Genetic selection for high growth rate, breast muscle yield, and feed efficiency in modern broilers has been a double-edged sword. While it has resulted in marked benefits in production, it has also introduced widespread incidence of breast muscle myopathies. Broiler myopathies are phenotypically characterized by myodegeneration and fibrofatty infiltration, which compromise meat quality. These lesions resemble those of various myopathies found in humans, such as Duchenne muscular dystrophy, Limb-girdle muscular dystrophy, and sarcopenia. Fibroadipogenic progenitors (FAPs) are interstitial muscle-resident mesenchymal stem cells that are named because of their ability to differentiate into both fibroblasts and adipocytes. This cell population has clearly been established to play a role in the development and progression of myopathies in mice and humans. Gene expression studies of wooden breast and other related disorders have implicated FAPs in broilers, but to our knowledge this cell population have not been characterized in chickens. In this review, we summarize the evidence that FAPs may be a novel, new target for interventions that reduce the incidence and development of chicken breast muscle myopathies.

The study investigated guanidinoacetic acid (GAA) supplementation with varying dietary digestible arginine (Arg) and glycine+serine (Gly+Ser) concentrations in the starter phase, exploring respective carry-over effects on growth performance, blood chemistry, incidence of pectoral myopathies and proximate composition in broilers. A total of 2,800 one-day-old male broiler chicks were distributed in a central composite design with 2 factors and double experimental mesh, represented by supplementation or omission of 0.6 g per kg of GAA, with a central point represented by 107% of Arg and 147% of Gly+Ser, 4 factorial points (combinations of Arg/Gly+Ser concentrations: 96.4/132.5%; 117.6/132.5%; 96.4/161.5%, and 117.6/132.5%), and 4 axial points (combinations of axial points estimated for Arg and Gly+Ser, with the central points of 92/147%; 122/147%; 107/126.5, and 107/167.5%), totaling 18 treatments, 4 repetitions to factorial and axial points, 24 replicates to the central point, and 25 birds per pen. Feed conversion ratio (FCR) from d 1 to 10 had a linear response (P = 0.009) for the decreasing Arg content and a quadratic response (P = 0.047) for Gly+Ser concentrations. Broilers supplemented GAA had lower FCR compared with nonsupplemented groups from d 1 to 10 (P = 0.048) and d 1 to 42 (P = 0.026). Aspartate aminotransferase (AST) exhibited increasing and decreasing linear effects as a function of Arg (P = 0.008) and Gly+Ser (P = 0.020) concentrations, respectively. Guanidinoacetic acid decreased serum AST (P = 0.028). Guanidinoacetic acid reduced moderate + severe (P = 0.039) and mild (P = 0.015) Wooden Breast scores. The occurrence of normal White Striping increased (P = 0.002), while severe score was reduced (P = 0.029) with GAA supplementation. In conclusion, increased digestible Arg:Lys and 14% and 6% above the recommendations (107% and 147%), respectively, provided improved FCR during the starter phase. Dietary GAA supplementation (0.6 g per kg) improved FCR, reduced severity of breast myopathies and appears to have reduced muscle damage in broilers fed plant-based diets.

Wooden breast (WB) is a myopathy mainly affecting pectoralis major (PM) muscle in modern commercial broiler chickens, causing enormous economic losses in the poultry industry. Recent studies have observed hepatic and PM muscle injury in broilers affected by WB, but the relationships between WB and the 2 tissues are mostly unclear. In the current study, the RNA-seq raw data of PM muscle and liver were downloaded from GSE144000, and we constructed the gene coexpression networks of PM muscle and liver to explore the relationships between WB and the 2 tissues using the weighted gene coexpression network analysis (WGCNA) method. Six and 2 gene coexpression modules were significantly correlated with WB in the PM muscle and liver networks, respectively. TGF-beta signaling, Toll-like receptor signaling and mTOR signaling pathways were significantly enriched in the genes within the 6 gene modules of PM muscle network. Meanwhile, mTOR signaling pathway was significantly enriched in the genes within the 2 gene modules of liver network. In the consensus gene coexpression network across the 2 tissues, salmon module (r = -0.5 and p = 0.05) was significantly negatively correlated with WB, in which Toll-like receptor signaling, apoptosis, and autophagy pathways were significantly enriched. The genes related with the 3 pathways, myeloid differentiation primary response 88 (MYD88), interferon regulatory factor 7 (IRF7), mitogen-activated protein kinase 14 (MAPK14), FBJ murine osteosarcoma viral oncogene homolog (FOS), jun proto-oncogene (JUN), caspase-10, unc-51 like autophagy activating kinase 2 (ULK2) and serine/threonine kinase 11 (LKB1), were identified in salmon module. In this current study, we found that the signaling pathways related with cell inflammation, apoptosis and autophagy might influence WB across 2 tissues in broilers.

Wooden breast (WB) myopathy is a common myopathy found in commercial broiler chickens worldwide. Although extensive research on WB has been conducted using transcriptomics, effectively screening and analyzing key target information remains a challenge. In this present study, 5 transcriptomic datasets obtained from the National Center for Biotechnology Information (NCBI) were used. A meta-analysis was conducted to identify meta-differentially expressed genes (meta-DEGs) involved in the response of broilers to WB myopathy. These meta-DEGs were further analyzed using Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Ontology (GO), and Gene Set Enrichment Analysis (GSEA), supplemented by protein-protein interaction (PPI) network construction to pinpoint hub genes. These analyses help to reveal key genes, pathways, and biological processes associated with WB myopathy. The results showed that 645 up-regulated and 99 down-regulated significant meta-DEGs (|log2FC| ≥0.6, P-Meta < 0.05, and present in at least 4 datasets) were identified. GO analysis showed that multiple fibrosis-related pathways/biological processes, such as cell adhesion, connective tissue development, and collagen-rich extracellular matrix, as well as calcium ion binding were significantly upregulated. PPI analysis identified TGFB3, COL1A1, COL1A2, and COL3A1 as central hub genes involved in the fibrotic processes. KEGG analysis revealed significant upregulation of apoptosis and lysosomal pathways, with an enrichment of Ca2+-related signals and lysosomal cathepsins within the apoptosis pathway. Additionally, GSEA indicated a suppression of the tricarboxylic acid (TCA) cycle and the mitochondrial electron transport chain (ETC) in WB myopathy, with PPI analysis also identifying specific hub genes associated with these pathways. In conclusion, our comprehensive analysis of meta-DEGs elucidated key biological processes and pathways implicated in WB myopathy, including fibrosis, apoptosis, altered calcium signaling, and metabolic disruption. The identification of specific hub genes offers avenues for further investigation into the pathogenesis of this condition, potentially guiding targeted therapeutic strategies.

Wooden Breast (WB) abnormality represents one of the major challenges that the poultry industry has faced in the last 10 years. Despite the enormous progress in understanding the mechanisms underlying WB, the precise initial causes remain to be clarified. In this scenario, the present research is intended to characterize the gene expression profiles of broiler Pectoralis major muscles affected by WB, comparing them to the unaffected counterpart, to provide new insights into the biological mechanisms underlying this defect and potentially identifying novel genes likely involved in its occurrence. To this purpose, data obtained in a previous study through the RNA-sequencing technology have been used to identify differentially expressed genes (DEGs) between 6 affected and 5 unaffected broilers\' breast muscles, by using the newest reference genome assembly for Gallus gallus (GRCg7b). Also, to deeply investigate molecular and biological pathways involved in the WB progression, pathways analyses have been performed. The results achieved through the differential gene expression analysis mainly evidenced the downregulation of glycogen metabolic processes, gluconeogenesis, and tricarboxylic acid cycle in WB muscles, thus corroborating the evidence of a dysregulated energy metabolism characterizing breasts affected by this abnormality. Also, genes related to hypertrophic muscle growth have been identified as differentially expressed (e.g., WFIKKN1). Together with that, a downregulation of genes involved in mitochondrial biogenesis and functionality has been detected. Among them, PPARGC1A and PPARGC1B chicken genes are particularly noteworthy. These genes not only have essential roles in regulating mitochondrial biogenesis but also play pivotal roles in maintaining glucose and energy homeostasis. In view of that, their downregulation in WB-affected muscle may be considered as potentially related to both the mitochondrial dysfunction and altered glucose metabolism in WB muscles, and their key involvement in the molecular alterations characterizing this muscular abnormality might be hypothesized.

This study aims to provide new insight on the association between the development of wooden breast myopathy and mitochondrial and glycolytic activity under oxidative stress. Myopathic muscle had higher oxidative stress together with altered glycolytic metabolism and tricarboxylic acid (TCA) cycle. This was evidenced by significantly elevated antioxidant enzyme activities (catalase, superoxide dismutase, and glutathione peroxidase), decreased citrate synthase activity and postmortem glycolytic potential with increasing wooden breast severity. In addition, affected muscles also exhibited higher initial and ultimate pH values as well as reduced total glucose and lactate contents. Citrate synthase activity was negatively correlated to antioxidant enzyme activities. Taken together, we propose that the development of the wooden breast lesion is a chronic process that may be related to the failure of muscle fibers to defend against the excessively generated oxidative products promoted by mitochondrial damage accompanied by impaired TCA cycle. Furthermore, there was a positive correlation between citrate synthase activity and glycolytic potential, which suggests that the wooden breast condition is linked to the overall altered energy metabolism of the muscle, including the oxidative phosphorylation and glycolytic pathways.

BACKGROUND: Wooden breast (WB) myopathy is a common myopathy found in commercial broiler chickens worldwide. Histological examination has revealed that WB myopathy is accompanied by damage to the pectoralis major (PM) muscle. However, the underlying mechanisms responsible for the formation of WB in broilers have not been fully elucidated. This study aimed to investigate the potential role of hypoxia-mediated programmed cell death (PCD) in the formation of WB myopathy.
RESULTS: Histological examination and biochemical analysis were performed on the PM muscle of the control (CON) and WB groups. A significantly increased thickness of the breast muscle in the top, middle, and bottom portions (P<0.01) was found along with pathological structure damage of myofibers in the WB group. The number of capillaries per fiber in PM muscle, and the levels of pO2 and sO2 in the blood, were significantly decreased (P < 0.01), while the levels of pCO2 and TCO2 in the blood were significantly increased (P < 0.05), suggesting hypoxic conditions in the PM muscle of the WB group. We further evaluated the PCD-related pathways including autophagy, apoptosis, and necroptosis to understand the consequence response to enhanced hypoxic conditions in the PM muscle of birds with WB. The ratio of LC3 II to LC3 I, and the autophagy-related factors HIF-1α, BNIP3, Beclin1, AMPKα, and ULK1 at the mRNA and protein levels, were all significantly upregulated (P < 0.05), showing that autophagy occurred in the PM muscle of the WB group. The apoptotic index, as well as the expressions of Bax, Cytc, caspase 9, and caspase 3, were significantly increased (P < 0.05), whereas Bcl-2 was significantly decreased (P < 0.05) in the WB-affected PM muscle, indicating the occurrence of apoptosis mediated by the mitochondrial pathway. Additionally, the expressions of necroptosis-related factors RIP1, RIP3, and MLKL, as well as NF-κB and the pro-inflammatory cytokines TNF-α, IL-1β, and IL-6, were all significantly enhanced (P < 0.05) in the WB-affected PM muscle.
CONCLUSIONS: The WB myopathy reduces blood supply and induces hypoxia in the PM muscle, which is closely related to the occurrence of PCD including apoptosis, autophagy, and necroptosis within myofibers, and finally leads to abnormal muscle damage and the development of WB in broilers.

Wooden breast (WB) myopathy is a pathology of the pectoralis major muscle. Wooden breast is caused by multiple factors. The exact etiopathogenesis of this myodegenerative pathology is still unclear. Fast-growing commercial lines of broilers that are selected for high breast muscle yields are more susceptible to this myopathy. The biochemical analysis of blood is used to diagnose pathologies and understand disease processes. Therefore, the objective of this research was to determine and compare the changes in the blood serum biochemical parameters of Ross 308 chicken broilers without myopathy and those affected by WB myopathy. Blood samples were collected from male and female Ross 308 broilers that were 43 days old, with an average live weight of 2.98-3.09 kg. Representative blood samples were selected from broilers with WB (n = 33) and without WB (n = 33). In the laboratory, the blood was centrifugated, and biochemical tests were performed with an automated computerized biochemistry analyzer. The research results showed that broilers with WB had elevated blood serum levels of creatine kinase (CK) (p = 0.018), potassium (p = 0.010), and alanine aminotransferase (ALT) (p = 0.012). In conclusion, elevated serum levels of CK and potassium indicated that skeletal muscle cells were damaged. Moreover, increased ALT levels suggested a possible association between WB myopathy and liver damage. Additionally, these research findings underscore the diagnostic significance of CK and hint at its potential as a WB biomarker.

The Wooden Breast myopathy results in the necrosis and fibrosis of breast muscle fibers in fast-growing heavy weight meat-type broiler chickens. Myogenic satellite cells are required to repair and regenerate the damaged muscle fibers. Using Genome Wide Association, candidate genes affected with Wooden Breast have been previously reported. The effect of these genes on satellite cell proliferation, differentiation, and the synthesis of lipids by satellite cells is unknown. Satellite cells isolated from the pectoralis major muscle from commercial Ross 708 broilers and a Randombred chicken (RBch) line were used. Expression of calponin 1 (CNN1) and PHD and ring fingers domains 1 (PHRF1) were knocked down by silent interfering RNA to determine their effect on satellite cell-mediated proliferation, differentiation, and lipid accumulation. CNN1 and PHRF1 affected satellite cell activity and lipid accumulation in both lines. Proliferation was reduced in the Ross 708 and RBch lines by knocking down the expression of both genes, and differentiation was affected with a line and treatment interaction when gene expression was reduced at the beginning of proliferation. During differentiation lipid accumulation was decreased with knocking down the expression of CNN1 and PHRF1. Both CNN1 and PHRF1 have not been reported previously in skeletal muscle and further research is required to determine their effect on satellite cell-mediated growth and regeneration of the pectoralis major (breast) muscle.

1. This study investigated the relationships of quality indices with the severity of wooden breast (WB) myopathy in chicken breast meat under refrigerated storage. The physicochemical properties, water-holding capacity (WHC), microbial quality and fatty acid profiles of normal chicken breast meat samples (NOR samples, n = 63), moderate WB (MWB, n = 63) myopathy and severe WB (SWB, n = 63) myopathy (MWB and SWB samples, respectively) were evaluated immediately after sampling and after 4 and 8 d of refrigerated storage at 4°C.2. Total collagen, fat, saturated and monounsaturated fatty acid contents, redness and pH of the SWB and MWB samples were higher than the NOR samples. The SWB samples that were stored for 8 d had poor WHC, total viable counts (TVC) of higher than 7.0log colony-forming units, total volatile basic nitrogen (TVB-N) content of greater than 15 mg/100 g and a thiobarbituric acid - reactive substance level of higher than 1 mg/kg malondialdehyde.3. No significant difference was observed in the TVB-N content and TVC of the MWB and NOR samples during storage. Polyunsaturated fatty acid content was lower in the SWB and MWB samples than in the NOR samples. The SWB samples were tougher than the MWB and NOR samples after 8 d of refrigeration.4. In conclusion, the quality of chicken breast meat with SWB myopathy degraded considerably over time; thus, such meat should not be subjected to extended refrigeration for storage.