Dynamic changes in insulin-like growth factor binding protein expression occur between embryonic and early post-hatch development in broiler chickens.

Somatotropic gene expression has been altered by genetic selection, and developmental changes in insulin-like growth factor (IGF) and IGF binding protein (IGFBP) expression may contribute to rapid growth and muscle accretion in commercial broilers. The objective of this study was to evaluate changes in somatotropic axis activity between embryonic day (e) 12 and post-hatch day (d) 21. Liver and breast muscle (pectoralis major) were collected to measure gene expression, and blood was collected post-hatch to measure circulating IGFs. Liver IGF1 rose rapidly post-hatch and, in muscle, IGF1 exhibited a dynamic expression pattern. Levels decreased from e14 to e20, returned to e14 levels at d3, decreased again at d10, and stayed low thereafter. In both tissues, mRNA levels of several IGFBPs changed between embryogenesis and post-hatch. Liver IGFBP2 increased between e12 and e20, returned to e12 levels on d1, and remained low. Conversely, liver IGFBP4 expression was greater post-hatch than during embryogenesis. Expression of select IGFBPs was depressed in liver during the peri-hatch period. Liver IGFBP1, IGFBP3, IGFBP5, and IGFBP7 mRNA levels all decreased around this time and returned to embryonic levels by d3. In breast muscle, expression of both IGFBP2 and IGFBP4 was reduced after hatch. Circulating insulin-like growth factor IGF1 and IGF2 levels did not change between hatch and d21. These data suggest that post-hatch IGF effects are likely modulated by target tissue IGFR1 and IGFBP expression rather than changes in circulating hormone levels, with promotion or restriction of IGF-receptor binding regulating growth. Downregulation of several IGFBPs synthesized in the liver may facilitate the metabolic transition from utilizing yolk lipids to dietary carbohydrates. Several IGFBPs produced in breast muscle appear to have growth-promotive effects during embryogenesis but restrict growth of this tissue after hatch, as their post-hatch downregulation could facilitate local IGF signaling. These developmental gene expression patterns suggest that somatotropic hormonal signaling regulating growth and muscle accretion might be controlled through differential actions of IGFBPs and provide a basis for future functional studies.

Dynamic alternations of three-dimensional chromatin architecture contribute to phenotypic characteristics of breast muscle in chicken.

Breast muscle growth rate and intramuscular fat (IMF) content show apparent differences between fast-growing broilers and slow-growing indigenous chickens. However, the underlying genetic basis of these phenotypic characteristics remains elusive. In this study, we investigate the dynamic alterations of three-dimensional genome architecture and chromatin accessibility in breast muscle across four key developmental stages from embryo to starter chick in Arbor Acres (AA) broilers and Yufen (YF) indigenous chickens. The limited breed-specifically up-regulated genes (Bup-DEGs) are embedded in breed-specific A compartment, while a majority of the Bup-DEGs involving myogenesis and adipogenesis are regulated by the breed-specific TAD reprogramming. Chromatin loops allow distal accessible regions to interact with myogenic genes, and those loops share an extremely low similarity between chicken with different growth rate. Moreover, AA-specific loop interactions promote the expression of 40 Bup-DEGs, such as IGF1, which contributes to myofiber hypertrophy. YF-specific loop interactions or distal accessible regions lead to increased expression of 5 Bup-DEGs, including PIGO, PEMT, DHCR7, TMEM38B, and DHDH, which contribute to IMF deposition. These results help elucidate the regulation of breast muscle growth and IMF deposition in chickens.

Label-free liquid chromatography-mass spectrometry comparison of the breast muscle proteome profiles in two fast-growing broilers.

Poultry meat-production is increasing worldwide; leading to the selection of chickens for meat-production that show a fast growth. A label-free quantitative proteomic-approach and Western-blot were applied to investigate the dynamics of muscle protein under rapid growth conditions in two common fast-growing broiler genetic-lines (Ross 508 and AZ Extra Heavy Red-chicken). Muscle exudate from chicken Pectoralis major was used as substrate to unveil the proteome of these genetic-lines. Six-hundred forty-five proteins were identified in total from all samples, and after statistical-analysis 172 proteins were found to be differentially-expressed, clearly distinguishing the two chicken genetic-lines. Several of these differentially-expressed proteins were involved with the proteasome and glycolysis/gluconeogenesis-pathways. Changes in meat-quality traits were also observed, which were reflected in the proteomic-profile. Proteins involved in the ubiquitin-proteasome system were associated with the bigger muscle mass of Ross 508, while phosphoglucomutase 1 was associated with a possible higher capability of AZ Extra Heavy Red-chickens to cope with stressors. This pilot proteomic-approach applied on muscle exudate samples provided key evidence about the pathways and processes underlying these two chicken genetic-lines and their meat-quality parameters. We also identified potential biomarkers that could determine the peculiar production potentials (e.g. breast-growth) of these broilers-lines, which arise from differences in their genetic-backgrounds.

Ontogeny of hepatic metabolism in two broiler lines divergently selected for the ultimate pH of the Pectoralis major muscle.

BACKGROUND: Nutrient availability during early stages of development (embryogenesis and the first week post-hatch) can have long-term effects on physiological functions and bird metabolism. The embryo develops in a closed structure and depends entirely on the nutrients and energy available in the egg. The aim of this study was to describe the ontogeny of pathways governing hepatic metabolism that mediates many physiological functions in the pHu + and pHu- chicken lines, which are divergently selected for the ultimate pH of meat, a proxy for muscle glycogen stores, and which differ in the nutrient content and composition of eggs. RESULTS: We identified eight clusters of genes showing a common pattern of expression between embryonic day 12 (E12) and day 8 (D8) post-hatch. These clusters were not representative of a specific metabolic pathway or function. On E12 and E14, the majority of genes differentially expressed between the pHu + and pHu- lines were overexpressed in the pHu + line. Conversely, the majority of genes differentially expressed from E18 were overexpressed in the pHu- line. During the metabolic shift at E18, there was a decrease in the expression of genes linked to several metabolic functions (e.g. protein synthesis, autophagy and mitochondrial activity). At hatching (D0), there were two distinct groups of pHu + chicks based on hierarchical clustering; these groups also differed in liver weight and serum parameters (e.g. triglyceride content and creatine kinase activity). At D0 and D8, there was a sex effect for several metabolic pathways. Metabolism appeared to be more active and oriented towards protein synthesis (RPS6) and fatty acid ß-oxidation (ACAA2, ACOX1) in males than in females. In comparison, the genes overexpressed in females were related to carbohydrate metabolism (SLC2A1, SLC2A12, FoxO1, PHKA2, PHKB, PRKAB2 and GYS2). CONCLUSIONS: Our study provides the first detailed description of the evolution of different hepatic metabolic pathways during the early development of embryos and post-hatching chicks. We found a metabolic orientation for the pHu + line towards proteolysis, glycogen degradation, ATP synthesis and autophagy, likely in response to a higher energy requirement compared with pHu- embryos. The metabolic orientations specific to the pHu + and pHu- lines are established very early, probably in relation with their different genetic background and available nutrients.

MeRIP sequencing reveals the regulation of N6-methyladenosine in muscle development between hypertrophic and leaner broilers.

Meat production performance is the most important economic trait in broilers, and skeletal muscle, as the largest organ in animals, is directly related to meat production during embryonic and postnatal growth and development. N6-Methyladenosine (m6A) is a chemical modification occurs on RNA adenosine that has been reported to participate in a variety of biological processes in all species. However, there are still few reports on the regulatory role of muscle growth and development in poultry after birth. This study aims to reveal the distribution of m6A modification sites in chicken pectoralis major muscle after birth and find out the regulatory relationship between m6A and muscle development. As representatives of leaner (Xinghua chicken [XH]) and hypertrophic (White Recessive Rock chicken [WRR]) broilers, there are significant differences in body weight, muscle fiber diameter, and muscle fiber cross-sectional area between XH and WRR chickens. RNA sequencing detected a total of 397 differentially expressed genes (DEG) in the pectoralis major muscle of XH and WRR chicken, and these DEGs were mainly enriched in catalytic activity and metabolic pathways. MeRIP sequencing results showed that among all 6,476 differentially modified m6A peaks, about 90% peaks (5,823) were differentially down regulated in XH chickens. The joint analysis of the mRNA and MeRIP sequencing data found 145 DEGs with differential m6A peak, ALKBH5 as a m6A demethylase, was also included. The highly expression of ALKBH5 in the muscle tissue of poultry and differential expression between XH and WRR chickens suggest that ALKBH5 may play a crucial role in regulating muscle development. Our results revealed that there were significant differences in growth rate, body weight, muscle fiber diameter, and fiber cross-section area between WRR and XH chicken, as well as significant differences in m6A methylation level and muscle metabolism level.

Breast meat quality in males and females of fast-, medium- and slow-growing chickens fed diets of 2 protein levels.

The aim of this study was to evaluate the effects of genotype, sex, dietary protein level, and their interactions on select carcass characteristics and meat quality of fast- (Ross 308), medium- (Hubbard JA757) and slow-growing (ISA Dual) chickens (n = 2,520). The diet of the low-protein group of chickens had 6% lower CP than the commercial diet fed to the control group. When the chickens reached an average live weight of 2 kg, 10 males and 10 females of each genotype and the diet were selected for slaughter and breast meat-quality analysis. The dressing out and breast percentages were lower in the JA757 (-2.0 and -5.9%, respectively) and ISA Dual chickens (-9.9 and -14.3%, respectively) than those in the Ross 308 chickens. The ISA Dual chickens had higher abdominal fat percentage, higher DM and protein contents and lower ether extract content and shear force value in breast meat than the other genotypes. Significant interaction effects of genotype, sex, and diet were found on the color of breast skin. Among the various combinations of genotype, sex, and diet group, Ross 308 females fed the low-protein diet had the highest redness and yellowness of breast skin, highest pH45 value, and largest fibers, whereas ISA Dual females had the lowest color parameters and pH45 value, and ISA Dual males had the smallest muscle fibers. The low-protein diet was associated with decreased abdominal fat percentage and changes in meat quality parameters, including increased darkness, meat color intensity, drip loss, and muscle fiber area, in all genotypes. The results indicated greater differences in meat quality owing to genotype than to sex or dietary protein level.

Effects of marketable ages on meat quality through fiber characteristics in the goose.

Goose meat is increasingly popular among consumers because of its good quality. The fiber characteristics have been well demonstrated to be key contributing factors of meat quality, and the marketable ages are also closely related to meat quality. However, little is known about the effect of different marketable ages on the quality of goose meat through its fiber characteristics. Here, fiber characteristics of Yangzhou geese of different marketable ages (70, 90, and 120 d) and their effect on meat quality were investigated. The results showed that only fast-twitch fibers were present in breast muscle, irrespective of age, and that few slow-twitch fibers could be identified in leg muscle, especially in gastrocnemius and extensor digitorum longus. Fiber diameter in breast muscle increased rapidly from age 70 d to 90 d, from 19.88 to 26.27 µm, and remained stable for 90 d thereafter. The diameter and cross-sectional area of muscle fiber continue to grow with day increasing in leg muscle. In addition, we measured the proximate composition and physical properties at different ages. Among the 3 marketable ages investigated, the 120-day-old geese had higher intramuscular fat and protein content, as well as lower moisture content, both in breast and leg meat. Greater lightness and pressing loss, with lower redness and shear force, were observed in the breast and leg meat of 70-day-old geese when compared with 90- or 120-day-old geese. Taken together, although older marketable age hardly affected muscle fiber type in geese, it would contribute to larger muscle fiber area, higher intramuscular fat and protein content, as well as redder and chewier meat. As a result, the reasonable marketable age should be taken into account to improve quality in goose meat production, and the marketable age of 90 or 120 d was recommended and it could potentially improve meat quality in goose meat production.

Effects of dietary corticosterone on the central adenosine monophosphate-activated protein kinase (AMPK) signaling pathway in broiler chickens.

Glucocorticoids (GCs) induce the activation of the central adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling pathway in birds. In this study, we aimed to investigate the effects of corticosterone (CORT) supplemented in diet on the central AMPK signaling pathway in broilers. The average daily gain was reduced by CORT treatment, and the average daily feed intake remained unchanged. Plasma glucose, triglyceride, total cholesterol, and CORT contents were increased by CORT administration. In addition, CORT treatment decreased the relative weights of heart, spleen, and bursa and increased the relative weights of liver and abdominal fat. The glycogen contents in the liver and breast muscle were higher in the chicks treated with CORT. CORT treatment upregulated the gene expression of mammalian target of rapamycin, glucocorticoid receptor, AMPKα2, neuropeptide Y(NPY), liver kinase B1 (LKB1), AMPKα1, and fatty acid synthase in the hypothalamus. Moreover, CORT treatment increased the protein levels of acetyl-coenzyme A carboxylase (ACC) phosphorylation and total AMPK and phosphorylated AMPK in the hypothalamus. Hence, CORT administration in the diet activated the LKB1-AMPK-NPY/ACC signaling pathway in the hypothalamus of broiler.

Transcriptome analysis reveals a molecular understanding of nicotinamide and butyrate sodium on meat quality of broilers under high stocking density.

BACKGROUND: In recent years, increased attention has been focused on breast muscle yield and meat quality in poultry production. Supplementation with nicotinamide and butyrate sodium can improve the meat quality of broilers. However, the potential molecular mechanism is not clear yet. This study was designed to investigate the effects of supplementation with a combination of nicotinamide and butyrate sodium on breast muscle transcriptome of broilers under high stocking density. A total of 300 21-d-old Cobb broilers were randomly allocated into 3 groups based on stocking density: low stocking density control group (L; 14 birds/m2), high stocking density control group (H; 18 birds/m2), and high stocking density group provided with a combination of 50 mg/kg nicotinamide and 500 mg/kg butyrate sodium (COMB; 18 birds/m2), raised to 42 days of age. RESULTS: The H group significantly increased cooking losses, pH decline and activity of lactate dehydrogenase in breast muscle when compared with the L group. COMB showed a significant decrease in these indices by comparison with the H group (P < 0.05). The transcriptome results showed that key genes involved in glycolysis, proteolysis and immune stress were up-regulated whereas those relating to muscle development, cell adhesion, cell matrix and collagen were down-regulated in the H group as compared to the L group. In contrast, genes related to muscle development, hyaluronic acid, mitochondrial function, and redox pathways were up-regulated while those associated with inflammatory response, acid metabolism, lipid metabolism, and glycolysis pathway were down-regulated in the COMB group when compared with the H group. CONCLUSIONS: The combination of nicotinamide and butyrate sodium may improve muscle quality by enhancing mitochondrial function and antioxidant capacity, inhibiting inflammatory response and glycolysis, and promoting muscle development and hyaluronic acid synthesis.

Divergent selection for relative breast yield at 4 D posthatch and the effect on embryonic and early posthatch development.

Genetic selections for growth promotion in poultry have been highly successful in improving growth, yield, and feed conversion in the modern broiler. These selections have focused on the use of hypertrophy, the increase of muscle fiber size to improve growth. Muscle growth however is not limited solely to hypertrophy but is largely attributable to both hypertrophy and hyperplasia, the increase in muscle fiber number. As muscle fiber size has been theorized to reach an eventual physiological limit, it was determined to develop a novel method of selection focusing on hyperplasia. Divergent selection for 4-day relative breast yield (BY4) was chosen as it is believed to occur at point at which muscle cell number per gram is maximized and satellite cell activity is higher than later in life. Using a random bred control population, divergent selection was undergone for BY4. The 2 broiler lines divergently selected for BY4 are noted as the high and low BY4 lines, respectively (high 4-day breast yield and low 4-day breast yield). Heritability estimates for selection of 4-day breast percentage in the upward and downward directions were 0.63 and 0.44, respectively. Divergent selection resulted in clear divergence in BY4 and shows promise in utilizing BY4 to promote broiler growth and body composition.

Research Note: Association of temporal expression of myostatin with hypertrophic muscle growth in different Japanese quail lines.

Myostatin (MSTN) negatively regulates in muscle growth and development. Among alternative splicing isoforms of avian MSTN, MSTN-A has antimyogenic activities and MSTN-B functions as a promyogenic factor. In this study, different lines of Japanese quail were used: a random bred control (RBC) and a heavy weight (HW) quail line with muscle hypertrophy. The objectives of the current study are to compare temporal expression of the MSTN isoforms in pectoralis major muscle (PM) between 2 quail lines and to relate MSTN expression with temporal changes in muscle growth and total amounts of DNA in PM. Gains of body weight (BW) and PM weight were greater until posthatch day (D) 28 (P < 0.001), and the fold increases in total DNA contents of PM were greater in the HW line compared with the RBC line during D7 to D28 (P < 0.05). PCR analysis showed that MSTN-A expression was greater at 14 D (E14) of embryonic age (P < 0.01), D7 (P = 0.052), and D14 (P < 0.01) in the RBC line compared with the HW line. At D28 and D75, expression of MSTN-A was greater in the HW line compared with the RBC line (P < 0.05). MSTN-B expression was barely detectable from E14 to D14 and measurable from D28 to D75 in the muscle of both lines. Ratios of the MSTN-B/-A form ranging from 0.15 to 0.29 indicate a minor expression of the B form. Taken together, the lesser expression levels of MSTN-A at E14, D7, and D14 are associated with the fast growth of PM, and greater MSTN-A expression at D28 and D75 are associated with a slowdown of PM growth in the HW line. These data indicate a negative association of MSTN expression with PM growth and provide a scientific basis for potential usage of MSTN expression as a selection marker for greater muscle growth in poultry.

A feed restriction milieu for Pekin meat ducks that may improve gait characteristics but also affects gut leakiness.

In a previous study, we demonstrated that a 15% feed restriction (FR) during the first 2 wk after hatch could improve gait in Pekin meat ducks, but did result in reduced breast mass. We hypothesized that feed restriction after day 5 following muscle satellite cell development would allow the full growth of the breast meat. To accomplish this goal, 300 1-day-old ducklings (Maple Leaf Farms Inc.) were randomly allocated to 1 of the 3 groups (n = 4 pens, 25 ducks per pen): (1) Control group fed to ad libitum; (2) 85% daily feed intake from days 1 to 14 (FR 85% 1-14); 85% daily feed intake from days 5 to 14 (FR 85% 5-14). All ducks were vaccinated with inactivated Salmonella enteritidis on day 14 and boosted on day 26. The FR 85% 5-14 did show similar production standards to controls, and improved gait characteristics (P < 0.05). To determine if the partial feed restriction would have an impact on intestinal epithelial tight junction integrity, we treated ducks on days 7, 14, 21, 28, and 35 with 8.32 mg/kg FITC-d in water per os and blood samples were obtained via the tibial vein 1 h later. Serum samples were analyzed for presence and quantification of FITC-d. Feed restriction elicited a significant increase in FITC-d permeability at all points of evaluation. Anti-S. enteritidis specific IgY responses were assessed by ELISA from serum collected at 14 D, 28 D, and 35 D. Although all ducks showed an increase humoral immune response to the S. enteritidis, both feed restricted groups showed reduced IgY production compared to ad lib controls. Our data suggest that although the FR 5-14 feed restriction paradigm may reduce gait abnormalities without affecting production rates, some challenges exist due to increased gut leakiness or decreased acquired immune activity. Future studies will look at altering the feed restriction milieu to ameliorate these challenges.

Effect of in ovo feeding of ß-hydroxy-ß-methylbutyrate on hatchability, muscle growth and performance in prenatal and posthatch broilers.

BACKGROUND: ß-Hydroxy-ß-methylbutyrate (HMB) is the metabolite of leucine that plays an important role in muscle protein metabolism. The objective of the present study was to determine the effects of in ovo feeding (IOF) of HMB at 7 days of incubation (DOI) via air cell or 18 DOI via amnion on hatchability, muscle growth and performance in prenatal and posthatch broilers. RESULTS: IOF of HMB via air cell at 7 DOI increased hatchability by 4.34% compared with the control (89.67% versus 85.33%). Birds in IOF groups exhibited higher body weight, average daily body weight gain and pectoral muscle percentage. Furthermore, IOF of HMB significantly increased the level of plasma growth hormone, insulin and insulin-like growth factor-1. Chicks hatched from IOF treatment had larger diameters of muscle fiber and higher mitotic activity of satellite cells at early posthatch age. IOF of HMB activated satellite cells by upregulation of mRNA expression of myogenic transcription factors, myogenic differentiation one (MyoD) and myogenin. Chicks hatched from air cell injection group had higher pectoral muscle percentage at 5 d posthatch and greater satellite cell mitotic activity at 7 d posthatch than counterparts from amnion injection group. CONCLUSIONS: IOF of HMB via amnion at 18 DOI or especially via air cell at 7 DOI could be used as an effective approach to enhance hatchability, productive performance and breast muscle yield in broilers. © 2019 Society of Chemical Industry.

Differential expression and co-expression gene network analyses reveal molecular mechanisms and candidate biomarkers involved in breast muscle myopathies in chicken.

The broiler industry is facing an increasing prevalence of breast myopathies, such as white striping (WS) and wooden breast (WB), and the precise aetiology of these occurrences remains poorly understood. To progress our understanding of the structural changes and molecular pathways involved in these myopathies, a transcriptomic analysis was performed using an 8 × 60 K Agilent chicken microarray and histological study. The study used pectoralis major muscles from three groups: slow-growing animals (n = 8), fast-growing animals visually free from defects (n = 8), or severely affected by both WS and WB (n = 8). In addition, a weighted correlation network analysis was performed to investigate the relationship between modules of co-expressed genes and histological traits. Functional analysis suggested that selection for fast growing and breast meat yield has progressively led to conditions favouring metabolic shifts towards alternative catabolic pathways to produce energy, leading to an adaptive response to oxidative stress and the first signs of inflammatory, regeneration and fibrosis processes. All these processes are intensified in muscles affected by severe myopathies, in which new mechanisms related to cellular defences and remodelling seem also activated. Furthermore, our study opens new perspectives for myopathy diagnosis by highlighting fine histological phenotypes and genes whose expression was strongly correlated with defects.

Krüppel-like factor KLF9 inhibits chicken intramuscular preadipocyte differentiation.

1. Poultry meat quality is affected by many factors, among which intramuscular fat (IMF) is predominant. IMF content affects tenderness, juiciness and flavour of meat. Krüppel-like transcriptional factors (KLFs) are important regulators of adipocyte differentiation. However, little is known about the KLF9 gene associated with poultry IMF deposition, especially intramuscular adipocyte differentiation.2. Previous work has shown that chicken KLF9 was differentially expressed during adipogenesis of intramuscular preadipocytes differentiation. In this study, the function of KLF9 in chicken intramuscular preadipocytes differentiation was investigated.3. In the chicken preadipocyte differentiation model, KLF9 expression showed a major increase with adipogenic induction. Overexpression of KLF9 down-regulated the expression of the adipogenic marker gene AP2, and impaired triglyceride accumulation. Knockdown of KLF9 in chicken intramuscular preadipocytes increased the expression of PPARG, CEBPA and AP2. In addition, it was proposed that KLF9 may regulate adipogenesis via lncRNAs NONGGAT002209.2, NONGGAT003346.2, NONGGAT000436.2 and NONGGAT006302.2 in chicken.4. The data supported a novel role of KLF9 in regulating chicken intramuscular preadipocyte differentiation. Such findings may contribute to a more thorough understanding of chicken IMF deposition and the improvement of poultry meat quality.

Expression of MSTN gene and its correlation with pectoralis muscle fiber traits in the domestic pigeons (Columba livia).

Myostatin (MSTN) is a negative regulator of skeletal muscle growth and plays an important role in muscle development. In this research, we constructed a tissue expression profile of the pigeon MSTN gene in eight tissues and a spatio-temporal expression profile in the pectoral muscle using qRT-PCR method. And the pectoralis muscle fiber traits during pigeon post-hatching stages at 1, 7, 14, 21, and 28 D were analyzed through the paraffin sections. Then the correlations between the muscle fiber diameter, cross-sectional area, density, and the expression of MSTN in the pectoral muscle were analyzed. Results showed that MSTN mRNA was mainly expressed in breast muscle, heart, spleen, and kidney and it was almost unexpressed in the liver and lungs. Moreover, the MSTN mRNA expression level in breast muscle was significantly higher than that in other tissues (P < 0.05), and showed an interesting trend that it decreased in the first week and then increased with age. Meanwhile, decrease of myostatin transcripts was accompanied by the down-regulation of Myf5 and the up-regulation of MyoG during the first week post-hatching. In addition, the paraffin sections analysis results revealed that the diameter and cross-sectional area of pectoralis muscle fiber significantly increased with age (P < 0.05), and a significant positive correlation was shown between the MSTN gene expression level and muscle fiber diameter (P < 0.05). These fundamental researches might contribute to further understanding of the roles MSTN played in the post-hatching muscle fiber development in pigeon.

Early posthatch thermal stress causes long-term adverse effects on pectoralis muscle development in broilers.

Broiler chicks in the immediate posthatch handling period are exposed to thermal stress, with potentially harmful consequences for muscle growth and structure (e.g., less protein and more fat deposition). We addressed the effects of broiler chicks' exposure to various ambient temperatures during the first 13 D posthatch on their performance, as well as on muscle development and structure, up to day 35. Body weight and pectoralis muscle growth were lower throughout the entire period in the high-heat-exposed chicks (39°C, Hot) and to a lesser extent in the mild-heat-exposed chicks (35°C, Hot Mild) than in the Control chicks that were raised under a commercial protocol. In the cold-exposed chicks (29oC, Cold), BW and pectoralis muscle absolute growth were similar to the Control group throughout the entire period. The lower body and muscle growth in the Hot and Hot Mild groups were reflected in a lower number of myonuclei expressing proliferating cell nuclear cell in pectoralis major muscle cross sections sampled on day 8, in the distribution of myofibers as the experiment progressed, and in mean myofiber diameter on day 35, whereas in the Cold group, these numbers exceeded that of the Control group. However, TUNEL assay revealed similar cell survival in all groups. Hematoxylin-eosin and Oil red O staining revealed the highest fat deposition in the pectoralis muscle derived from the Hot group, whereas lower fat deposition was observed in the Control Cold group. These results were corroborated by immunostaining for CCAAT/enhancer binding protein ß in the pectoralis muscle, the levels of which were significantly higher in the Hot and Hot Mild groups on day 35 than in the Control group. Similar results were observed with Sirius red staining for collagen content in the pectoralis muscle. Together, the results imply long-term effects of chronic heat stress vs. cold stress in the early posthatch period on the broiler's body and muscle growth in general and myodegeneration of the pectoralis muscle in particular.

The effects of an alternative diet regimen with natural methionine ingredients on white striping breast myopathy in broiler chickens.

Conventional broiler diets include synthetic methionine to optimize fast muscle growth. Recently, a conventional synthetic methionine-rich diet was compared to alternative diet regimens providing natural sources of methionine. Broilers fed diets with natural methionine sources grew at a slightly slower rate. From this study, we hypothesized that the difference in a growth rate would be reflected in features of the breast muscle from broilers fed the alternative diet. We hypothesized that white striping of pectoralis major muscle would be reduced in slower growing broilers fed the alternative diet regimen with natural methionine. We also hypothesized that there would be associated differences in gene expression for cell differentiation and pathology markers. Broilers fed a conventional corn/soy diet regimen with synthetic methionine were compared to those fed roasted cowpea and sunflower seed meal (60% corn/soy, 20% sunflower seed meal, and 20% roasted cowpea) and no synthetic methionine. Overall broiler growth, muscle gene expression, and muscle collagen content data were compared. Expression analyses of combinations of MYOD1, PPARG, COL1A2, TRIM63, SOD1, PTGS2, and CD36 genes were used to examine differentiation and inflammation in the pectoralis muscles. The group fed an alternative diet gained less weight than those fed the control diet in the starter and grower phases but not in the finisher phase. Ultimately, the conventional diet resulted in a greater final weight for the broilers. However, mean white striping scores for the pectoralis major muscles were greater in the conventional control diet regimen. Gene expression results indicated greater expression of PPARG, PTGS2, and CD36 in the muscle of broilers fed the control diet. These data associate white striping with fat deposition and inflammation. Thus, whether due to differences in feed intake, growth rate, or actual compositional differences, the alternative diet with natural methionine sources seemed to curtail amounts of white striping in broiler muscle. More studies are necessary to further discern the effect of growth rate and natural methionine sources on white striping.

Comparative transcriptome analysis reveals regulators mediating breast muscle growth and development in three chicken breeds.

Objective: The goal of this study was to investigate the mechanisms of muscle growth and development of three chicken breeds. Participants: Eighteen chickens, including three different breeds with different growth speeds (White Broiler, Daheng, and Commercial Layers of Roman), were used. Methods: Total RNA from breast muscle of these chickens was subjected to a gene expression microarray. Differentially expressed genes (DEGs) were screened and functional enrichment analysis was performed using DAVID. Seven DEGs were confirmed by quantitative reverse transcription PCR. Results: Overall, 8,398 DEGs were found among the different lines. The DEGs between each two lines that were unique for a developmental stage were greater than those that were common during all stages. Functional analysis revealed that DEGs across the entire developmental process were primarily involved in positive cell proliferation, growth, cell differentiation, and developmental processes. Genes involved in muscle regulation, muscle construction, and muscle cell differentiation were upregulated in the faster-growing breed compared to the slower-growing breed. DEGs including myosin heavy chain 15 (MYH15), myozenin 2 (MYOZ2), myosin-binding protein C (MYBPC3), insulin-like growth factor 2 (IGF2), apoptosis regulator (BCL-2), AP-1 transcription factor subunit (JUN), and AP-1 transcription factor subunit (FOS) directly regulated muscle growth or were in the center of the protein-protein interaction network. Pathways, including the extracellular matrix (ECM)-receptor interaction, mitogen-activated protein kinase (MAPK) signaling pathway, and focal adhesion, were the most enriched DEGs between lines or within lines under different developmental stages. Conclusions: Genes involved in muscle construction and cell differentiation were differentially expressed among the three breeds.

The effect of nutrient restriction on the proliferation and differentiation of turkey pectoralis major satellite cells differing in age and growth rate.

Myogenic satellite cells are critical for posthatch muscle growth, and their activity is sensitive to nutritional regime during the immediate posthatch period. The objective of the current study was to determine if the response of satellite cells to nutrient restriction was dependent on bird age and/or growth rate. Satellite cells were isolated from the pectoralis major (p. major) muscle of 1-d, 7-wk, and 16-wk-old turkeys selected for increased body weight at 16 wk of age (F line) and the randombred control (RBC2) line from which the F line was selected. Nutrient restriction of 0, 5, 10, 20, and 40% of the standard cell culture medium was applied during proliferation with subsequent normal differentiation medium (RN) or during differentiation with preceding normal proliferation medium (NR). Satellite cell proliferation and differentiation decreased with nutrient restriction for all treatment regimens and ages, except for 1-d cell differentiation with the RN treatment, which increased with nutrient restriction. Interestingly, after 24 h of a 5% nutrient restriction during the RN treatment, proliferation increased for 1-d and 7-wk cells. Additionally, after 24 h of 5, 10, and 20% nutrient restriction during the NR treatment, differentiation increased for 1-d and 7-wk cells. The 16-wk cells did not exhibit this response to any treatment regimen. Growth rate had little effect on satellite cell response to nutrient restriction. In this study, satellite cells differentially responded to nutrient restriction depending on age, as well as duration and timing of the nutrient restriction. These data suggest that it is necessary to optimize diets throughout a bird's life to maximize satellite cell activity and p. major muscle growth.