Comparison of chicken genotypes: myofiber number in pectoralis muscle and myostatin ontogeny

Age-related morphometry, typology and spatial distribution of anterior latissimus dorsi muscle fibre in broiler chicken

The acquisition and processing of muscle tissue images through optical microscopy, along with manual and semi-automatic software techniques, present significant constraints on comprehensive research of a muscle's entire cross-sectional area. To address this limitation, we focused on the anterior latissimus dorsi (ALD) muscle, enabling us to analyse its complete cross-section on a single slide throughout all study stages. This allowed for a detailed assessment, incorporating age-related variations, of histoenzymatic activity across the entire cross-sectional area, along with fibre typology and spatial distribution, and to encourage comparative research across vertebrates to examine species-specific, genetic, ecological and functional influences on histo-enzymomorphometric changes. Leveraging advancements in image acquisition and processing technologies, including slide scanning and automated software, we conducted a comprehensive study on broiler chickens (Gallus gallus Domesticus) at post-hatch ages (D0, D7, D14, D21, D28, D35, D42, D49 and D56), with 10 subjects per age group. The myofibrillar network was visualized using Azorubin staining, while identification of different fibre types in the ALD muscle was achieved through co-revelation of ATPase activity at acidic pH (4.10). Our investigation revealed a progressive decline in the total number of muscle fibres with age. The ALD muscle demonstrated variability in intramuscular distribution, with type IIIa fibres dispersed across the entire muscle surface, showing a consistent increase in percentage with age. Conversely, type IIIb fibres were initially well distributed across the muscle surface during early growth stages but exhibited a gradual decrease with age, particularly in the caudal half of the muscle, reaching minimal values in adulthood. Type IIa fibres were scarce in early ages but appeared in later stages, with percentages not exceeding 5%. The coefficient of variability of type IIa fibres was notably high, indicating the presence of multiple fibre types sharing a common negative reaction to ATPase revelation at acidic pH. This phenomenon suggests a potential conversion of type IIIb fibres into type IIa and IIb fibres. In conclusion, our histoenzymatic study of the entire cross-sectional area of the ALD muscle has provided novel insights into fibre typology and spatial distribution within muscle bundles. Further research to unravel the mechanisms of fibre-type distribution leading to explore the genetic effects of domestication and ecological pressures across species.

Injury and Fibrosis at the Myoaponeurotic Junction of Pectoralis Major and Supracoracoideus Muscles in Broiler Chickens

In this study, we aimed to identify the mechanism responsible for tissue degeneration and fibrosis in pectoral and supracoracoideus muscles. Ten chickens fed ad libitum broiler feed (Bro) were compared to 10 chickens fed breeding feed (Adj), which has lower metabolizable energy. The median body weight of Bro and Adj birds at 48 days of age was 4.9 and 0.9 kg, respectively. In Bro birds, hind legs were farther apart and tended to abduct, whereas their standing posture was often tilted forward, making them unstable. The two Bro males were heavier than the average, markedly less stable when standing or walking, and often flapped their wings vigorously to maintain balance. Myofiber damage and fibrosis were observed at the myoaponeurotic junction of the pectoralis major and supracoracoideus muscles in Bro birds. Myofiber damage and fibrosis were detected also in areas distal to the myoaponeurotic junction in the two heavier males but were otherwise less evident. By contrast, in Adj birds, almost no degeneration or fibrosis of muscle tissue was observed at the myoaponeurotic junction. In addition, the supracoracoideus muscle of one of the Bro birds showed coagulative necrosis of muscle tissue, surrounded by prominent fibrous tissue. Numerous incompletely formed blood vessels with irregular shapes and prominent branching proliferated in the fibrous tissue. These findings suggest that injury at the myoaponeurotic junction and abnormal capillary proliferation may be closely related to the formation of lesions, along with prominent fibrosis in the pectoralis major and supracoracoideus muscles.

Comparative Analysis of Myofiber Characteristics, Shear Force, and Amino Acid Contents in Slow- and Fast-Growing Broilers

Skeletal muscle fiber characteristics are pivotal in assessing meat quality. However, there is currently a lack of research precisely quantifying the total number of myofibers (TNM) of skeletal muscles. This study used Arbor Acres (AA) broilers and Wenchang (WC) chickens to determine the TNM of several skeletal muscles and the meat quality of the pectoralis major muscle (PM). The results showed that the TNMs of the PM in AA males and females were 935,363.64 ± 92,529.28 and 873,983.72 ± 84,511.28, respectively, significantly higher than those in WC (511,468.97 ± 73,460.81 and 475,371.93 ± 70,187.83) at 7 days of age (p < 0.01). In terms of gastrocnemius medialis in AA males and females, we recorded values of 207,551.43 ± 31,639.97 and 177,203.23 ± 28,764.01, showing a significant difference compared to the values observed in WC (146,313.03 ± 29,633.21 and 124,238.9 ± 20,136.95) (p < 0.01). Similarly, the levels of gastrocnemius lateralis exhibited a significant difference between AA and WC (p < 0.01). Furthermore, the essential, umami, and sweet amino acids were found to be significantly higher in WC compared to AA (p < 0.01). These findings offer valuable data and insights for accurately quantifying the TNM in livestock and for the development of further genetic breeding strategies for meat quality.

Transcriptomic analysis reveals differentially expressed genes associated with meat quality in Chinese Dagu chicken and AA+ broiler roosters

BACKGROUND

With the improvement of living standards, the quality of chicken has become a significant concern. Chinese Dagu Chicken (dual-purpose type) and Arbor Acres plus broiler (AA+ broiler) (meat-type) were selected as the research subjects in this study, the meat quality of the breast and leg muscles were measured. However, the molecular mechanism(s) underlying regulation of muscle development are not yet fully elucidated. Therefore, finding molecular markers or major genes that regulate muscle quality has become a crucial breakthrough in chicken breeding. Unraveling the molecular mechanism behind meat traits in chicken and other domestic fowl is facilitated by identifying the key genes associated with these developmental events. Here, a comparative transcriptomic analysis of chicken meat was conducted on breast muscles (BM) and leg muscles (LM) in AA+ broilers (AA) and Dagu chicken (DG) to explore the differences in their meat traits employing RNA-seq.

RESULTS

Twelve cDNA libraries of BM and LM from AA and DG were constructed from four experimental groups, yielding 14,464 genes. Among them, Dagu chicken breast muscles (DGB) vs AA+ broilers breast muscles (AAB) showed 415 upregulated genes and 449 downregulated genes, Dagu chicken leg muscles (DGL) vs AA+ broilers leg muscles (AAL) exhibited 237 upregulated genes and 278 downregulated genes, DGL vs DGB demonstrated 391 upregulated genes and 594 downregulated genes, and AAL vs AAB displayed 122 upregulated genes and 154 downregulated genes. 13 genes, including nine upregulated genes (COX5A, COX7C, NDUFV1, UQCRFS1, UQCR11, BRT-1, FGF14, TMOD1, MYOZ2) and four downregulated genes (MYBPC3, MYO7B, MTMR7, and TNNC1), were found to be associated with the oxidative phosphorylation signaling pathway. Further analysis revealed that the differentially expressed genes (DEGs) from muscle were enriched in various pathways, such as metabolic pathways, oxidative phosphorylation, carbon metabolism, glycolysis, extracellular matrix-receptor interaction, biosynthesis of amino acids, focal adhesion, vascular smooth muscle contraction, and cardiac muscle contraction, all of which are involved in muscle development and metabolism. This study also measured the meat quality of the breast and leg muscles from the two breeds, which demonstrated superior overall meat quality in Chinese Dagu Chicken compared to the AA+ broiler.

CONCLUSIONS

Our findings show that the meat quality of dual-purpose breeds (Chinese Dagu chicken) is higher than meat-type (AA+ broiler), which may be related to the DEGs regulating muscle development and metabolism. Our findings also provide transcriptomic insights for a comparative analysis of molecular mechanisms underlying muscle development between the two breeds, and have practical implications for the improvement of chicken breeding practices.

Transcriptome analysis of long non-coding RNA associated with embryonic muscle development in chickens

1. Skeletal muscle is an important component of chicken carcass. In chickens, the number of muscle fibres is fixed during the embryonic period, and muscle development during the embryonic period determines the muscle development potential after hatching.2. Beijing-You (BY) and Cornish (CN) chickens show completely different growth rates and body types, and two breeds were used in this study to explore the role of lncRNAs in muscle development during different chicken embryonic periods. A systematic analysis of lncRNAs and mRNAs were conducted in the pectoral muscle tissues of BY and CN chickens at embryonic days 11 (ED11), 13 (ED13), 15 (ED15), 17 (ED17), and 1-day-old (D1) using RNA-seq. A total of 4,104 differentially expressed transcripts (DETs) were identified among the five stages, including 2,359 lncRNAs and 1,745 mRNAs.3. The number of DETs between the two breeds at ED17 (1,658 lncRNAs and 1,016 mRNAs) was much higher than the total number of DET at all the other stages (692 lncRNAs and 729 mRNAs), indicating that the two breeds show the largest difference in gene regulation at ED17.4. Correlation analysis was performed for all differentially expressed lncRNAs and mRNAs during the five periods. Forty-three, cis interaction pairs of lncRNA-mRNA related to chicken muscle development were predicted. The expression of four pairs was verified, and the results showed MSTRG.12395.2-FGFBP2 and MSTRG.18590.6-FMOD were significantly up-regulated in CN at ED11 compared to BY and might be important candidate genes for embryonic muscle development.

Myostatin gene role in regulating traits of poultry species for potential industrial applications

The myostatin (MSTN) gene is considered a potential genetic marker to improve economically important traits in livestock, since the discovery of its function using the MSTN knockout mice. The anti-myogenic function of the MSTN gene was further demonstrated in farm animal species with natural or induced mutations. In poultry species, myogenesis in cell culture was regulated by modulation of the MSTN gene. Also, different expression levels of the MSTN gene in poultry models with different muscle mass have been reported, indicating the conserved myogenic function of the MSTN gene between mammalian and avian species. Recent advances of CRISPR/Cas9-mediated genome editing techniques have led to development of genome-edited poultry species targeting the MSTN gene to clearly demonstrate its anti-myogenic function and further investigate other potential functions in poultry species. This review summarizes research conducted to understand the function of the MSTN gene in various poultry models from cells to whole organisms. Furthermore, the genome-edited poultry models targeting the MSTN gene are reviewed to integrate diverse effects of the MSTN gene on different traits of poultry species.

A large-scale comparison of the meat quality characteristics of different chicken breeds in South China

Meat quality traits are essential for producing high-quality broilers, but the genetic improvement has been limited by the complexity of measurement methods and the numerous traits involved. To systematically understand the meat quality characteristics of different broiler breeds, this study collected data on slaughter performance, skin color, fat deposition, and meat quality traits of 434 broilers from 12 different breeds in South China. The results showed that there was no significant difference in the live weight and slaughter weight of various broiler breeds at their respective market ages. Commercial broiler breeds such as Xiaobai and Huangma chickens had higher breast muscle and leg muscle rates. The skin and abdominal fat of Huangma chickens cultivated in the consumer market in South China exhibited significantly higher levels of yellowness compared to other varieties. Concerning fat traits, we observed that Wenchang chickens exhibited a strong ability to fat deposition, while the younger breeds showed lower fat deposition. Additionally, there were significant positive correlations found among different traits, including traits related to weight, traits related to fat, and skin color of different parts. Hierarchical clustering analysis revealed that fast-growing and large broiler Xiaobai chickens formed a distinct cluster based on carcass characteristics, skin color, and meat quality traits. Principal component analysis (PCA) was used to extract multiple principal components as substitutes for complex meat quality indicators, establishing a chicken meat quality evaluation model to differentiate between different breeds of chickens. At the same time, we identified 46, 22, and 20 SNP loci and their adjacent genes that were significantly associated with muscle mass traits, fat deposition, and skin color through genome-wide association studies (GWAS). The above results are helpful for systematically understanding the differences and characteristics of meat quality traits among different breeds.

MyoV: a deep learning-based tool for the automated quantification of muscle fibers

Accurate approaches for quantifying muscle fibers are essential in biomedical research and meat production. In this study, we address the limitations of existing approaches for hematoxylin and eosin-stained muscle fibers by manually and semiautomatically labeling over 660 000 muscle fibers to create a large dataset. Subsequently, an automated image segmentation and quantification tool named MyoV is designed using mask regions with convolutional neural networks and a residual network and feature pyramid network as the backbone network. This design enables the tool to allow muscle fiber processing with different sizes and ages. MyoV, which achieves impressive detection rates of 0.93-0.96 and precision levels of 0.91-0.97, exhibits a superior performance in quantification, surpassing both manual methods and commonly employed algorithms and software, particularly for whole slide images (WSIs). Moreover, MyoV is proven as a powerful and suitable tool for various species with different muscle development, including mice, which are a crucial model for muscle disease diagnosis, and agricultural animals, which are a significant meat source for humans. Finally, we integrate this tool into visualization software with functions, such as segmentation, area determination and automatic labeling, allowing seamless processing for over 400 000 muscle fibers within a WSI, eliminating the model adjustment and providing researchers with an easy-to-use visual interface to browse functional options and realize muscle fiber quantification from WSIs.

Growth of breast muscles in European and Japanese quail raised in meat production system: a morphological analysis

Growth curves have been described in the quail but with no attention to the muscle composing of the breast. The description of the characteristics of growth curves to body weight and to breast muscle was the aim of this study. Morphological development of Musculus supracoracoideus and Musculus pectoralis in European and Japanese quail was assessed from the final incubation of to 35 days. Gompertz models were adjusted with maximum growth rates to body weight, breast weight, and Musculus pectoralis and supracoracoideus weight at 17.6; 22.2; 23.5, and 21.4 days. The European quail had a higher body and breast weight at maturity. Musculus supracoracoideus developed faster in both subspecies but with larger Musculus pectoralis. Both musculus had a greater number of fibers type IIA and largest fibers IIB, with quadratically increasing in fiber diameter with age in both subspecies and muscles. At 35 days, results of meat quality indicated similarity between genders and subspecies, with darker and redness breast meat in Japanese quail. In conclusion, breast weight gain was a result of type IIA and IIB fiber hypertrophy in both muscles and, despite the difference in size and aptitude, Japanese and European quail showed similar body and muscle growth patterns.

Productive performance, breast growth and digestive system development in European quail subjected to post-hatch fasting for different periods

This study assessed the effect of different periods of post-hatch fasting on animal performance and breast and digestive system growth in European quail. Quail chicks were distributed in a completely randomized design, with four fasting periods (0, 24, 36, and 48 hs) and four replications of 40 birds per treatment. In 1 to 14-day-old chicks, weight gain decreased with increasing fasting time. Compensatory gain was observed from 15 days of age onward. Fasted quail had a lower length and relative weight of the digestive system than fed animals for up to 14 days. Histologically, the duodenal villus height was significantly lower in 3-day-old quail fasted for 36 hs than in those fasted for 48 hs, but this effect was not observed at 7 days. Scanning electron microscopy showed no differences in the small intestinal mucosa between fasted and fed birds at 3 days of age. Post-hatch fasting reduced the relative weight of the breast in quail aged 1 to 14 days but did not affect type IIa and IIb fiber diameter at 35 days. On the basis of these results, it is recommended that European quail raised for meat should not be fasted for more than 48 hs post-hatch.

Transcriptomic Analysis on Pectoral Muscle of European Meat Pigeons and Shiqi Pigeons during Embryonic Development

In avian muscle development, embryonic muscle development determines the number of myofibers after birth. Therefore, in this study, we investigated the phenotypic differences and the molecular mechanism of pectoral muscle development of the European meat pigeon Mimas strain (later called European meat pigeon) and Shiqi pigeon on embryonic day 6 (E6), day 10 (E10), day 14 (E14) and day 1 after birth (P1). The results showed that the myofiber density of the Shiqi pigeon was significantly higher than that of the European meat pigeon on E6, and myofibers with a diameter in the range of 50~100 μm of the Shiqi pigeon on P1 were significantly higher than those of European meat pigeon. A total of 204 differential expressed genes (DEGs) were obtained from RNA-seq analysis in comparison between pigeon breeds at the same stage. DEGs related to muscle development were found to significantly enrich the cellular amino acid catabolism, carboxylic acid catabolism, extracellular matrix receptor interaction, REDOX enzyme activity, calcium signaling pathway, ECM receptor interaction, PPAR signaling pathway and other pathways. Using Cytoscape software to create mutual mapping, we identified 33 candidate genes. RT-qPCR was performed to verify the 8 DEGs selected-DES, MYOD, MYF6, PTGS1, MYF5, MYH1, MSTN and PPARG-and the results were consistent with RNA-seq. This study provides basic data for revealing the distinct embryonic development mechanism of pectoral muscle between European meat pigeons and Shiqi pigeons.

Greater numbers and sizes of muscle bundles in the breast and leg muscles of broilers compared to layer chickens

Meat-type (broiler) and egg-type (layer) chickens were bred by intensive selection over the years, resulting in more numbers and larger sizes of myofibers. Although the characteristics are important parameters in muscle growth and meat quality, muscle bundle characteristics have not been studied in poultry. Therefore, this study aimed to compare the histological characteristics of myofibers and muscle bundles in muscles between male broiler (Ross broiler breed) chickens and layer (Hy-Line) chickens. Chicken muscles, pectoralis major (PM) and gastrocnemius (GM), were sampled at the age of 49 days and stained to analyze histological characteristics. Expectedly, body weights (BWs) and weights of PM and GM muscles in 49-day-old broilers were significantly heavier than those in layers. Within PM, broilers exhibited greater number and cross-sectional area (CSA) of myofibers than layers (3.3- and 3.3-fold, respectively). The total number and CSA of PM muscle bundles were approximately 1.5 and 6.6 times greater, respectively, in broilers than layers. Moreover, broilers exhibited 2 times greater number of myofibers per bundle of PM muscle than layers. Within GM, myofiber number and CSA were 2.3- and 2.4-fold greater, respectively, in broilers than layers. In addition, the total number of muscle bundles and bundle CSA were 2.5- and 2.1-fold greater, respectively, in broilers than in the layers. The novel findings of the current study provide evidence that greater muscle mass of broilers occurs by both hyperplasia and hypertrophy of muscle bundles and myofibers.

RNA-Seq-based discovery of genetic variants and allele-specific expression of two layer lines and broiler chicken

Recent advances in the selective breeding of broilers and layers have made poultry production one of the fastest-growing industries. In this study, a transcriptome variant calling approach from RNA-seq data was used to determine population diversity between broilers and layers. In total, 200 individuals were analyzed from three different chicken populations (Lohmann Brown (LB), n = 90), Lohmann Selected Leghorn (LSL, n = 89), and Broiler (BR, n = 21). The raw RNA-sequencing reads were pre-processed, quality control checked, mapped to the reference genome, and made compatible with Genome Analysis ToolKit for variant detection. Subsequently, pairwise fixation index (F ST) analysis was performed between broilers and layers. Numerous candidate genes were identified, that were associated with growth, development, metabolism, immunity, and other economically significant traits. Finally, allele-specific expression (ASE) analysis was performed in the gut mucosa of LB and LSL strains at 10, 16, 24, 30, and 60 weeks of age. At different ages, the two-layer strains showed significantly different allele-specific expressions in the gut mucosa, and changes in allelic imbalance were observed across the entire lifespan. Most ASE genes are involved in energy metabolism, including sirtuin signaling pathways, oxidative phosphorylation, and mitochondrial dysfunction. A high number of ASE genes were found during the peak of laying, which were particularly enriched in cholesterol biosynthesis. These findings indicate that genetic architecture as well as biological processes driving particular demands relate to metabolic and nutritional requirements during the laying period shape allelic heterogeneity. These processes are considerably affected by breeding and management, whereby elucidating allele-specific gene regulation is an essential step towards deciphering the genotype to phenotype map or functional diversity between the chicken populations. Additionally, we observed that several genes showing significant allelic imbalance also colocalized with the top 1% of genes identified by the FST approach, suggesting a fixation of genes in cis-regulatory elements.

Effects of a myostatin mutation in Japanese quail (Coturnix japonica) on the physicochemical and histochemical characteristics of the pectoralis major muscle

The aim of this study was to compare the carcass, meat quality, and histochemical characteristics of pectoralis major (PM) muscle between wild type (WT) and myostatin (Mstn) homozygous mutant (HO) quail lines. The HO quail line exhibited significantly heavier body weight (HO vs. WT, 115.7 g vs. 106.2 g, approximately 110%) and PM muscle weight (HO vs. WT, 18.0 g vs. 15.2 g, approximately 120%) compared to the WT (p &lt; 0.001). However, the two groups had similar traits (pH, redness, yellowness, and drip loss) for meat quality, although slightly higher lightness and cooking loss were observed in the mutant quail (103% and 141%, respectively, p &lt; 0.05). For histochemical traits of PM muscle, Mstn mutant quail exhibited lower type IIA and higher type IIB percentage in the deep region than WT quail (p &lt; 0.05), indicating a fiber conversion from the type IIA to IIB. However, the two quail lines had comparable histochemical traits in the superficial region (p &gt; 0.05). These data suggest that Mstn mutation greatly increases muscle mass without significantly affecting meat quality.

Effect of in ovo creatine monohydrate on hatchability, post-hatch performance, breast muscle yield and fiber size in chicks from young breeder flocks

Younger broiler breeder flocks produce smaller eggs containing smaller yolks, with potentially lower energy reserves for the developing chick. Creatine is a naturally occurring energy source and is abundant in metabolically active tissues; providing this to chicks in ovo should provide additional energy to improve hatchability and post-hatch growth. Thus, post-hatch performance of male and female chicks hatched from younger breeder flocks supplemented with creatine monohydrate (CrM) in ovo was investigated. Four hundred eggs from Ross 308 breeder hens aged 27 to 29 wk were collected and at d 14 assigned to a treatment group and received 1) no injection, 2) 0.75% saline injection, or 3) 8.16 mg creatine monohydrate in 0.75% saline. At hatch 72 birds (24/treatment) were euthanized and BW, breast muscle, heart and liver weight were obtained, and breast muscle tissue was placed in 10% buffered formalin. Birds were then placed in raised metal pens (24 pens; 10-11 birds/pen; 8 replicates/treatment) and grown to d 42 with BW and pen feed intake measured once a week. At d 42, ninty-six birds were euthanized (2 male and 2 female/pen) and the process occurred as at hatch. Body composition was obtained for 48 birds (2/pen; 1 male,1 female) with a dual energy X-ray absorptiometry (DXA) scanner. Breast muscle tissue was processed for histological analysis and breast muscle fiber parameters were analyzed by ImageJ. While not statistically significant, the CrM treatment group saw an improved hatch rate (CrM: 93.5%, Saline: 88.6%, Control: 88.8%) and reduced early post hatch mortality. Chicks given in ovo CrM had significantly increased creatine concentrations in both liver and heart tissue at hatch compared to those in the saline and control groups. BW, BW gain, and final body composition parameters were not statistically different between treatments and in ovo CrM did not affect breast muscle fiber number or area. The creatine injection likely improved the energy status of the growing embryo resulting in the improved hatch rate but leaving little reserves for post-hatch growth.

Research Note: Growth promoting potential in Mstn mutant quail dependent and independent of increased egg size

In avian species, positive relationships between egg weight (EW) and body weight (BW) have been reported. However, the correlation between the body growth rate and different weights of eggs from genetically mutated avian species was not studied yet. Myostatin (Mstn), an anti-myogenic factor, mutant quail were recently developed, and it was reported that EW produced from Mstn homozygous mutant quail (HO) was heavier compared to those from wild-type quail (WT). In the current study, distributions of pre-incubated EW and associations between EW and BW were compared between the Mstn mutant and WT quail lines. Average egg weight for the HO group was significantly heavier than the WT (P < 0.001) and the number of eggs having heavier EW (over 11 g) was higher in the HO compared to the WT (P < 0.01). BWs at wk (W) 0, 4, and 6 after hatch were also significantly greater in the HO (P < 0.001 in all groups). In addition, linear regression analyses revealed positive relationships between EW and BW from W0 to W6, regardless of sexes and genotypes. Furthermore, Mstn mutant quail were a heavier BW compared to the WT quail originated from eggs with similar weights. These data indicate that increased BW by Mstn mutation is contributed by increased EW and/or growth promoting activity of Mstn mutation independent of increasing egg sizes. These findings provide Mstn as a desirable genetic factor for selection of poultry breeds with superior growth. In addition, the knowledge gained from this study could inspire similar proof-of-concept studies involving standard and commercial lines of poultry.

Standardized ileal digestible lysine requirements based on growth performance and histochemical characteristics of male broilers from 10 to 21 d of age

The growth performance and histochemical characteristics of breast muscle fibers were used to estimate the standardized ileal digestible (SID) Lys requirements for 10- to 21-d-old male broilers. Three hundred and sixty 10-d-old Ross 308 broilers (290 ± 16.6 g) were allocated to 6 diets in a randomized complete block design with 6 replicate cages per treatment and 10 birds per cage. The 6 experimental diets were formulated to contain equally spaced increasing levels of SID Lys from 0.86% to 1.36%. The data were analyzed using the MIXED procedure of SAS. The Lys requirements were estimated by the NLIN procedure of SAS. An increase in dietary SID Lys from 0.86% to 1.36% resulted in a quadratic increase (P < 0.05) in body weight gain (BWG), gain to feed ratio (G:F), breast weight, muscle cross-sectional area (MCSA), and fiber area. The SID Lys requirements based on the one-slope broken-line, quadratic line, the first intercept between the plateau of the one-slope broken-line and quadratic-line models and 95% of the upper asymptote of the quadratic-line model were estimated to be 1.01%, 1.19%, 1.08%, and 1.13% for BWG, 1.06%, 1.22%, 1.11%, and 1.16% for G:F, 1.10%, 1.29%, 1.19%, and 1.22% for breast weight, 1.06%, 1.22%, 1.12%, and 1.16% for MCSA, and 1.14%, 1.22%, 1.16%, and 1.16% for breast muscle fiber area, respectively. It was concluded that the SID Lys requirements for broilers at the age of 10 to 21 d depended on the response variables used for estimation, and that histochemical characteristics of breast muscle fibers could be good indicators for estimating SID Lys requirements.

Differential Expression of MSTN Isoforms in Muscle between Broiler and Layer Chickens

Myostatin (Mstn)-A, the main isoform among Mstn splicing variants, functions as a negative regulator, whereas Mstn-B functions as a positive regulator in muscle development. Because broiler chickens are a fast-growing breed raised for meat production and layer chickens are a slow-growing breed raised for egg production, differences in the expression of Mstn isoforms between the two distinct breeds were analyzed in this study. There was no difference in the expression levels of total Mstn (Mstn-A and -B forms) during embryonic development and at D33 between the two breeds. Interestingly, the ratios of Mstn-B to -A were significantly higher in the broiler compared to the layer at most ages. In pectoralis major muscle (PM) tissue, the cross-sectional area (CSA) of muscle fiber was significantly greater in the broiler. The broiler also showed greater bundle CSA and a similar fiber number per bundle compared to the layer at D5 and D33. These data suggest that the greater bundle CSA with myofiber hypertrophy in the broilers is associated with greater muscle growth. The relationship between the expression of Mstn isoforms and growth rate can be used as a potential genetic marker for the selection of higher muscle growth in chickens.

circTAF8 Regulates Myoblast Development and Associated Carcass Traits in Chicken

Recent studies have shown that circular RNAs (circRNAs) play important roles in skeletal muscle development. CircRNA biogenesis is dependent on the genetic context. Single-nucleotide polymorphisms in the introns flanking circRNAs may be intermediate-inducible factors between circRNA expression and phenotypic traits. Our previous study showed that circTAF8 is an abundantly and differentially expressed circRNA in leg muscle during chicken embryonic development. Here, we aimed to investigate circTAF8 function in muscle development and the association of the SNPs in the circTAF8 flanking introns with carcass traits. In this study, we observed that overexpression of circTAF8 could promote the proliferation of chicken primary myoblasts and inhibit their differentiation. In addition, the SNPs in the introns flanking the circTAF8 locus and those associated with chicken carcass traits were analyzed in 335 partridge chickens. A total of eight SNPs were found associated with carcass traits such as leg muscle weight, live weight, and half and full-bore weight. The association analysis results of haplotype combinations were consistent with the association analysis of a single SNP. These results suggest that circTAF8 plays a regulatory role in muscle development. These identified SNPs were found correlated with traits to muscle development and carcass muscle weight in chickens.

Comparison of muscle fiber characteristics and glycolytic potential between slow- and fast-growing broilers

Muscle fiber characteristics had beneficial effects on meat masses and meat quality in broilers. Its number is determined at birth and directly affects the growth and development of muscle fibers after birth. However, whether the muscle fiber characteristics in different types of chickens are different at birth has not been fully documented. In this study, the 1-day-old Xueshan chicken (slow-growing broiler) and Ross 308 broiler (fast-growing broiler) were selected, respectively, and the fiber type distribution, fiber density, and fiber size in the breast (pectoralis major, PM) and leg (gastrocnemius, GAS) muscles were detected. The results showed that the PM only made up of type IIB fibers regardless of breed, and that few type I fibers (approximately 17.55%) was identified in GAS of Ross 308 broiler. The PM muscles had significantly higher fiber density, lower cross-sectional area and diameter than those of GAS muscles in both 2 breeds (P < 0.05). The highest fiber density was observed in PM of Xueshan chicken. Furthermore, the muscle fiber characteristics were partly controlled by glycolytic potential (GP), and the GP was also invesgated. The GP in PM and GAS of Ross 308 broiler were higher than in Xueshan chicken (P < 0.05). Taken together, 1-day-old Xueshan chicken exhibited higher fiber density and lower GP compared to 1-day-old Ross 308 broiler, especially in PM, which could not only reveal the differences of muscle characteristics among different types of chickens, but also explore a new way to improve the masses and quality of poultry meat.

Effect of Muscle Extract and Graphene Oxide on Muscle Structure of Chicken Embryos

Simple Summary

Genetic selection of broilers increased muscle growth; however, very fast growth can lead to pathological conditions caused by the deficiency of nutrients. The number of muscle cells is mainly formed during the embryonic period, and consequently, in ovo supplementation of proteins to embryos may impact future muscle structure. We hypothesized that proteins from chicken embryo muscle extract (CEME) caused by the unique, natural composition and biocompatibility can supply additional proteins. However, supplemented proteins are actively metabolized, which may reduce their utilization for improved muscle synthesis. Nevertheless, CEME can be transported and protected by graphene oxide (GO). The objective of the present work was to investigate the effects of in ovo-injected CEME and the complex of GO-CEME on embryonic cell cultures and the growth of chicken embryo hind limb muscle. Toxicity and cell proliferation were measured in vitro with cell cultures and mortality, morphology, histology, and blood biochemistry in vivo with embryos. CEME increased the number of cells and nuclei in muscle, but the complex GO-CEME did not further improve the muscle structure. The results indicate a vital role of CEME as in ovo enhancer of muscle development in broilers.

Abstract

The effects of CEME and it complex with GO injected in ovo on the growth and development of chicken embryo hindlimb muscle were investigated. First, the preliminary in vitro study on primary muscle precursor cell culture obtained from a nine-day-old chicken embryo was performed to assess toxicity (MTT assay) of CEME, GO (100 ppm) and it complex with different concentrations (1, 2, 5, and 10 wt.%). The effect on cell proliferation was investigated by BrdU assay. CEME at concentrations 1–5% increased cell proliferation, but not the complex with GO. In vitro cytotoxicity was highest in 10% and GO groups. Next, the main experiment with chicken embryos was performed with CEME, GO and it complex injected in ovo on day one of embryogenesis. On day 20 of embryogenesis survival, morphological development, histological structure of the muscle, and biochemical parameters of blood serum of the embryos were measured. No negative effect on mortality, body weight, or biochemistry of blood after use of CEME or GO-CEME complexes was observed. Interestingly, the slight toxicity of GO, observed in in vitro studies, was not observed in vivo. The use of CEME at the levels of 2% and 5% improved the structure of the lower limb muscle by increasing the number of cells, and the administration of 2% CEME increased the number of nuclei visible in the stained cross-section of the muscle. The complex GO-CEME did not further improve the muscle structure. The results indicate that CEME can be applied as an in ovo enhancer of muscle development in broilers.

Research Note: Expression level of heat shock protein 27 in PSE-like and fast-glycolyzing conditions of chicken pectoralis major muscle

This study compared the meat quality traits, histochemical characteristics, and heat shock protein (HSP) 27 expression levels of the broiler Pectoralis major (PM) muscles in groups classified by pale, soft, and exudative (PSE)-like and fast-glycolyzing conditions using the lightness and muscle pH change values. Chicken PM muscles showing higher pH change value and paler meat surface (as HP group) could be associated with the PSE-like condition, and exhibited a lower pH_{24 h} value and higher cooking loss compared to PM muscles showing lower pH change value and normal color (as LN group) (P < 0.05). Greater PM muscle weight and fiber area were observed in the HP group compared to the other groups (P < 0.05); meanwhile, the PM muscles showing higher pH change value with normal color (as HN group) and the PM muscles showing lower pH change value with paler color (as LP group) did not differ in the water holding capacity, Warner-Bratzler shear force, and muscle fiber characteristics (P > 0.05). Muscle samples showing a higher pH change value exhibited a greater level of HSP27 compared to muscle samples showing a lower pH change value (P < 0.05). Therefore, the current findings suggested that the expression level of HSP27 can be a useful indicator for explaining variations in the glycolytic rate of chicken breast muscle.

Myogenetic oligodeoxynucleotide complexed with berberine promotes differentiation of chicken myoblasts

Myoblasts are myogenic precursors that develop into myotubes during muscle formation. Improving efficiency of myoblast differentiation is important for advancing meat production by domestic animals. We recently identified novel oligodeoxynucleotides (ODNs) termed myogenetic ODNs (myoDNs) that promote the differentiation of mammalian myoblasts. An isoquinoline alkaloid, berberine, forms a complex with one of the myoDNs, iSN04, and enhances its activities. This study investigated the effects of myoDNs on chicken myoblasts to elucidate their species-specific actions. Seven myoDNs (iSN01-iSN07) were found to facilitate the differentiation of chicken myoblasts into myosin heavy chain (MHC)-positive myotubes. The iSN04-berberine complex exhibited a higher myogenetic activity than iSN04 alone, which was shown to enhance the differentiation of myoblasts into myotubes and the upregulation of myogenic gene expression (MyoD, myogenin, MHC, and myomaker). These data indicate that myoDNs promoting chicken myoblast differentiation may be used as potential feed additives in broiler diets.

Research Note: Comparison of histochemical characteristics, chicken meat quality, and heat shock protein expressions between PSE-like condition and white-stripping features of pectoralis major muscle

The present study compared the histochemical and meat quality characteristics of broiler pectoralis major (PM) muscle among the groups categorized according to muscle abnormalities, including pale, soft, and exudative (PSE)-like condition and white-striping (WS) feature. Additionally, this study investigated the associations between muscular abnormalities and expression levels of heat shock proteins (HSPs), including αβ-crystallin, HSP70, and HSP90, at the early postmortem period. The WS breasts with normal quality condition showed greater PM muscle weight and were more associated with fiber hypertrophy, compared to the no WS breasts with PSE-like condition (P < 0.05). The PSE-like group exhibited paler surface color and tougher meat, causing more fluid loss after cooking, compared to the normal quality group (P < 0.05). However, there were no significant differences in the quality traits between the WS groups (P > 0.05), except for lightness and cooking loss. Higher αβ-crystallin and HSP90 expression levels were observed in PSE-like breast compared to normal quality breast (P < 0.05), whereas WS pattern was not related with HSPs levels (P > 0.05). Therefore, HSP levels at the early postmortem period, especially those of αβ-crystallin and HSP90, were associated with the breast quality characteristics of PSE-like condition broilers.

Muscle fiber and fresh meat characteristics of white-striping chicken breasts, and its effects on palatability of sous-vide cooked meat

The aim of this study was to compare the histochemical and meat quality characteristics between the normal and white-striping (WS) pectoralis major muscles. Additionally, this study investigated the effects of oven cooking (OV) and sous-vide (SV) cooking methods on objective texture parameters and sensory quality characteristics of the normal and WS chicken breast meats. Results showed that the WS condition broilers had higher body and breast weights (P < 0.001), and a greater area of muscle fiber than the normal broilers (P < 0.001). The WS fresh fillets exhibited a lower preference of visual appearance compared to the normal fillets (P < 0.05), although no differences were detected in the characteristics of meat quality between the groups (P > 0.05). After cooking, there was greater cooking loss, Warner-Bratzler shear force, and texture parameter analysis-hardness values for breast fillets cooked by OV treatment at 180°C for reached core temperature to 71°C compared to the fillets cooked by SV treatment at 60°C for 2 h (P < 0.05), whereas the normal and WS groups were exhibited similar values within each cooking methods (P > 0.05). Regarding sensory quality characteristics, WS breast fillets cooked by SV (SV+WS) were rated as tenderer and juicier, and given a higher overall acceptability score compared to normal and WS fillets cooked by OV (P < 0.05). However, owing to a lesser developed flavor in SV+WS fillets, the panelists assigned a lower overall acceptability rating in these fillets compared to SV+Normal fillets (P < 0.05). Overall, the SV cooking can be an effective method for improving the sensory quality characteristics of WS and normal chicken breast.

Transcription of Endogenous Retrovirus Group K Members and Their Neighboring Genes in Chicken Skeletal Muscle Myoblasts

Skeletal muscle myoblasts are myogenic precursor cells that generate myofibers during muscle development and growth. We recently reported that broiler myoblasts, compared to layer myoblasts, proliferate and differentiate more actively and promptly into myocytes, which corresponds well with the muscle phenotype of broilers. Furthermore, RNA sequencing (RNA-seq) revealed that numerous genes are differentially expressed between layer and broiler myoblasts during myogenic differentiation. Based on the RNA-seq data, we herein report that chicken myoblasts transcribe endogenous retrovirus group K member (ERVK) genes. In total, 16 ERVKs were highly expressed in layer myoblasts and two (termed BrK1 and BrK2) were significantly induced in broiler myoblasts. These transcribed ERVKs had a total of 182 neighboring genes within ±100 kb on the chromosomes, of which 40% were concentrated within ±10 kb of the ERVKs. We further investigated whether the transcription of ERVKs affects the expression of their neighboring genes. BrK1 had two neighboring genes; LOC107052719 was overlapping with BrK1 and downregulated in the broiler myoblasts, and FAM19A2 was upregulated in the broiler myoblasts as well as BrK1. BrK2 had 14 neighboring genes, and only one gene, LOC772243, was differentially expressed between layer and broiler myoblasts. LOC772243 was overlapping with BrK2 and suppressed in the broiler myoblasts. These data indicate that the transcription of ERVKs may impact the expression of their neighboring genes in chicken myoblasts.

Fiber Metabolism, Procollagen and Collagen Type III Immunoreactivity in Broiler Pectoralis Major Affected by Muscle Abnormalities

The present study aimed to evaluate the muscle fiber metabolism and assess the presence and distribution of both procollagen and collagen type III in pectoralis major muscles affected by white striping (WS), wooden breast (WB), and spaghetti meat (SM), as well as in those with macroscopically normal appearance (NORM). For this purpose, 20 pectoralis major muscles (five per group) were selected from the same flock of fast-growing broilers (Ross 308, males, 45-days-old, 3.0 kg live weight) and were used for histochemical (nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) and alpha-glycerophosphate dehydrogenase (α-GPD)) and immunohistochemical (procollagen and collagen type III) analyses. When compared to NORM, we found an increased proportion (p < 0.001) of fibers positively stained to NADH-TR in myopathic muscles along with a relevant decrease (p < 0.001) in the percentage of those exhibiting a positive reaction to α-GPD. In addition, an increased proportion of fibers exhibiting a positive reaction to both stainings was observed in SM, in comparison with NORM (14.3 vs. 7.2%; p < 0.001). After reacting to NADH-TR, SM exhibited the lowest (p < 0.001) cross-sectional area (CSA) of the fibers (-12% with respect to NORM). On the other hand, after reacting to α-GPD, the CSA of WS was found to be significantly larger (+10%) in comparison with NORM (7480 vs. 6776 µm2; p < 0.05). A profound modification of the connective tissue architecture involving a different presence and distribution of procollagen and collagen type III was observed. Intriguingly, an altered metabolism and differences in the presence and distribution of procollagen and collagen type III were even observed in pectoralis major muscle classified as NORM.

Energy metabolism and sources of oxidative stress in wooden breast - a review

Modern broilers show dramatic growth over a short interval and contribute directly to the success of the poultry meat industry. The growth performance of commercial broilers is a result of genetic selection for "performance traits", such as body size, meat yield, and feed conversion rate. However, due to the rapid growth rate of modern commercial broilers, several growth-related conditions have arisen, increasing economic losses and consumer concerns. Among the most economically consequential is the muscle disorder called wooden breast. Together with associated myopathies such as white striping and spaghetti meat, wooden breast is causing losses of $200 million a year in the U.S. alone and occurs worldwide. No causative factors are known for wooden breast to date. Wooden breast can affect over 80% of broilers in a flock, yet no methods of amelioration are currently available. Overall, the evidence suggests that wooden breast is a genetic, age-dependent condition associated with fast growth rate. The primary features of wooden breast are muscle degeneration and fibrosis, high levels of oxidative stress, hypoxia, and altered energy metabolism. Recent work has also implicated reduced pectoral vessel density in the pathogenesis of wooden breast. This review examines the history of myopathies in commercial broilers and the relationship of myopathies to metabolism and oxidative performance. This review summarizes the foundational knowledge of wooden breast and provides a platform for further investigation of wooden breast.

Altered Sarcomeric Structure and Function in Woody Breast Myopathy of Avian Pectoralis Major Muscle

The "Woody" or "Wooden" breast disease is a severe myopathy of pectoralis major muscle recently identified within rapidly growing broiler lines all around the world with a prevalence rate around 20%, or even higher. Although of significant ethical and economic impact, little is known regarding the structural and functional aspects of the contractile apparatus in the woody breast muscle. The aim of the present study was to determine physiological properties of the contractile system in the morphologically intact muscle fibers of focally damaged woody breast in comparison with normal muscle fibers to gain insight into the muscle function of the animal and possibly mechanisms involved in the disease development. Muscle samples were taken from woody breast (non-lesioned areas) and normal breast muscles from broilers. Length-tension curves, maximal active stress, maximal shortening velocity, calcium sensitivity, rate of tension development, lattice spacing and muscle biochemical composition were investigated on single skinned fibers. Sarcomeres of woody breast fibers were more compliant, which is very likely related to the wider spacing (18% wider compared to controls) between thick and thin filament. No differences were found in optimal sarcomere length (2.68 ± 0.04 vs. 2.65 ± 0.05 μm) nor in maximal active stress (116 ± 17 vs. 125 ± 19 mN mm-2). However, woody breast fibers had less steep descending arm as shown in length-tension curve. Woody breast muscle fibers had 40% bigger sarcomeric volume compared to controls. Content of contractile proteins (myosin and actin), and maximal shortening velocity were unchanged indicating that the growth in woody breast muscle fiber was associated with synthesis of new contractile units with unaltered kinetics. Calcium sensitivity was decreased in woody breast muscle fibers significantly. In conclusion, the results show that the rapid growth of muscle in woody breast disease is associated with significant structural and functional changes in the pectoralis major musculature, associated with alterations in the mechanical anchoring of contractile filaments.

Blood Gas Disturbances and Disproportionate Body Weight Distribution in Broilers With Wooden Breast

Wooden breast syndrome is a widespread and economically important myopathy and vasculopathy of fast growing, commercial broiler chickens, primarily affecting birds with high feed efficiency and large breast muscle yield. To investigate potential systemic physiological differences between birds affected and unaffected by wooden breast, a total of 103 market-age Cobb 500 broilers were sampled for 13 blood parameters and the relative weights of the pectoralis major muscle, pectoralis minor muscle, external oblique muscle, wing, heart, lungs, liver, and spleen. Blood analysis was performed on samples taken from the brachial vein of live birds and revealed significant differences in venous blood gases between affected and unaffected chickens. Chickens with wooden breast exhibited significantly higher potassium (K⁺) and lower partial pressure of oxygen (pO₂), oxygen saturation (sO2), and pH. Additionally, affected males had significantly higher partial pressure of carbon dioxide (pCO₂) and total carbon dioxide (TCO₂) than unaffected males. Wooden breast affected broilers also possessed a significantly heavier pectoralis major muscle and whole feathered wing compared to unaffected broilers. Blood gas disturbances characterized by high pCO₂ and low pH are indicative of insufficient respiratory gas exchange, suggesting that wooden breast affected broilers have an elevated metabolic rate that may also be inadequately compensated due to cardiovascular deficiencies such as poor venous return or respiratory insufficiency. Lung tissues from 12 birds with extreme sO₂ values were subsequently examined to assess whether lung pathology contributed to the observed blood gas disturbance. Comparison of lung morphology between affected and unaffected birds revealed no apparent differences that could contribute to decreased parabronchial gas exchange. However, an interesting finding was the detection of pulmonary phlebitis in one of the wooden breast-affected samples consistent with vascular changes observed in pectoralis major muscle exhibiting the wooden breast phenotype. Our results suggest that the effects of wooden breast are not limited to the pectoralis major muscle and further indicate the importance of research into metabolic changes associated with the myopathy.

Effects of in ovo injection of prebiotics and synbiotics on the productive performance and microstructural features of the superficial pectoral muscle in broiler chickens

The aim of the study was to compare the effects of 2 prebiotics and 2 synbiotics injected in ovo on productivity parameters, quality, and microstructure of the superficial pectoral muscle in 35-day-old broiler chickens. On day 12 of incubation, 9,000 eggs Ross 308 were randomly divided into 5 experimental groups treated with different bioactives in ovo injected: C, control with physiological saline; PI, with 1.760 mg inulin; PB, with 0.528 mg of commercial prebiotic Bi2tos; SI, with 1.760 mg inulin and 1,000 CFU Lactococcus lactis spp. lactis IBB SL1; SB, with 0.528 mg Bi2tos and 1,000 CFU Lactococcus lactis spp. cremoris IBB SC1. The synbiotic solution contained 20 μl bacterial suspension and 180 μl prebiotic solution. For productive parameters and further tests ten male birds for each experimental group were used. The birds were slaughtered on day 35 of age. At slaughter, samples of the left pectoral muscles were taken and preserved by freezing in liquid nitrogen. The pH and color of the meat were evaluated at 45 min and 24 h post-mortem. Water holding capacity (WHC) was measured and expressed as the percentage of free water in meat. Microscopic specimens were analysed using MultiScan software for the measurement of the percentage of oxidative and glycolytic fibres and mean diameter of the muscle fibres. In ovo injection of prebiotics Bi2tos had a positive effect on body weight. In prebiotic group (PI) a negative impact on hatchability was observed. Prebiotics and synbiotics had no influence on the yield of the carcass and pectoral muscle. Bioactive compounds had a significant effect on the quality of meat parameters such as: pH 24 h (PI and PB group), L* 45' (SI and SB group), and WHC (groups PB, SI, and SB). The analysis of the enzymatic profile showed a significant increase in the percentage of glycolytic fibres in the pectoral muscle from chicken treated with a synbiotic with the addition of inulin (group SI).

Distinct cell proliferation, myogenic differentiation, and gene expression in skeletal muscle myoblasts of layer and broiler chickens

Myoblasts play a central role during skeletal muscle formation and growth. Precise understanding of myoblast properties is thus indispensable for meat production. Herein, we report the cellular characteristics and gene expression profiles of primary-cultured myoblasts of layer and broiler chickens. Broiler myoblasts actively proliferated and promptly differentiated into myotubes compared to layer myoblasts, which corresponds well with the muscle phenotype of broilers. Transcriptomes of layer and broiler myoblasts during differentiation were quantified by RNA sequencing. Ontology analyses of the differentially expressed genes (DEGs) provided a series of extracellular proteins as putative markers for characterization of chicken myogenic cells. Another ontology analyses demonstrated that broiler myogenic cells are rich in cell cycle factors and muscle components. Independent of these semantic studies, principal component analysis (PCA) statistically defined two gene sets: one governing myogenic differentiation and the other segregating layers and broilers. Thirteen candidate genes were identified with a combined study of the DEGs and PCA that potentially contribute to proliferation or differentiation of chicken myoblasts. We experimentally proved that one of the candidates, enkephalin, an opioid peptide, suppresses myoblast growth. Our results present a new perspective that the opioids present in feeds may influence muscle development of domestic animals.

Muscle characteristics in chicks challenged with Salmonella Enteritidis and the effect of preventive application of the probiotic Enterococcus faecium

The present study was conducted to assess the effects of the probiotic Enterococcus faecium AL41 (EF) and of the enteric pathogen Salmonella Enteritidis PT4 (SE) on the development of posthatch pectoralis major muscle (PM) of broiler chicks. The four experimental groups were control (CON), EF, SE, and EF+SE (EFSE). EF and SE were given per os from days 1 to 7 and at day 4 posthatch, respectively. Muscle samples from 6 chicks per group were taken at day 8 (D8) and day 11 (D11) to evaluate PM myofiber growth, capillarization, DNA, RNA, and protein content, as well as enzyme activities (isocitrate dehydrogenase, lactate dehydrogenase, creatine kinase). PM growth rate was 7.45 ± 2.7 g/d in non-SE groups (CON, EF) and 5.10 ± 1.82 g/d in SE-infected groups (P < 0.02). Compared with group CON, application of bacteria (groups EF and SE) reduced the fiber cross-sectional area (246 and 262 vs. 347 ± 19 μm2) and the number of myonuclei per fiber (0.66 and 0.64 vs. 0.79 ± 0.03). At D11, hypertrophic myofiber growth normalized in the EF group, but negative effects persisted in SE and EFSE birds contributing to lower daily PM gain. In addition, SE infection strongly disturbed PM capillarization. Negative effects on capillary cross-sectional area and on the area (%) covered by capillaries persisted until D11 in the SE group, whereas pre-feeding of EF restored capillarization in the EFSE group to control levels. We conclude that supplementation of the probiotic bacteria EF AL41 had positive effects on PM capillarization and, thus, on delivery of O2, supply of nutrients, and removal of metabolites. Supplementation of probiotic bacteria might therefore reduce energetic stress and improve muscle health and meat quality during SE infection.

Breast meat quality of chickens with divergent growth rates and its relation to growth curve parameters

Abstract. The effects of the increase of body weight of contemporary broilers during growth on functional meat quality and color characteristics of the chicken breast muscle are controversially debated. Therefore, male chickens (n = 264) of a fast-growing commercial broiler (Ross 308) and two slow-growing experimental meat-type chicken lines were compared at equal age and at similar body weight in order to investigate the effect of growth rate on selected functional breast meat traits and meat color. Additionally, the breast meat characteristics of birds with different growth profiles were compared within lines. When the body weight of commercial broilers reached about 40 to 60 % of their growth potential, they exhibited particularly high ultimate pH values compared with slow-growing lines. The ability of the meat of fast-growing broilers to retain water during cooking was impaired (5 to 16 percentage points increased cooking loss compared to slow-growing lines), which, in contrast to pH, was only marginally affected by body weight and/or age at slaughter. No unfavorable correlations of breast meat quality traits with the growth profile, represented by growth curve parameters derived from the Gompertz–Laird equation, were detected within any of the investigated chicken lines. It is noteworthy that the associations of ultimate pH and cooking loss with maximum growth speed indicate a non-linear relationship. Thus, some of the functional characteristics of breast meat of the fast-growing broiler resembled the white-striping defect described for poultry meat, but the hypothesis that selection on increased growth rates is detrimental for meat quality per se could not be confirmed. In fact, an elevated growth potential in particular, i.e., body weight at maturity, could have some beneficial effects for the water-holding capacity of breast meat, regardless of the genotypic growth rate.

Temperature alterations during embryogenesis have a sex-dependent influence on growth properties and muscle metabolism of day-old chicks and 35-day-old broilers

Broiler eggs were either incubated at 37.8°C during the whole incubation period (control), or at higher (38.8°C, group H) and lower temperatures (36.8°C, group L) from embryonic day (ED) 7 up to ED 10 (ED 7 to 10) or from ED 10 up to ED 13 (ED 10 to 13). Before and after this temperature treatment the eggs were incubated at 37.8°C. The day-old chicks were weighted, sexed and fed up to day 35. On days 1 and 35 samples were taken from the breast and leg muscles for analyzing of the mitochondrial respiratory activity (MRA) and from the breast muscles for analysis of the cross-sectional areas (CSA) and the glycogen phosphorylase (GP), phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome oxidase (COX) activities. Statistical analysis showed that treatment (control, group H, group L), sex and their interaction, but not the treatment period (ED 7 to 10; ED 10 to 13), significantly influenced the results. Group H chicks had lower (P⩽0.05) body and heart weights but higher (P⩽0.05) liver weights, CSA values, leg MRA as well as PFK, LDH, CS, GP and COX activities compared with the group L chicks. The results of the control chicks differ (P⩽0.05) from those of the group H (body, heart weight, COX), the group L chicks (liver weight, PFK, LDH, CS, GP) or the birds of both other groups (CSA). The group H broiler had higher (P⩽0.05) body and leg weights as well as LDH, CS, COX and GP activities than the group L broilers. The BWs and the LDH and GP results of the control broiler differ (P⩽0.05) from those of both other groups or from the results of the group H (CS) and group L broiler (COX). Female broilers had lower (P⩽0.05) body, breast and leg weights, but higher (P⩽0.05) CSA, LDH, CS and GP activities than the male animals. Analysis of treatment×sex interaction showed that group H hens had higher (P⩽0.05) body and breast weights, LDH and GP activities compared with the group L hens, whereas in the male broiler no effect of the interaction could be found, except for the lower (P⩽0.05) CSA values in the group H than group L cocks. The treatment effects are probably due to altered embryonic activity and related molecular mechanisms. The sex-related differences in the broiler indicate that these alterations already occur in the embryos and chicks, but become significant with the sexual dimorphism after hatch.

Influence of temperature and growth selection on turkey pectoralis major muscle satellite cell adipogenic gene expression and lipid accumulation

p. major

Immature poults have an inefficient thermoregulatory system, and therefore extreme ambient temperatures can impact their internal body temperature. Satellite cells, the only posthatch myonuclei source, are multipotential stem cells and sensitive to temperature. Selection for faster-growing, high-yielding birds has altered satellite-cell properties. The objective of the current study was to determine how temperature affects adipogenic properties of satellite cells isolated from the pectoralis major ( ) muscle of Randombred Control line ( ) and F line turkeys selected only for increased 16-wk body weight from the RBC2 line. Satellite cells were cultured at 2°C incremental temperatures between 33 and 43°C and compared to cells cultured at the control temperature of 38°C to ascertain temperature effects on lipid accumulation and expression of adipogenic genes: CCAAT/enhancer-binding protein-β ( ), peroxisome proliferator-activated receptor-γ ( ), and stearoyl-CoA desaturase ( ). During proliferation, the amount of quantifiable lipid in both F and RBC2 satellite cells increased at temperatures above 38°C ( P <  0.01) and decreased at temperatures below 38°C ( P < 0.01). Above 38°C, RBC2 satellite cells had more lipid ( P = 0.02) compared to the F line, whereas there were few differences between lines below 38°C. At 72 h of proliferation, expression of C/EBPβ , PPARγ , and SCD decreased ( P ≤  0.02) as temperatures increased from 33 to 43°C in both cell lines. During differentiation expression of C/EBPβ increased ( P <  0.01) as temperatures increased from 33 to 43°C in both cell lines. In F line satellite cells, PPARγ expression decreased ( P <  0.01) with increasing temperatures during differentiation, whereas there was no linear trend in RBC2 cells. During differentiation expression of SCD increased as temperatures increased ( P <  0.01) in RBC2 cells, and there was no linear trend within the F line. Results from the current study suggest that environmental temperature can affect p. major satellite cellular fate; however, selection for increased body weight had little impact on these cellular responses.

The IGF-1/Akt/S6 pathway and expressions of glycolytic myosin heavy chain isoforms are upregulated in chicken skeletal muscle during the first week after hatching

Skeletal muscle mass is an important trait in the animal industry. We previously reported an age-dependent downregulation of the insulin-like growth factor 1 (IGF-1)/Akt/S6 pathway, major protein synthesis pathway, in chicken breast muscle after 1 week of age, despite a continuous increase of breast muscle weight. Myosin heavy chain (HC), a major protein in muscle fiber, has several isoforms depending on chicken skeletal muscle types. HC I (fast-twitch glycolytic type) is known to be expressed in adult chicken breast muscle. However, little is known about the changes in the expression levels of protein synthesis-related factors and HC isoforms in perihatching chicken muscle. In the present study, protein synthesis-related factors, such as IGF-1 messenger RNA (mRNA) levels, phosphorylation of Akt, and phosphorylated S6 content, increased in an age-dependent manner after post-hatch day (D) 0. The mRNA levels of HC I, III and V (fast-twitch glycolytic type) dramatically increased after D0. The increase ratio of breast muscle weight was approximately 1100% from D0 to D7. To our knowledge, these findings provide the first evidence that upregulation of protein synthesis pathway and transcription of fast twitch glycolytic HC isoforms play critical roles in the increase of chicken breast muscle weight during the first week after hatching.

Gene Expression and Polymorphism of Myostatin Gene and its Association with Growth Traits in Chicken

Myostatin is a member of TGF-β super family and is directly involved in regulation of body growth through limiting muscular growth. A study was carried out in three chicken lines to identify the polymorphism in the coding region of the myostatin gene through SSCP and DNA sequencing. A total of 12 haplotypes were observed in myostatin coding region of chicken. Significant associations between haplogroups with body weight at day 1, 14, 28, and 42 days, and carcass traits at 42 days were observed across the lines. It is concluded that the coding region of myostatin gene was polymorphic, with varied levels of expression among lines and had significant effects on growth traits. The expression of MSTN gene varied during embryonic and post hatch development stage.

Comparison of Muscle Fiber and Meat Quality Characteristics in Different Japanese Quail Lines

The aim of this study was to compare the growth performance, fiber characteristics of the pectoralis major muscle, and meat quality characteristics in the heavy weight (HW) and random bred control (RBC) quail lines and genders. The HW male exhibited more than two times greater body (245.7 vs 96.1 g, p<0.05) and pectoralis major muscle (PMW; 37.1 vs 11.1 g, p<0.05) weights compared to the RBC female. This growth performance in the HW line was associated with a greater muscle fiber area (1,502 vs 663.0 μm², p<0.001) compared to the RBC line. Greater muscle mass of the HW male was accompanied by a higher percentage of type IIB fiber compared to the HW female (64.0% vs 51.0%, p<0.05). However, muscle fiber hyperplasia (increase in fiber number) has had a somewhat limited effect on PMW between the two lines. On the other hand, the HW line harboring a higher proportion of type IIB fiber showed rapid pH decline at the early postmortem period (6.23 vs 6.41, p<0.05) and lighter meat surface (53.5 vs 47.3, p<0.05) compared to the RBC line harboring a lower proportion of type IIB fiber. There were no significant differences observed in the measurement of water-holding capacity including drip loss (2.74% vs 3.07%, p>0.05) and cooking loss (21.9% vs 20.4%, p>0.05) between the HW and RBC lines. Therefore, the HW quail line developed by selection from the RBC quail, was slightly different in the meat quality characteristics compared to the RBC line, and a marked difference was found in growth performance between the two quail lines.

Meat quality and the histological structure of breast and leg muscles in Ayam Cemani chickens, Ayam Cemani × Sussex hybrids and slow-growing Hubbard JA 957 chickens

BACKGROUND

The purpose of this study was to determine the quality of meat and the histological structure of muscles of Ayam Cemani chickens, Ayam Cemani × Sussex hybrids and slow-growing Hubbard JA 957 chickens and to examine whether crossing generally available Sussex chickens with little available Ayam Cemani gives a good quality product of interest to the poultry industry and in food technology.

RESULTS

The size of breast and leg muscle fibers varied among genotypes. The breast and leg muscles of slow-growing Hubbard JA 957 chickens had the largest fiber diameter. The histological and biochemical properties of muscles, including the type, number, proportions, diameter and metabolic profile of fibers, had a significant effect on the pH and water-binding capacity of meat, thus affecting its quality. The muscle fibers of Ayam Cemani chickens were approximately half the size of the muscle fibers of Hubbard JA 957 chickens. Ayam Cemani and Ayam Cemani × Sussex gave a product of as good quality as Hubbard JA 957 chickens.

CONCLUSION

Meat from Ayam Cemani chickens is a rich source of protein and could be highly valued by gourmet consumers, connoisseurs and dieticians for its rarity and originality. The results of this study show that genotype (Ayam Cemani, Ayam Cemani × Sussex, Hubbard JA 957) affected the quality and color of meat and the histological profile of chicken breast and leg muscles.

Cloning, characterization and expression of myostatin (growth differentiating factor-8) gene in broiler and layer chicken (Gallus gallus)

A study was conducted to characterize myostatin gene in broiler and layer chicken and to explore mRNA expression profile in these two varieties of chicken. The myostatin cDNAs of broiler and layer varieties were cloned and sequenced. The total length of the cDNA was 1128 bp. The differences of nucleotides between PB-1 broiler and IWI layer were C > 65 > T, C > 306 > T and C > 1094 > T while those between CB broiler and IWI layer were C > 65 > T, C > 195 > G, G > 234 > A, C > 306 > T, T > 939 > C, C > 961 > T, G > 966T and C > 1094 > T. The amino acid differences of myostatin protein between PB-1 and IWI strains were alanine > 22 > valine and proline > 365 > leucine while those between CB and IWI strains were alanine > 22 > valine, histidine > 321 > tyrosine and proline > 365 > leucine. The phylogenetic study revealed closeness of PB-1 and control broiler forming a cluster, which was also closely related to IWI layer chicken formed a separate cluster. The gene was cloned and expressed in E. coli. The gene expression profile in muscle was different between broiler and layer strains. Between two broiler strains, the pattern of expression was similar. Between IWI layer and either PB-1 or CB broilers, differences in expression was found at different time points, particularly at second, fourth and seventh weeks of age. The myostatin expression was significantly associated with body weights in chicken. It is concluded that myostatin gene sequences varied at nucleotide as well as amino acid level between broiler and layer chicken varieties and the gene also expressed differentially in these two varieties.