Biomechanical analysis of tendon regeneration capacity of Iberian ribbed newts following transection injury: Comparison to a mouse model.

Adult mammals are known for their poor ability to regenerate tissues, including tendons. On the other hand, urodeles have become an important model in regenerative studies for their remarkable ability to regenerate various body parts and organs throughout life, such as limbs, retinas, or even the brain. However, little is known about their capacity to regenerate injured tendons. If newts can also repair tendons without scar formation, they may be a suitable animal model for tendon regeneration studies in other adult vertebrates. Therefore, the present study used Iberian ribbed newts to characterize mechanical and structural regeneration of tendons following transection, using tensile tests and multiphoton microscopy. A digital flexor tendon in a hindlimb was transected either partially or completely, and regenerated tendon was examined 6 and 12 weeks after the operation. Tensile strength of regenerated tendons was significantly less than normal at 6 weeks, but was remarkably recovered at 12 weeks, reaching levels comparable to those of uninjured tendons. On the other hand, mouse tendons demonstrated poor recovery of strength even after 12 weeks. Multiphoton microscopy revealed that tendon-like collagenous tissue bridges residual tendon stubs in newts, but disorganized scar-like tissue filled the injured location in mice. These findings highlight the remarkable capacity of newts to recover from tendon injury and confirm the utility of newts as a model to study tendon regeneration.

Mechanism of skeletal muscle atrophy by muscle fiber types in male rats under long-term fasting stress.

Fasting induces metabolic changes in muscles, which are differentiated by muscle fiber type. In this study, the mechanism of fasting-induced muscle atrophy in rats was examined to determine the differences between muscle fiber types in energy production. Fasting for 96 h did not alter the weight of the soleus (SOL), a fiber type I muscle, but did significantly reduce the weight of gastrocnemius (GM), a fiber type II muscle. GM, SOL and blood pregnenolone and testosterone levels decreased under fasting, which induced energy deprivation, whereas corticosterone (CORT) levels significantly increased. However, the expression of 3ß-HSD and P45011ß in GM was unaffected by fasting. The decrease in GM weight may be due to decreased levels of testosterone and reduced synthesis of mammalian target of rapamycin (mTOR). Significant increases in CORT both GM and SOL were associated with increases in the amount of branched-chain amino acids available for energy production. However, decreased levels of mTOR and IGF1 and increased levels of CORT and IL-6 in SOL suggest that GM proteolysis was followed by SOL proteolysis for additional energy production. In conclusion, IGF1 levels decreased significantly in SOL, whereas those of IL-6 significantly increased in SOL and blood but decreased in GM. Blood branched-chain amino acids (BCAA) levels were unaffected due to fasting, whereas an increase was noted in the levels of BCAA in GM and SOL. These results show that fasting for 96 h restricts energy supply, producing fast-twitch muscle atrophy followed by slow-twitch muscle atrophy.

Characteristics of Mycoplasma bovis, Mycoplasma arginini, and Mycoplasma californicum on immunological response of bovine synovial cells.

Mycoplasma arthritis in calves caused by M. bovis exhibits joint swelling, lameness, and immobility. In contrast to M. bovis, M. arginini, and M. californicum which were similarly isolated from the affected joints, only induced mild inflammation. The changes in pathogenesis that depended on species, however, remained unknown. This investigation aims to examine the characteristics of immune responses to M. bovis, M. arginini, and M. californicum in synovial cells. Intracellular M. bovis was detected by gentamicin assay, but M. arginini and M. californicum were not detected. M. bovis-infected synovial cells were encouraged to proliferate and had their apoptosis suppressed. We suggest that M. bovis invaded and inhibited apoptosis of synovial to evade host immunity, which led to long term survival in joints. M. bovis infection significantly increased IL-6 mRNA expression compared to control, although M. arginini and M. californicum infection were comparable to control. We suggest that M. arginini and M. californicum have low abilities to induce inflammation in joints and therefore do not cause severe pathology. Our findings are the first to show the variations in synovial cell immune responses to M. bovis, M. arginini, and M. californicum, which are thought to be related to the pathogenicity of arthritis.

Physicochemical properties of wooden breast-extracted myosin and rheological properties of its heat-induced gel.

BACKGROUND: It is reported that broilers with 'wooden breast' have poor processing properties, such as low binding and water-holding capacities. However, the reason for the poor functional characteristics has not been clarified. In this study, myosin was extracted from a wooden breast. Its physicochemical properties were investigated to clarify the relationship between the structure and physicochemical properties of the heating gel of myosin obtained from the wooden breast. RESULTS: The turbidity of myosin solution extracted from wooden breast increased with increase in the heat treatment to a higher value than that from the normal breast meat myosin. The solubility of myosin collected from a wooden breast after heating decreased like normal breast muscle myosin. The surface hydrophobicity of myosin removed from wooden breast increased continually above 60 °C, unlike the change in surface hydrophobicity of normal breast myosin. The free thiol group of myosin extracted from the wooden breast was higher than normal breast myosin before and after heating. The apparent elasticity of heat-induced gels and chicken meat sausages was significantly lower in sausages and gel with wooden breast than normal ones (P < 0.05). The microstructure of the heated gel of normal myosin showed a fine network structure. In contrast, the heat-induced gel of wooden breast-extracted myosin showed a structure with loosely connected aggregates and many gaps. CONCLUSION: The coarseness of the internal gel structure of myosin extracted from wooden breast was shown to affect the apparent elasticity of the gel and sausages made from the chicken meat. © 2023 Society of Chemical Industry.

Oviduct Histopathology of Internal Laying and Egg-Bound Syndrome in Laying Hens.

In the egg industry, common reproductive disorders, such as internal laying and egg-bound syndrome, not only reduce egg productivity but also cause deaths in severe cases. In this study, we focused on the oviduct histology of the pathogenesis of internal laying and egg-bound syndrome. We divided the aged laying hens into four groups according to the observation of the abdominal cavity and oviductal lumen: healthy, internal laying, egg-bound, and intercurrent. The percentages of healthy, internal laying, egg-bound, and intercurrent groups were 55%, 17.5%, 15%, and 12.5%, respectively. In all parts of the oviduct (i.e., infundibulum, magnum, isthmus, and uterus), the oviductal epithelium was composed of ciliated epithelial cells and secretory cells. The epithelial region lacking cilia was larger in the entire oviduct of the internal laying, and intercurrent groups than in the healthy group. In the internal laying, egg-bound, and intercurrent groups, significant T-cell infiltration was observed in the lamina propria of the entire oviduct. The morphological alteration of ciliated epithelial cells in the oviducts caused by inflammation may be the underlying cause of the pathogenesis of internal laying and egg-bound syndrome.

Decreased Immunoreactivity of Hepatitis E Virus Antigen Following Treatment with Sakhalin Spruce (Picea glehnii) Essential Oil.

The hepatitis E virus (HEV) causes a common infectious disease that infects pigs, wild boars, deer, and humans. In most cases, humans are infected by eating raw meat. Some essential oils have been reported to exhibit antiviral activities. In this study, in order to investigate the anti-HEV properties of essential oils, the immunoreactivities of HEV antigen proteins against the relevant antibodies were analyzed after the HEV antigens underwent treatment with various essential oils. The essential oils extracted from the tea tree, which was previously reported to exhibit antiviral activity, lavender, and lemon had strongly reduced activity. We found that treatment with the essential oil prepared from Sakhalin spruce was associated with the strongest reduction in immunoreactivity of HEV antigen protein(s) among the tested substances. The main volatile constituents of Sakhalin spruce essential oil were found to be bornyl acetate (32.30 %), α-pinene (16.66 %), camphene (11.14 %), camphor (5.52 %), ß-phellandrene (9.09 %), borneol (4.77 %), and limonene (4.57 %). The anti-HEV properties of the various components of the essential oils were examined: treatment with bornyl acetate, the main component of Sakhalin spruce oil, α-pinene, the main component of tea tree oil, and limonene, the main component of lemon oil, resulted in a strong reduction in HEV antigen immunoreactivity. These results indicate that each main component of the essential oils plays an important role in the reduction of the immunoreactivity of HEV antigen protein(s); they also suggest that Sakhalin spruce essential oil exhibits anti-HEV activity. In a formulation with the potential to eliminate the infectivity of HEV in foodborne infections, this essential oil can be applied as an inactivating agent for meat processing and cooking utensils, such as knives and chopping boards.

Biological properties of Staphylococcus virus ΦSA012 for phage therapy.

Staphylococcus virus ΦSA012 has a wide host range and efficient lytic activity. Here, we assessed the biological stability of ΦSA012 against temperature, freeze-thawing, and pH to clinically apply the phage. In addition, inoculation of ΦSA012 through i.p. and i.v. injections into mice revealed that phages were reached the limit of detection in serum and accumulated notably spleens without inflammation at 48 h post-inoculation. Furthermore, inoculation of ΦSA012 through s.c. injections in mice significantly induced IgG, which possesses neutralizing activity against ΦSA012 and other Staphylococcus viruses, ΦSA039 and ΦMR003, but not Pseudomonas viruses ΦS12-3 and ΦR18 or Escherichia viruses T1, T4, and T7 in vitro. Immunoelectron microscopic analysis showed that purified anti-phage IgG recognizes the long-tail fiber of staphylococcus viruses. Although S. aureus inoculation resulted in a 25% survival rate in a mouse i.p. model, ΦSA012 inoculation (i.p.) improved the survival rate to 75%; however, the survival rate of ΦSA012-immunized mice decreased to less than non-immunized mice with phage i.v. injection at a MOI of 100. These results indicated that ΦSA012 possesses promise for use against staphylococcal infections but we should carefully address the appropriate dose and periods of phage administration. Our findings facilitate understandings of staphylococcus viruses for phage therapy.

Sodium butyrate administration modulates the ruminal villus height, inflammation-related gene expression, and plasma hormones concentration in dry cows fed a high-fiber diet.

The objectives of this study were to evaluate the effects of sodium butyrate on the ruminal villus morphology, mRNA expression associated with nutrient metabolism and inflammation in the ruminal epithelium, and plasma concentrations of metabolites and hormones in non-lactating cows fed a high-fiber diet. Four Holstein cows with a rumen cannula were assigned to two treatments in a crossover design. The treatments were ruminal administration of sodium butyrate premix or control premix before feeding to cows fed the same total mixed ration mainly composed of glass silage once a day. Sodium butyrate was provided at a butyrate dose of 0.04% per kg body weight. The control premix was made by replacing sodium-butyrate with wheat bran. The plasma ß-hydroxybutyrate concentration increased 3 to 6 h after the butyrate premix administration but returned to a concentration similar to that of the control before feeding. After continuous administration, increases in the ruminal villus height and plasma concentration of glucagon-like peptide-2, and lower gene expression of TNF-α, IL-1ß, and TLR-2 in the rumen epithelium were observed in cows supplied with the butyrate premix. These results showed that sodium butyrate affects rumen epithelial morphology and plasma concentrations of hormones even under a low fermentable diet.

Immune Response in Chickens Vaccinated with Freeze-Thawed or Warmed Water-in-Oil Vaccine.

This study investigated whether freezing or warming water-in-oil (W/O) vaccines affected the immune responses of chickens. One of the conditions affecting the efficacy of commercially available animal vaccines is the storage temperature range. Previous studies have shown that the properties of some inactivated vaccines change owing to freezing, leading to reduced immune responsiveness after inoculation. In this study, we first determined the freezing temperatures of a commercial W/O vaccine using freezers maintained at -10, -13, -15, and -20°C. The results showed that the W/O vaccine froze from -10 to -12°C. Next, we evaluated the effect on antibody level transitions (sample-to-positive ratio) in 46-day-old broiler chickens vaccinated with the W/O vaccine that was maintained at -20°C, 5°C, and -10°C, in that order. In addition, the effect on antibody value transitions was evaluated in 45-day-old broiler chickens vaccinated with the W/O vaccines that were frozen and thawed between -20°C and 5°C repeatedly or warmed to 45°C. In these experiments, no remarkable effect of the freeze-thawing or warming treatments on antibody value transitions was observed. These results suggested that the efficacy of the W/O vaccine was not significantly affected when placed in a frozen environment or left in a room temperature environment of 42°C or lower for approximately 5 d. These data indicate the possibility of expanding the temperature range for handling W/O vaccines.

The location of protein oxidation in dystrophic skeletal muscle from the mdx mouse model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a severe childhood disease characterised by progressive muscle wasting caused by widespread myofibre necrosis. Implicated in the pathology of DMD is oxidative stress, caused by excessive generation of reactive oxygen and nitrogen species (RONS). One consequence of RONS exposure is post-translational oxidative modifications to proteins, which can cause loss of protein function. This study used the dystrophic mdx mouse model for DMD to visualise the precise location of different oxidative modifications to proteins in dystrophic muscles, including both reversible (protein thiol oxidation and s-nitrosylation) and irreversible (carbonylation and dityrosine formation) oxidation at various stages of dystrophic muscle necrosis and regeneration. High levels of protein oxidation were observed in mdx myofibres undergoing degeneration and immune cell infiltration (myonecrosis). Since irreversible protein oxidation, especially dityrosine formation, was only colocalised to areas of myonecrosis, we suggest that this specific measurement could be a useful biomarker of myonecrosis. To test this we quantified dityrosines in muscle homogenates; this analysis showed significantly higher levels of dityrosines in mdx (compared with control normal) mice aged 23 days, an age when acute onset of extensive myonecrosis occurs in mdx muscles. These results indicate a major localised role of immune cells in RONS generation in dystrophic muscle, and strongly support a role for protein oxidation in myonecrosis and associated dystropathology. Consequently, the measurement of protein oxidation (specifically dityrosines) in dystrophic muscles may be a useful biomarker for indirectly quantifying myonecrosis in research studies using mdx mice and other animal models for DMD.

Morphological analysis of cell distribution and network structure via gap junctions in swine corneal stroma.

Because of corneal transplantation limitations, there is a need for cornea-specific regenerative medicine. The development of such regenerative medicine has been delayed because of the complex and unique structure of the corneal stroma. Few studies have explored the corneal stroma cell distribution and cell types in vivo. This study investigated regional differences in morphological characteristics and distributions of corneal keratocytes and immunocompetent cells in the corneal stroma to clarify their functions and structural characteristics. The porcine eyeballs were subjected to light microscopy, transmission electron microscopy, scanning electron microscopy, and immunofluorescence staining analyses. Corneal cells were primarily located in the limbus, rather than the center of the cornea; the long keratocyte diameter was largest on the epithelial side of the corneal limbus, while the short diameter was largest on the endothelial side of the central cornea. Moreover, there were significantly more corneal cells on the epithelial side than on the endothelial side in both the central and limbus areas. Gap junctions between cells in the corneal stroma were present on the surfaces of cytoplasmic processes. Many cytoplasmic processes were scattered throughout the corneal stroma; they were connected both vertically and horizontally, forming an intercellular network. Additionally, immunocompetent cells on the epithelial side suggested to participate in this network via gap junctions. The morphology of keratocytes and immunocompetent cells on the epithelial side suggests that they play important roles in corneal homeostasis.

Mitochondrial characteristics of chicken breast muscle affected by wooden breast.

The growth rate of broiler chickens has increased by 400% over the past 50 years, and breast yields continue to increase. This has led to an increase in thoracic muscle abnormalities in broilers, with wooden breast becoming a major issue worldwide. The etiology and the mechanism underlying the etiology of wooden breasts have not yet been elucidated; however, it occurs due to oxidative stress. Reactive oxygen species, which cause oxidative stress, are mainly produced in mitochondria. Thus, in this study, we investigated the relationship between the severity of wooden breast in broilers and the characteristics of mitochondria as the source of reactive oxygen species. Sampling of the pectoralis major muscle at the ventral cranial position was conducted in 50-day-old broilers. The severity of wooden breast was classified into three groups based on the muscle fiber roundness and wing-wing contact test, with highest severity in severe wooden breast and lowest severity in normal breast. Nicotinamide adenine dinucleotide tetrazolium reductase staining revealed an increase in darkly stained muscle fibers, indicating high severity of wooden breast. The mitochondria were swollen in severe wooden breast cases, with highest swelling in severe wooden breast and lowest swelling in normal breast. The expression levels of the mitochondrial antioxidant enzyme genes superoxide dismutase 1 and superoxide dismutase 2 were significantly lower in wooden breast-severe tissue than in normal tissue. These results suggest that when the levels of reactive oxygen species in muscle fibers, which should be constant, are increased, mitochondrial homeostasis is not maintained and the damage levels increase in various membranes of the cell, leading to the disruption of normal physiological functions.

Three-dimensional structural analysis of mitochondria composing each subtype of fast-twitch muscle fibers in chicken.

In a previous study, the three-dimensional structures of mitochondria in type I and type IIb muscle fibers of chicken were analyzed. The study reported differences in the shape of the mitochondria and the distribution of lipid droplets. In this study, we three-dimensionally analyzed mitochondria and lipid droplets of type II muscle fiber subtypes IIa, IIb, and IIc of chicken lateral iliotibial muscle in the same field of view using correlative light electron microscopy (CLEM) and array tomography methods. The reconstructed images showed that the mitochondria of type IIa muscle fiber were thick and aligned along the myofibrils, and many lipid droplets were embedded in the mitochondria. The mitochondria of type IIb muscle fibers were intermittent, aligned along the myofibrils, and showed contact between adjacent horizontal mitochondria. No lipid droplets were observed in type IIb muscle fiber. In type IIc muscle fiber, we observed irregularly shaped mitochondria with small diameters aligned along the myofibrils. Lipid droplets not only were embedded in the mitochondria but also existed independently in some cases. The combination of array tomography and CLEM methods enabled three-dimensional electron microscopic observation of mitochondria in different subtypes of type II muscle fibers. The subtypes of type II muscle fibers differed in mitochondrial occupancy and morphology and in lipid droplet distribution, and characteristics that had been demonstrated biochemically were also demonstrated ultrastructurally.

Whole-Genome Sequencing of Pasteurella multocida Strain Pm1, Isolated from a Calf.

Bovine pneumonia is a disease that causes significant economic losses in livestock industries and is vital for animal welfare. The whole-genome sequence of Pasteurella multocida strain Pm1, isolated from a calf suffering from pneumonia in Japan, is reported here.

Testicular induced corticosterone synthesis in male rats under fasting stress.

Testicular steroidogenesis is depressed by adrenal-secreted corticosterone (CORT) under stress. However, the mechanisms are not well understood. This study investigated the details of testicular steroidogenesis depression during fasting. Blood levels of adrenocorticotropic hormone secreted from the pituitary glands increased, but blood CORT was not changed in rats that fasted for 96 h, in spite of the rats being severely stressed. CORT in fasting adult male rats increased more than three times in the testis, but reduced testicular testosterone (T) and blood T levels to 5% and 2% of the control, respectively, was observed. The contents of T precursor (except PGN) were drastically reduced in the fasted-rat testes. Testicular CORT levels were elevated, but the enzymatic activity of cytochrome P45011ß, which produces CORT, remained unchanged. The enzymatic activities of 3ß-hydroxysteroid dehydrogenase (3ß-HSD), mediating the conversion of pregnenolone to progesterone, decreased in the fasted-rat testes. Thus, fasting suppressed testicular steroidogenesis by affecting the enzyme activity of 3ß-HSD in the testes and drastically reduced T and increased CORT synthesis. It can be considered that T synthesis involved in cell proliferation is suppressed due to lack of energy during fasting. Conversely, 11ß-hydroxylase enzyme activity was induced and CORT synthesis is increased to cope with the fasting stress. Hence, it can be concluded that CORT synthesis in the testes plays a role in the local defense response.

Structural insights reveal the second base catalyst of isomaltose glucohydrolase.

Glycoside hydrolase family 15 (GH15) inverting enzymes contain two glutamate residues functioning as a general acid catalyst and a general base catalyst, for isomaltose glucohydrolase (IGHase), Glu178 and Glu335, respectively. Generally, a two-catalytic residue-mediated reaction exhibits a typical bell-shaped pH-activity curve. However, IGHase is found to display atypical non-bell-shaped pH-kcat and pH-kcat /Km profiles, theoretically better-fitted to a three-catalytic residue-associated pH-activity curve. We determined the crystal structure of IGHase by the single-wavelength anomalous dispersion method using sulfur atoms and the cocrystal structure of a catalytic base mutant E335A with isomaltose. Although the activity of E335A was undetectable, the electron density observed in its active site pocket did not correspond to an isomaltose but a glycerol and a ß-glucose, cryoprotectant, and hydrolysis product. Our structural and biochemical analyses of several mutant enzymes suggest that Tyr48 acts as a second catalytic base catalyst. Y48F mutant displayed almost equivalent specific activity to a catalytic acid mutant E178A. Tyr48, highly conserved in all GH15 members, is fixed by another Tyr residue in many GH15 enzymes; the latter Tyr is replaced by Phe290 in IGHase. The pH profile of F290Y mutant changed to a bell-shaped curve, suggesting that Phe290 is a key residue distinguishing Tyr48 of IGHase from other GH15 members. Furthermore, F290Y is found to accelerate the condensation of isomaltose from glucose by modifying a hydrogen-bonding network between Tyr290-Tyr48-Glu335. The present study indicates that the atypical Phe290 makes Tyr48 of IGHase unique among GH15 enzymes.

Effects of intra-articular inoculation with Mycoplasma bovis on immunological responses in calf joints.

Mycoplasma arthritis that caused by Mycoplasma bovis exhibit severe lameness. This disease is difficult to cure with antibiotics, but the detailed pathological mechanisms have not been fully clarified. In this study, we examined the effects of intra-articular inoculation with M. bovis on immunological responses in calf joints. We inoculated three calves each with M. bovis or phosphate buffer saline (control) into the right stifle joint and dissected them at 15 days postinoculation. Mycoplasma bovis-inoculated calves exhibited swelling of the stifle joint, increases in synovial fluid, fibrin deposition, and cartilage thinning. Intracellular M. bovis was detected in synovial tissues analyzed by immunohistochemistry and transmission electron microscopy. Messenger RNA expressions of interleukin (IL)-1ß, IL-6, IL-8, IL-12p40, and IL-17A in synovial fluid cells and synovial tissues from M. bovis-inoculated calves were significantly higher than those from control calves. Protein levels of these cytokines in synovial fluid from M. bovis-inoculated calves were markedly higher than those from control calves. Our study clarified that inoculation with M. bovis into the stifle joint induced the production of inflammatory cytokines by synovial fluid cells and synovial tissues, causing a severe inflammatory response in joints. Additionally, M. bovis could invade cells in synovial tissues, which may have aided it in evading antibiotics and host immune surveillance.

Novel Virulent Bacteriophage ΦSG005, Which Infects Streptococcus gordonii, Forms a Distinct Clade among Streptococcus Viruses.

Bacteriophages are viruses that specifically infect bacteria and are classified as either virulent phages or temperate phages. Despite virulent phages being promising antimicrobial agents due to their bactericidal effects, the implementation of phage therapy depends on the availability of virulent phages against target bacteria. Notably, virulent phages of Streptococcus gordonii, which resides in the oral cavity and is an opportunistic pathogen that can cause periodontitis and endocarditis have previously never been found. We thus attempted to isolate virulent phages against S. gordonii. In the present study, we report for the first time a virulent bacteriophage against S. gordonii, ΦSG005, discovered from drainage water. ΦSG005 is composed of a short, non-contractile tail and a long head, revealing Podoviridae characteristics via electron microscopic analysis. In turbidity reduction assays, ΦSG005 showed efficient bactericidal effects on S. gordonii. Whole-genome sequencing showed that the virus has a DNA genome of 16,127 bp with 21 coding sequences. We identified no prophage-related elements such as integrase in the ΦSG005 genome, demonstrating that the virus is a virulent phage. Phylogenetic analysis indicated that ΦSG005 forms a distinct clade among the streptococcus viruses and is positioned next to streptococcus virus C1. Molecular characterization revealed the presence of an anti-CRISPR (Acr) IIA5-like protein in the ΦSG005 genome. These findings facilitate our understanding of streptococcus viruses and advance the development of phage therapy against S. gordonii infection.

The unique physiological features of the broiler pectoralis major muscle as suggested by the three-dimensional ultrastructural study of mitochondria in type IIb muscle fibers.

Typical skeletal muscles are composed of mixed muscle fiber types, which are classified as slow-twitch (type I) and fast-twitch (type II) fibers, whereas pectoralis major muscles (PMs) in broiler chickens are 100% composed of type IIb fast-twitch fibers. Since metabolic properties differ among muscle fiber types, the combination of muscle fiber types is involved in physiological functions and pathological conditions in skeletal muscles. In this study, using serial block-face scanning electron microscopy, we compared three-dimensional (3D) mitochondrial properties in type IIb fibers in broiler PMs and those in type I fibers of broiler gastrocnemius muscles (GMs) heterogeneously composed of slow- and fast-twitch muscle fibers. In type I fibers in the GMs, elongated mitochondria with numerous interconnections to form a substantial network among myofibrils were observed. Along with lipid droplets sandwiched by mitochondria, these features are an adaptation to effective oxidative respiration and constant oxidative damage in slow-twitch muscle fibers. In contrast, type IIb fibers in the PMs showed small and ellipsoid-shaped mitochondria with few interconnections and no lipid droplets, forming a sparse network. The mitochondrial spatial network comprises of active mitochondrial dynamics to reduce mitochondrial damage; therefore, type IIb fibers possess physiologically low capacity to maintain mitochondrial wellness due to static mitochondrial dynamics. Based on 3D mitochondrial properties, we discussed the contrasting physiological functions between type I and IIb fibers and proposed a high contractile power and low stress resistance as unique physiological properties of broiler PMs.

Nutrition During the Early Rearing Period Affects the Incidence of Wooden Breasts in Broilers.

This study aimed to evaluate the relationship between early nutrition and the incidence of wooden breasts (WB) in broilers. Sixteen male and twenty female neonatal ROSS 308 broiler chicks were divided equally into four flocks. From 0-12 days of age, starter diet H, composed of 22.4% crude protein (CP), 6.6% crude fat (CF), 1.25% lysine, 0.48% methionine, and ≥3,070 kcal/kg metabolizable energy (ME), was fed to two flocks, and starter diet L, composed of 19.9% CP, 2.5% CF, 1.04% lysine, 0.38% methionine, and ≥2,930 kcal/kg ME, was fed to the remaining two flocks. All the flocks were fed the same commercial finisher diet, composed of 20.3% CP, 7.5% CF, 1.18% lysine, 0.44% methionine, and ≥3,300 kcal/kg ME, from 12-47 days of age. The birds were weighed every 2-5 days, subjected to a wing-lift test, and histology was conducted on the pectoralis major muscle tissue samples from all the birds necropsied at 47 days of age. Significant differences in the mean body weight between groups H and L were observed during 6-16 days and 24-26 days of age in males and during 6-26 days of age in females. Regarding the score evaluation of the individual lesions reflecting wooden breast, the birds in which back-to-back wing contact was not possible had higher lesion scores than those in which back-to-back wing contact was possible. The absence of back-to-back wing contact appeared more frequently in flocks fed the starter diet L, particularly in males. These results indicate that inappropriate nutrition levels in the starter diet increase the incidence of WB. Therefore, avoiding early nutrition deficits is a cost-effective feeding strategy.