (HAD) were used as markers of glycolytic, oxidative and lipid beta-oxidation capacities, respectively. Undernutrition selectively decreased (P < 0.001) hypertrophy of the future fast-twitch glycolytic fibers in LL. Contractile and metabolic maturation was delayed in the later maturing LL, as reflected by a decrease in muscle protein concentration (P < 0.01), an increase (P < 0.05) in the percentage of myofibers still expressing the fetal myosin heavy chain (MyHC), a lower postnatal increase in LDH activity (P < 0.001) and a delayed decrease in the percentage of IIa MyHC positive fibers (P < 0.001). Otherwise, restriction tended (P < 0.10) to increase the percentage of slow type I MyHC containing fibers in both muscles and of alpha-cardiac MyHC positive fibers in RH (P < 0.05). The LDH/CS ratio decreased dramatically (P < 0.001) after restriction, to a greater extent in LL than in RH. These changes denoted a more oxidative metabolism using fewer carbohydrates and more lipids in restricted pigs, as suggested by the increased activity of HAD (P < 0.001) and decreased respiratory quotient (P < 0.001).

The accurate classification of skeletal muscle fiber types according to myosin heavy chain (MyHC) polymorphism remains a difficult task in the pig. Combined myofibrillar ATPase and metabolic enzyme histochemistry, in situ hybridization, and immunocytochemistry were performed on serial transverse sections of pig longissimus (L) and rhomboideus (R) muscles at 100 kg body weight to give a new insight into muscle fiber typing in the pig. Several monoclonal antibodies (MAbs) either specific for a single MyHC (I, IIa, or IIb) or of multiple MyHCs (IIa + IIx or I + IIx + IIb) were used. No monospecific IIx antibody was available for the pig. All three adult Type II isoforms were expressed in the white L muscle, whereas no IIb was observed in the red R muscle, which was confirmed using RNase protection analysis. In most fibers, the distribution of the transcripts closely matched that of the corresponding proteins. When observed, co-expression of MyHCs mostly occured for IIx and IIb in L muscle, and was more common at the protein (11.5%) than at the mRNA (2.2%) level. A minor proportion of myofibers showed a mismatch between MyHC mRNA and protein. According to the type grouping distribution of myofibers encountered in pig muscle, MyHC isoform expression followed the rank order of I-->IIa-->IIx-->IIb from the center to the periphery of the islets, concomitantly with a decrease in oxidative metabolism and an increase in fiber size. The developmental origin and functional significance of the type grouping distribution are discussed.

Cet article fait partie du dossier : Caractérisation des différents types de fibres musculaires dans plusieurs espèces : production et utilisation d’anticorps monoclonaux dirigés contre les chaînes lourdes de myosine rapide IIa et IIb

A total of 383 barrows and gilts from a French Large White experimental herd were slaughtered at 100 kg BW. Samples of longissimus muscle were taken to categorize myofibers according to their contractile (I, IIA, and IIB) and metabolic (oxidative and nonoxidative) properties. Myofiber percentages, cross-sectional areas (CSA), and relative areas were measured. Growth rate, carcass composition, muscle chemical composition, metabolic enzyme activities, and meat quality traits were also measured to estimate phenotypic and genetic correlations between these traits and myofiber characteristics. Genetic parameters were estimated using a REML procedure applied to an individual animal model. Heritabilities of fiber traits were moderate to high (h2 = .20 to .59). Highest heritabilities were found for type I fiber percentage (h2 = .46 +/- .11), type IIBw fiber percentage (h2 = .58 +/- .11), and type I fiber cross-sectional area (h2 = .59 +/- .10). For a given fiber type, the relative area was phenotypically and genetically more closely related to the percentage than to the CSA. Phenotypic correlations between fiber type composition and other traits were low. Genetically, growth rate, carcass leanness, and loin eye area were positively related to fiber CSA. Intramuscular fat content was not related to fiber type composition (r(g) = -.05 to .06), whereas it was positively related to fiber CSA (r(g) = .68). Type IIBw fiber percentage was related to pH at 30 min (r(g) = -.46), pH at 24 h (r(g) = -.62), glycolytic potential (r(g) = .31), and lightness of color (r(g) = .55) of longissimus muscle.

Cet article fait partie du dossier : Le déterminisme génétique du développement musculaire

Agonistic behavior, neuroendocrine and plasma metabolite changes, and muscle glycogen content were studied in 16 fed and 16 24 h-fasted domestic Large White pigs (100 +/- 5 kg) submitted to dyadic encounters (30 min) in a novel environment. Comparisons were made with corresponding control pigs (eight fed and eight 24 h-fasted animals) kept under resting conditions. At rest, fasting resulted in a significant decrease in plasma insulin, increase in plasma-free fatty acids, and decrease in glycogen content in the predominantly red Semispinalis muscle. Fasted pigs displayed significantly more submissive acts than fed ones. In response to dyadic encounters, fed and fasted pigs showed similar rise in plasma levels of cortisol, catecholamines, and lactate, but stress-induced hyperglycemia was suppressed in food-deprived animals. Fasting enhanced stress-induced glycogen depletion in the predominantly white Longissimus muscle but this effect was significant only in fast-twitch glycolytic fibres (alpha W). In the Semispinalis of fasted pigs, however, dyadic encounters did not induce further glycogen depletion. The present findings suggest that in response to dyadic encounters, fasting-induced changes in glucose metabolism lead to a higher dependence on endogenous energy reserves, i.e., glycogen, in working muscles.

The glycogenolytic effect of exogenous epinephrine was studied in white (Longissimus) and red (Trapezius) muscle of anaesthetized pig. In addition, we assessed the metabolic action of epinephrine during the 3 h following the cessation of perfusion. Twelve purebred Large White pigs, averaging 80 kg liveweight, were used. The animals were anaesthetized and perfused (0-15 min) with 5 mu g kg(-1) min(-1) epinephrine or saline (control animals). Blood samples were taken to determine plasma levels of glucose, lactate and non-esterified fatty acids (NEFA). Muscle samples were taken to determine the concentrations of glycogen and related metabolites, and the activity ratio of the enzyme glycogen phosphorylase. Control animals showed stable levels of plasma and muscle metabolites during the 3 h anaesthesia. However, the resting level of the activity ratio of phosphorylase was high (80%). Epinephrine treatment induced significant increases in plasma metabolites and an overall significant glycogen depletion. The extent of epinephrine-induced glycogenolysis was greater in the red Trapezius than in the white Longissimus muscle. This was associated with a greater rise in the muscle lactate content and in the activity ratio of phosphorylase in the Trapezius muscle during epinephrine administration. In both muscles, no significant glycogen depletion was observed during 3 h following the cessation of epinephrine administration. This occurred despite the fact that the activity ratio of phosphorylase remained high in the Longissimus muscle until the end of the experiment.

The present study was designed to examine the lipid composition of a predominantly glycolytic (M. longissimus lumborum, LL) and a predominantly oxidative (M. semispinalis capitis, SC) muscle sampled at slaughter from Large White pigs fed or deprived of food for 24 h. The intramuscular lipid content was almost four-fold higher in the red SC than in the white LL. When expressed on a muscle tissue basis, the results indicated that the LL had significantly lower amount of tri-, di- and monoglycerides, free fatty acids, cholesterol and phospholipids than the SC. In both muscles, phosphatidylcholine represented the major constituent of the phospholipid fraction. The difference in phospholipid content between the LL and the SC was significant only for cardiolipin, phosphatidylethanolamine and phosphatidylinositol. When expressed on total lipid basis, the results showed that the SC contained significantly lower amount of phospholipids and higher amount of triglycerides than the LL, thus suggesting that the influence of muscle type on the content of intramuscular lipid was primarily due to a difference in the amount of triglycerides. Food deprivation for 24 h resulted in a significantly higher content of free fatty acids, as expressed on a muscle tissue basis, in both muscles. Relative to total lipid, food deprivation resulted in increased levels of free fatty acids and monoglycerides only in the LL. These results suggest that food deprivation for 24 h induced lipolysis in muscle, as evidenced by a modification in the relative composition of the neutral lipid fraction, but that this effect was muscle-dependent.

The aim of this study was to analyze the temporal sequence of expression of the myosin isoforms in the populations of muscle fibers in the pig and to bring more information on the origin of the strikingly different pattern of fiber composition and distribution between the deep medial red (oxido‐glycolytic) and superficial white (glycolytic) portions of semitendinosus (ST) muscle. Muscle samples were taken from 49‐, 55‐, 75‐, 90‐, 103‐, and 113‐ (birth) day‐old fetuses, from 6‐, 11‐, 21‐, 35‐, 50‐, and 80‐day‐old piglets, and from a 3‐year‐old pig. Our results confirm the sequential formation of primary and secondary generation fibers. The use of immunohistochemistry and heterologous monoclonal antibodies (mAb) directed against specific myosin heavy chain (MHC) isoforms revealed a different pattern of gene expression between the two portions of the ST muscle for both generations of fibers. By 75 days of gestation (dg), primary myotubes from the deep medial portion stained positively for the anti‐slow MHC mAb and negatively for the adult anti‐fast MHC, whereas the opposite was observed in the superficial portion. Secondary fibers never expressed slow MHC until late gestation. Instead, they expressed an adult fast MHC isoform as soon as they formed in the deep medial portion and later on in the superficial portion. From late gestation to the first 3 postnatal weeks, slow MHC began to be expressed in a subpopulation of secondary fibers. These fibers were in the direct vicinity of primary myotubes in the deep medial portion, whereas their location could not be established in the superficial portion. The remaining secondary fibers matured to type IIA in the direct vicinity of these type I fibers and to type IIB at the periphery of the islets. In both portions of the muscle, a subpopulation of secondary fibers, the first ones to express slow MHC, also transitorily expressed a MHC that was identical or closely related to the αcardiac MHC during the early postnatal period. A third generation of small diameter fibers was observed shortly after birth and reacted with the anti‐fetal MHC mAb; their destiny remains to be established. The present work reveals a remarkable pattern of MHC gene expression in the pig and raises many questions on the real nature of these isoforms. In order to answer these questions, we have undertaken to make a cDNA library of pig skeletal muscle and to screen this library with the same mAbs used in the present study. ©1995 Wiley‐Liss, Inc.

The aim of the present work was to study the effect of fasting times (0, 24, 48 and 72 h) on glycogen level in different fibre types of a predominantly white (Longissimus, LD) and a predominantly red (Semispinalis, SS) pig muscle, and on ultimate pH (pH(u), 24 h post mortem). Thirty two individually housed Large White castrates (eight pigs per treatment) were slaughtered individually under minimal stressful conditions. Muscle samples were taken during bleeding for enzymic determination of muscle metabolites and histological examination using computerised image analysis. Myofibres were classified by a combination of metabolic (W, white; R, red) and contractile (alpha, fast-twitch; beta, slow-twitch) characteristics. The SS showed higher glycogen depletion after 24 h fasting than the LD (-55 versus -26%, respectively). No further significant changes in glycogen level were recorded with enhanced fasting times (up to 72 h), although in the SS a marked trend towards glycogen depletion was observed. Fasting for 24 h resulted in significantly increased pH(u) in the SS whereas for the LD, a significant increase in pH(u) occurred only after 48 h fasting. In response to fasting, significant decrease in histochemical staining intensity for glycogen occurred in the three fibre types of the SS. The beta R fibres of the SS showed an almost complete glycogen depletion after 24 h fasting. With increasing fasting time, glycogen was further depleted in fast-twitch fibres (alpha W and alpha R). In the LD, only fast-twitch fibres exhibited significant decrease in glycogen level after 24 h fasting. However, this was of a much lower magnitude than that observed in the SS and furthermore, no further variation was recorded with increasing fasting time, regardless of fibre type. The present work is the first to report a significant interaction between muscle type and fasting-induced glycogen depletion in pig. Furthermore, these results demonstrate that within each muscle, the extent of fasting-induced glycogen depletion is strongly fibre-type-dependent.

Changes in glycogen content according to fibre type were assessed in a predominantly white (Longissimus) and a predominantly red (Semispinalis) pig muscle, in response to dyadic encounters involving aggressive interactions. Tested animals showed significantly lower glycogen levels than the control in the Semispinalis, but not in the Longissimus muscle. Histological treatment of muscle serial cuts followed by computerized image analysis showed that the observed decrease in muscle Semispinalis glycogen level occurred only in fast-twitch fibres. Total glycogen and glycogen contents in fast-twitch fibres of the Semispinalis muscle were closely and negatively related to aggressive behaviour, but not with plasma epinephrine levels during and at the end of the encounters. The present results provide indirect evidences suggesting a major influence of fighting-induced physical activity on muscle glycogen depletion in response to aggressive interactions in pigs.