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.

Phenotypic and genetic parameters for longissimus muscle fiber characteristics in relation to growth, carcass, and meat quality traits in large white pigs.

Maternal nutrition and progeny birth weight affect muscle fiber development in the pig, thereby influencing early postnatal growth rate. The objective of the study was to determine the extent to which growth, morphometric characteristics, and area and distribution of slow-oxidative (SO), fast oxidative-glycolytic (FOG), and fast glycolytic (FG) fibers of three muscles (LM = longissimus muscle; RF = rectus femoris; ST = semitendinosus) of slaughter pigs were affected by DE intake level during the first 50 d of gestation. Multiparous Swiss Large White sows were assigned randomly to one of three energy intake treatments: 1) fed 2.8 kg/d of a standard diet (STD; n = 6) containing 10.7 MJ DE/kg; 2) fed 2.8 kg/d of a low-energy diet (LE; n = 5) containing 6.6 MJ DE/kg; or 3) fed 4.0 kg/d of a standard diet (HE; n = 5) containing 10.7 MJ DE/kg (as-fed basis). Sows were subjected to energy intake treatments for the first 50 d of gestation; however, from d 51 to parturition, sows received 2.8 kg/d of the standard diet, and the amount of feed offered each sow during lactation was adjusted according to the litter size. Sows farrowed normally and pig birth weights were recorded. Based on birth weight, the two lightest (1.27 kg; Lt) and two heaviest (1.76 kg; Hvy) barrows and gilts from the 16 litters (n = 64) were selected at weaning and were offered a fixed amount of feed (170 g x BW(0.569)/d) from 25 to 105 kg BW. Regardless of the birth weight, progeny from HE sows grew slower (P < 0.05) during lactation and the growing-finishing period, had a lower (P < 0.05) gain-to-feed ratios, and had higher (P < 0.05) percentages of adipose tissue than pigs born from LE sows. The ST was shorter (P = 0.03) in Lt than in Hvy pigs, and the ST of gilts was heavier (P = 0.01) and had a larger (P = 0.01) girth than the ST of barrows. Overall mean fiber area tended to be larger (P < or = 0.11) in the LM and light portion of the ST of Lt than in Hvy pigs, and was larger (P = 0.03) in the ST of gilts than barrows. The ST of progeny from LE sows had fewer (P < 0.10) FG fibers, which was compensated by either more (P < 0.05) FOG in the light portion of the ST, or more (P < 0.10) SO fibers in the dark portion, and these differences were more pronounced in Lt pigs than in Hvy pigs. Overall, maternal feeding regimen affected muscle fiber type distribution, whereas birth weight and gender affected muscle fiber area.

Effect of early gestation feeding, birth weight, and gender of progeny on muscle fiber characteristics of pigs at slaughter.

In neonatal pigs, the feeding-induced stimulation of protein synthesis in skeletal muscle, but not liver, can be reproduced by insulin infusion when essential amino acids and glucose are maintained at fasting levels. In the present study, 7- and 26-day-old pigs were studied during 1) fasting, 2) hyperinsulinemic-euglycemic-euaminoacidemic clamps, 3) euinsulinemic-euglycemic-hyperaminoacidemic clamps, and 4) hyperinsulinemic-euglycemic-hyperaminoacidemic clamps. Amino acids were clamped using a new amino acid mixture enriched in nonessential amino acids. Tissue protein synthesis was measured using a flooding dose of L-[4-(3)H]phenylalanine. In 7-day-old pigs, insulin infusion alone increased protein synthesis in various skeletal muscles (from +35 to +64%), with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as cardiac muscle (+50%), skin (+34%), and spleen (+26%). Amino acid infusion alone increased protein synthesis in skeletal muscles (from +28 to +50%), also with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as liver (+27%), pancreas (+28%), and kidney (+10%). An elevation of both insulin and amino acids did not have an additive effect. Similar qualitative results were obtained in 26-day-old pigs, but the magnitude of the stimulation of protein synthesis by insulin and/or amino acids was lower. The results suggest that, in the neonate, the stimulation of protein synthesis by feeding is mediated by either amino acids or insulin in most tissues; however, the feeding-induced stimulation of protein synthesis in skeletal muscle is uniquely regulated by both insulin and amino acids.

https://www.physiology.org/doi/pdf/10.1152/ajpendo.00517.2001

Stimulation of protein synthesis by both insulin and amino acids is unique to skeletal muscle in neonatal pigs

Texture, moisture retention, and tenderness of processed muscle foods are influenced by the functionality of myofibrillar protein. Recent studies have revealed large variations in processing quality between red and white muscle groups that can be attributed to differences in the functional properties of myofibrillar protein associated with the type of fiber. Myofibrillar proteins from fast- and slow-twitch fibers exhibit different biochemical and rheological characteristics and form gels with distinctly different viscoelastic properties and microstructures. The existence and wide distribution of the numerous myosin isoforms in different muscle and fiber types contribute to the various functional behaviors of myofibrillar protein. The different sensitivities of fast and slow myofibrillar proteins to pH, ionic environment, temperature, and other external factors have been well documented and illustrate the importance of adjusting meat processing conditions, according to fiber type profile to achieve maximum protein functionalities, and hence, uniform quality of the final muscle foods.

Myofibrillar protein from different muscle fiber types : implications of biochemical and functional properties in meat processing

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 alpha-cardiac 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.(ABSTRACT TRUNCATED AT 400 WORDS)

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aja.1002030104

Pattern of muscle fiber type formation in the pig

The conversion of myofiber types was studied in the masseter, trapezius, longissimus, rectus femoris and vastus intermedius muscles of pigs at birth and 2, 4, 8 and 16 weeks of age. The histochemical reaction for ATPase was used to classify myofibers as type I (acid-stable, alkali-labile) or type II (alkali-stable, acid labile). Type II myofibers were divided further into categories IIA and IIB. Subtypes SM, SS and MS were intermediate to types I and II and were classified on the basis of pH sensitivity of the ATPase reaction. In the longissimus, rectus femoris and masseter muscles, the proportion of type II myofibers decreased and the proportion of type I myofibers increased from birth to 8 weeks of age, and little change occurred thereafter. These three muscles had more type II than type I myofibers, regardless of age. At birth the trapezius and vastus intermedius muscles both and more type II than type I myofibers, but during development, the proportion of type I myofibers increased greatly while that of type II decreased markedly. At 16 weeks, the trapezius had about equal proportions of type II and type l myofibers, but the vastus intermedius had a much higher proportion of type I than type II myofibers. A flow diagram was developed to illustrate the proposed conversion of type II to type I myofibers via the intermediate stages identified as subtypes MS, SS and SM. Development of the type I grouped pattern and the association of myofiber proportions with functions in the masseter muscle are discussed.

A Suzuki

Papers

A histochemical study of myofiber types in muscle of the growing pig.