Effect of selection for growth rate on muscle damage during turkey breast muscle development

Towards more realistic cultivated meat by rethinking bioengineering approaches

Cultivated meat (CM) refers to edible lab-grown meat that incorporates cultivated animal cells. It has the potential to address some issues associated with real meat (RM) production, including the ethical and environmental impact of animal farming, and health concerns. Recently, various biomanufacturing methods have been developed to attempt to recreate realistic meat in the laboratory. We therefore overview recent achievements and challenges in the production of CM. We also discuss the issues that need to be addressed and suggest additional recommendations and potential criteria to help to bridge the gap between CM and RM from an engineering standpoint.

Data-Mining Methodology to Improve the Scientific Production Quality in Turkey Meat and Carcass Characterization Studies

The present research aims to describe how turkey meat and carcass quality traits define the interest of the scientific community through the quality standards of journals in which studies are published. To this end, an analysis of 92 research documents addressing the study of turkey carcass and meat quality over the last 57 years was performed. Meat and carcass quality attributes were dependent variables and included traits related to carcass dressing, muscle fiber, pH, colorimetry, water-holding capacity, texture, and chemical composition. The independent variables comprised publication quality traits, including journal indexation, database, journal impact factor (JIF), quartile, publication area, and JIF percentage. For each dependent variable, a data-mining chi-squared automatic interaction detection (CHAID) decision tree was developed. Carcass or piece yield was the only variable that did not show an impact on the publication quality. Moreover, color and pH measurements taken at 72 h postmortem showed a negative impact on publication interest. On the other hand, variables including water-retaining attributes, colorimetry, pH, chemical composition, and shear force traits stood out among the quality-enhancing variables due to their low inclusion in papers, while high standards improved power.

Fatty Acid Profile, Volatile Organic Compound, and Physical Parameter Changes in Chicken Breast Meat Affected by Wooden Breast and White Striping Myopathies

The aim of this research was to determine the impact of pectoralis major myopathies on the physical parameters, fatty acid (FA) profile, and volatile organic compound (VOC) composition of chicken breast meat. Samples were collected from pectoralis major of broilers with varying severity scores (normal, mild, and severe) of wooden breast (WB) and white striping (WS) myopathies. Chicken breast meat affected by severe myopathies expressed higher cooking loss, drip loss (p < 0.001), and yellowness (p < 0.05) compared to those of samples that were taken from broilers without myopathies (normal). The amount of monounsaturated fatty acids (MUFAs) was significantly higher in samples affected by mild and severe myopathies than in those without myopathies (p < 0.05). There was significantly more aldehyde hexanal in muscles affected by mild and severe myopathies than in muscles without myopathies (p < 0.05). In conclusion, WB and WS myopathies of the breast muscle not only affected the physical parameters of broiler meat but also may have influenced its FA profile and VOC composition. Additionally, an elevated amount of hexanal in muscles affected by WB together with WS suggests that oxidative stress could be important in the etiopathogenesis of WB and WS myopathies. Therefore, poultry meat affected by myopathies have the potential to alter breast meat flavor and composition.

Broiler breast muscle myopathies: association with satellite cells

Heavy weight fast-growing meat-type broiler chickens have largely been selected for growth rate, muscle mass yield especially for the breast muscle, and feed conversion. Substantial improvements have been made, but in recent years breast meat quality issues resulting in product downgrades or condemnation have occurred especially from necrotic and fibrotic myopathies like Wooden Breast. In general, the morphological structure of the broiler breast muscle has changed in the modern commercial broiler with muscle fiber diameters increased, circulatory supply decreased, and connective spacing between individual fibers and fiber bundles decreased. Satellite cells are the primary cell type responsible for all posthatch muscle growth, and the repair and regeneration of muscle fibers. Recent evidence is suggestive of changes in the broiler satellite cell populations which will limit the ability of the satellite cells to regenerate damaged muscle fibers back to their original. These changes in the cellular biology of broiler satellite cells are likely associated with the necrosis and fibrosis observed in myopathies like Wooden Breast.

Morphological, radiographic, three-dimensional computed tomographic, and histological features of the primary upstroke and downstroke muscles and bones in the domestic duck (Anas platyrhynchos domesticus) and the cattle egret (Bubulcus ibis, Linnaeus, 1758), reflecting the evolutionary transition towards the irreversible flightlessness

BACKGROUND

The purpose of this study was to explore whether domestication could lead to evolutionary changes towards flightlessness in the domestic duck (Anas platyrhynchos domesticus) compared to the cattle egret (Bubulcus ibis) as a nonflying and flying biological model, respectively. Bones of the pectoral girdle (scapula, clavicle, and coracoid) and the foramen triosseum were comparatively assessed using anatomical, radiographic, and 3D computed tomographic (CT) studies. Additionally, the muscles pectoralis and the supracoracoideus were histologically and immunohistochemically assessed.

RESULTS

Among the differences observed, radiographically, the distance between the paired clavicles was significantly wider (p < 0.05) in the domestic duck (mean ± SD 1.43 ± 0.23 cm) compared with the cattle egret (0.96 ± 0.13 cm). Unlike cattle egrets, there was no connection between the sternum and the hypocladium of furcula in domestic ducks. The scapula, clavicle, coracoid, sternum, and humerus were considerably longer in domestic ducks than in cattle egrets. The foramen triosseum appeared significantly (p < 0.01) wider in domestic ducks (0.7 ± 1.17 cm) compared to cattle egrets (0.49 ± 0.03 cm). Histologically, compared to cattle egrets, the muscle fibers in domestic ducks were loosely connected and contained fewer nuclei and perimysial/endomysial spaces. A higher myoglobin expression was evident in cattle egrets compared with domestic ducks.

CONCLUSIONS

Results of this study indicate that the bones and muscles of the pectoral girdle generally show specific morphological and structural changes reflective of the loss of prerequisites associated with flight behavior in domestic ducks due to domestication effects compared to cattle egrets.

Effects of thermal stress and mechanistic target of rapamycin and wingless-type mouse mammary tumor virus integration site family pathways on the proliferation and differentiation of satellite cells derived from the breast muscle of different chicken lines

Satellite cells (SCs) are muscle stem cells responsible for muscle hypertrophic growth and the regeneration of damaged muscle. Proliferation and differentiation of the pectoralis major (p. major) muscle SCs are responsive to thermal stress in turkeys, which are, in part, regulated by mechanistic target of rapamycin (mTOR) and Frizzled7 (Fzd7)-mediated wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) pathways in a growth dependent-manner. It is not known if chicken p. major SCs respond to thermal stress in a manner similar to that of turkey p. major SCs. The objective of the current study was to investigate the effects of thermal stress and mTOR and Wnt/PCP pathways on the proliferation, differentiation, and expression of myogenic transcriptional regulatory factors in SCs isolated from the p. major muscle of a current modern commercial (MC) broiler line as compared to that of a Cornish Rock (BPM8) and Randombred (RBch) chicken line in the 1990s. The MC line SCs had lower proliferation and differentiation rates and decreased expression of myoblast determination factor 1 (MyoD) and myogenin (MyoG) compared to the BPM8 and RBch lines. Heat stress (43°C) increased proliferation and MyoD expression in all the cell lines, while cold stress (33°C) showed a suppressive effect compared to the control temperature (38°C). Satellite cell differentiation was altered with heat and cold stress in a cell line-specific manner. In general, the differentiation of the MC SCs was less responsive to both heat and cold stress compared to the BPM8 and RBch lines. Knockdown of the expression of either mTOR or Fzd7 decreased the proliferation, differentiation, and the expression of MyoD and MyoG in all the cell lines. The MC line during proliferation was more dependent on the expression of mTOR and Fzd7 than during differentiation. Thus, modern commercial meat-type chickens have decreased myogenic activity and temperature sensitivity of SCs in an mTOR- and Fzd7-dependent manner. The decrease in muscle regeneration will make modern commercial broilers more susceptible to the negative effects of myopathies with muscle fiber necrosis requiring satellite cell-mediated repair.

Differential effects of temperature and mTOR and Wnt-planar cell polarity pathways on syndecan-4 and CD44 expression in growth-selected turkey satellite cell populations

Satellite cells (SCs) comprise a heterogeneous population of muscle stem cells. Thermal stress during the first week after hatch alters proliferation, myogenesis, and adipogenesis of SCs of turkey pectoralis major (p. major) muscle via mechanistic target of rapamycin (mTOR) and wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) pathways. Pivotal genes in mTOR and Wnt/PCP pathways are mTOR and frizzled-7 (Fzd7), respectively. The objective of this study was to determine the differential effects of thermal stress on SDC4 and CD44 expression in turkey p. major muscle SCs and how the expression of SDC4 and CD44 is modulated by the mTOR and Wnt/PCP pathways. Satellite cells were isolated from the p. major muscle of 1-week-old faster-growing modern-commercial (NC) turkeys and slower-growing historic Randombred Control Line 2 (RBC2) turkeys, and were challenged with hot (43°C) and cold (33°C) thermal stress for 72 h of proliferation followed by 48 h of differentiation. The NC line SCs were found to contain a lower proportion of SDC4 positive and CD44 negative (SDC4+CD44-) cells and a greater proportion of SDC4 negative and CD44 positive (SDC4-CD44+) cells compared to the RBC2 line at the control temperature (38°C) at both 72 h of proliferation and 48 h of differentiation. In general, at 72 h of proliferation, the proportion of SDC4+CD44- cells decreased with heat stress (43°C) and increased with cold stress (33°C) relative to the control temperature (38°C) in both lines, whereas the proportion of SDC4-CD44+ cells increased with heat stress and decreased with cold stress. In general, the expression of SDC4 and CD44 in the NC SCs showed greater response to both hot and cold thermal stress compared to the RBC2 cells. Knockdown of mTOR or Fzd7 expression increased the proportion of SDC4+CD44- cells while the proportion of SDC4-CD44+ cells decreased during differentiation with line differences being specific to treatment temperatures. Thus, differential composition of p. major muscle SCs in growth-selected commercial turkey may be resulted, in part, from the alteration in SDC4 and CD44 expression. Results indicate differential temperature sensitivity and mTOR and Wnt/PCP pathway responses of growth-selected SC populations and this may have long-lasting effect on muscle development and growth.

Transcriptome response of proliferating muscle satellite cells to thermal challenge in commercial turkey

Thermal stress poses a threat to agricultural systems through increased risk to animal growth, health, and production. Exposure of poultry, especially hatchlings, to extreme temperatures can seriously affect muscle development and thus compromise subsequent meat quality. This study was designed to characterize transcriptional changes induced in turkey muscle satellite cells (SCs) cultured from commercial birds under thermal challenge to determine the applicability of previous results obtained for select research lines. Satellite cells isolated from the pectoralis major muscle of 1-week old commercial fast-growing birds (Nicholas turkey, NCT) and from a slower-growing research line (RBC2) were proliferated in culture at 38°C or 43°C for 72 h. RNAseq analysis found statistically significant differences in gene expression among treatments and between turkey lines with a greater number of genes altered in the NCT SCs suggesting early myogenesis. Pathway analysis identified cell signaling and regulation of Ca2+ as important responses. Expression of the intercellular signaling Wnt genes, particularly Wnt5a and 7a was significantly altered by temperature with differential response between lines. The peripheral calcium channel RYR3 gene was among the genes most highly upregulated by heat stress. Increased expression of RYR3 would likely result in higher resting cytosolic calcium levels and increased overall gene transcription. Although responses in the calcium signaling pathway were similar among the RBC2 and NCT lines, the magnitude of expression changes was greater in the commercially selected birds. These results provide evidence into how SC activity, cellular fate, and ultimately muscle development are altered by heat stress and commercial selection.

Thermal stress and selection for growth affect myogenic satellite cell lipid accumulation and adipogenic gene expression through mechanistic target of rapamycin pathway

Satellite cells (SCs) are multipotential stem cells having the plasticity to convert to an adipogenic lineage in response to thermal stress during the period of peak mitotic activity (the first week after hatch in poultry). The mechanistic target of rapamycin (mTOR) pathway, which regulates cellular function and fate of SCs, is greatly altered by thermal stress in turkey pectoralis major muscle SCs. The objective of the present study was to determine the effects of thermal stress, selection for growth, and the role of the mTOR pathway on SC intracellular lipid accumulation and expression of adipogenic regulatory genes. These effects were analyzed using SCs isolated from the pectoralis major muscle of 1-wk-old modern faster-growing commercial turkey line (NC) selected for increased growth and breast muscle yield as compared with SCs of a historic slower-growing Randombred Control Line 2 (RBC2) turkey. Heat stress (43 °C) of SCs during proliferation increased intracellular lipid accumulation (P < 0.001), whereas cold stress (33 °C) showed an inhibitory effect (P < 0.001) in both lines. Knockdown of mTOR reduced the intracellular lipid accumulation (P < 0.001) and suppressed the expression of several adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ (PPARγ; P < 0.001), CCAAT/enhancer-binding protein-β (C/EBPβ; P < 0.001), and neuropeptide-Y (NPY; P < 0.001) during both proliferation and differentiation. The NC line SCs showed fewer reductions in lipid accumulation compared with the RBC2 line independent of temperature. Both intracellular lipid accumulation (P < 0.001) and PPARγ expression (P < 0.001) were greater at 72 h of proliferation than at 48 h of differentiation in both the RBC2 and NC lines independent of temperature. Thus, hot and cold thermal stress affected intracellular lipid accumulation in the pectoralis major muscle SCs, in part, through the mTOR pathway in wea growth-dependent manner. Altered intracellular lipid accumulation could eventually affect intramuscular fat deposition, resulting in a long-lasting effect on the structure and protein to fat ratio of the poultry pectoralis major muscle.

Skeletal muscle and metabolic flexibility in response to changing energy demands in wild birds

Phenotypically plastic responses of animals to adjust to environmental variation are pervasive. Reversible plasticity (i.e., phenotypic flexibility), where adult phenotypes can be reversibly altered according to prevailing environmental conditions, allow for better matching of phenotypes to the environment and can generate fitness benefits but may also be associated with costs that trade-off with capacity for flexibility. Here, we review the literature on avian metabolic and muscle plasticity in response to season, temperature, migration and experimental manipulation of flight costs, and employ an integrative approach to explore the phenotypic flexibility of metabolic rates and skeletal muscle in wild birds. Basal (minimum maintenance metabolic rate) and summit (maximum cold-induced metabolic rate) metabolic rates are flexible traits in birds, typically increasing with increasing energy demands. Because skeletal muscles are important for energy use at the organismal level, especially to maximum rates of energy use during exercise or shivering thermogenesis, we consider flexibility of skeletal muscle at the tissue and ultrastructural levels in response to variations in the thermal environment and in workloads due to flight exercise. We also examine two major muscle remodeling regulatory pathways: myostatin and insulin-like growth factor -1 (IGF-1). Changes in myostatin and IGF-1 pathways are sometimes, but not always, regulated in a manner consistent with metabolic rate and muscle mass flexibility in response to changing energy demands in wild birds, but few studies have examined such variation so additional study is needed to fully understand roles for these pathways in regulating metabolic flexibility in birds. Muscle ultrastrutural variation in terms of muscle fiber diameter and associated myonuclear domain (MND) in birds is plastic and highly responsive to thermal variation and increases in workload, however, only a few studies have examined ultrastructural flexibility in avian muscle. Additionally, the relationship between myostatin, IGF-1, and satellite cell (SC) proliferation as it relates to avian muscle flexibility has not been addressed in birds and represents a promising avenue for future study.

Effect of expression of PPARG, DNM2L, RRAD, and LINGO1 on broiler chicken breast muscle satellite cell function

Disorders affecting the breast muscle of modern commercial broiler chickens have increased in recent years. Wooden Breast (WB) myopathy is characterized by a palpably hard breast muscle with increased fat deposition. WB is a metabolic disorder with lipid accumulation considered to be a primary causal factor. The adult myoblasts, satellite cells, are a partially differentiated stem cell population and primarily function in muscle growth and regeneration. The satellite cells also express adipogenic genes. The objective of this study was to determine the expression of the adipogenic genes PPARG, DNM2L, RRAD, and LINGO1 in commercial Ross 708 (708) and Randombred (RBch) satellite cells. RBch satellite cells are from commercial 1995 broilers before WB and 708 broilers are a modern commercial line. In general, expression of these genes was different between the 708 and RBch satellite cells during proliferation and differentiation. Expression of PPARG and RRAD were both significantly increased during both proliferation and differentiation in the 708 cells (P ≤ 0.05). Knocking down the expression of these genes with small interfering RNAs did not greatly affect either proliferation or differentiation. Lipid accumulation was affected by the knockdown of these genes with significant line effects from 48 h of proliferation through 72 h of differentiation. In general, 708 satellite cells had higher lipid levels. Knockdown treatment effect was specific to each gene. The results demonstrate that lipid biosynthesis has been affected in breast muscle satellite cells which may contribute to the increased lipid deposition in modern day commercial broiler chickens.

Temperature and Growth Selection Effects on Proliferation, Differentiation, and Adipogenic Potential of Turkey Myogenic Satellite Cells Through Frizzled-7-Mediated Wnt Planar Cell Polarity Pathway

Satellite cells (SCs) are a heterogeneous population of multipotential stem cells. During the first week after hatch, satellite cell function and fate are sensitive to temperature. Wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) signaling pathway is significantly affected by thermal stress in turkey pectoralis major (p. major) muscle SCs. This pathway regulates the activity of SCs through a frizzled-7 (Fzd7) cell surface receptor and two intracellular effectors, rho-associated protein kinase (ROCK) and c-Jun. The objective of the present study was to determine the effects of thermal stress, growth selection, and the Fzd7-mediated Wnt/PCP pathway on proliferation, myogenic differentiation, lipid accumulation, and expression of myogenic and adipogenic regulatory genes. These effects were evaluated in SCs isolated from the p. major muscle of 1-week faster-growing modern commercial (NC) line of turkeys as compared to SCs of a slower-growing historic Randombred Control Line 2 (RBC2) turkey line. Heat stress (43°C) increased phosphorylation of both ROCK and c-Jun with greater increases observed in the RBC2 line. Cold stress (33°C) had an inhibitory effect on both ROCK and c-Jun phosphorylation with the NC line showing greater reductions. Knockdown of the expression of Fzd7 decreased proliferation, differentiation, and expression of myogenic regulatory genes: myoblast determination factor-1 and myogenin in both lines. Both lipid accumulation and expression of adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ, CCAAT/enhancer-binding protein-β, and neuropeptide-Y were suppressed with the Fzd7 knockdown. The RBC2 line was more dependent on the Fzd7-mediated Wnt/PCP pathway for proliferation, differentiation, and lipid accumulation compared to the NC line. Thus, thermal stress may affect poultry breast muscle growth potential and protein to fat ratio by altering function and fate of SCs through the Fzd7-mediated Wnt/PCP pathway in a growth-dependent manner.

Thermal stress affects proliferation and differentiation of turkey satellite cells through the mTOR/S6K pathway in a growth-dependent manner

Satellite cells (SCs) are stem cells responsible for post-hatch muscle growth through hypertrophy and in birds are sensitive to thermal stress during the first week after hatch. The mechanistic target of rapamycin (mTOR) signaling pathway, which is highly responsive to thermal stress in differentiating turkey pectoralis major (p. major) muscle SCs, regulates protein synthesis and the activities of SCs through a downstream effector, S6 kinase (S6K). The objectives of this study were: 1) to determine the effect of heat (43°C) and cold (33°C) stress on activity of the mTOR/S6K pathway in SCs isolated from the p. major muscle of one-week-old faster-growing modern commercial (NC) turkeys compared to those from slower-growing Randombred Control Line 2 (RBC2) turkeys, and 2) to assess the effect of mTOR knockdown on the proliferation, differentiation, and expression of myogenic regulatory factors of the SCs. Heat stress increased phosphorylation of both mTOR and S6K in both turkey lines, with greater increases observed in the RBC2 line. With cold stress, greater reductions in mTOR and S6K phosphorylation were observed in the NC line. Early knockdown of mTOR decreased proliferation, differentiation, and expression of myoblast determination protein 1 and myogenin in both lines independent of temperature, with the RBC2 line showing greater reductions in proliferation and differentiation than the NC line at 38° and 43°C. Proliferating SCs are more dependent on mTOR/S6K-mediated regulation than differentiating SCs. Thus, thermal stress can affect breast muscle hypertrophic potential by changing satellite cell proliferation and differentiation, in part, through the mTOR/S6K pathway in a growth-dependent manner. These changes may result in irreversible effects on the development and growth of the turkey p. major muscle.

Do thermal acclimation and an acute heat challenge alter myonuclear domain of control- and fast-growing quail?

Efforts to determine physiological traits that may render species resilient or susceptible to changing global temperatures have accelerated in recent years. Temperature is of critical importance to biological function; thus, climate change has the potential to severely affect all levels of biological organization in many species. For example, increases in environmental temperatures may alter muscle structure and function in birds. Myonuclear domain (MND), an under-studied aspect of avian muscle physiology that changes in response to thermal stress, is defined as the amount of cytoplasm within a muscle fiber that each nucleus is responsible for servicing. Here, we used two random bred lines of Japanese quail (Coturnix japonica) representing examples of control and fast growth rates. We used a factorial design to administer four treatment combinations to each line - an initial period of either heat-stress acclimation (Acclimation) or no acclimation (Not acclimated) followed by either a heat-stress challenge (HS) or no challenge (NC) after week 8 of age - to determine the effects of thermal acclimation and acute thermal stress on quail MND. We found a significant interaction between line * final treatment with fast-growing, HS birds demonstrating the lowest numbers of nuclei per mm of fiber, and Acclimated control-growing birds showing the highest numbers of nuclei per mm of fiber. There was a significant effect of line on MND with the fast-growing line having larger MNDs. Initial treatment with Not Acclimated birds showed larger MNDs. Additionally, control growing quail demonstrated positive correlations with fiber size, whereas fast growing quail did not. This may mean that nuclei in larger fibers of fast-growing quail may be functioning maximally, and that increases in temperature may also demonstrate similar effects.

Gastrocnemius Muscle Structural and Functional Changes Associated with Domestication in the Turkey

Selection for increased muscle mass in domestic turkeys has resulted in muscles twice the size of those found in wild turkeys. This study characterizes muscle structural changes as well as functional differences in muscle performance associated with selection for increased muscle mass. We compared peak isometric force production, whole muscle and individual fiber cross-sectional area (CSA), connective tissue collagen concentration and structure of the lateral gastrocnemius (LG) muscle in wild and adult domestic turkeys. We also explored changes with age between juvenile and adult domestic turkeys. We found that the domestic turkey's LG muscle can produce the same force per cross-sectional area as a wild turkey; however, due to scaling, domestic adults produce less force per unit body mass. Domestic turkey muscle fibers were slightly smaller in CSA (3802 ± 2223 μm2) than those of the wild turkey (4014 ± 1831 μm2, p = 0.013), indicating that the absolutely larger domestic turkey muscles are a result of an increased number of smaller fibers. Collagen concentration in domestic turkey muscle (4.19 ± 1.58 μg hydroxyproline/mg muscle) was significantly lower than in the wild turkeys (6.23 ± 0.63 μg/mg, p = 0.0275), with visible differences in endomysium texture, observed via scanning electron microscopy. Selection for increased muscle mass has altered the structure of the LG muscle; however, scaling likely contributes more to hind limb functional differences observed in the domestic turkey.

Effect of Temperature and Selection for Growth on Intracellular Lipid Accumulation and Adipogenic Gene Expression in Turkey Pectoralis Major Muscle Satellite Cells

As multipotential stem cells, satellite cells (SCs) have the potential to express adipogenic genes resulting in lipid synthesis with thermal stress. The present study determined the effect of temperature on intracellular lipid synthesis and adipogenic gene expression in SCs isolated from the pectoralis major (p. major) muscle of 7-day-old fast-growing modern commercial (NC) turkeys compared to SCs from unselected slower-growing turkeys [Randombred Control Line 2 (RBC2)]. Since proliferating and differentiating SCs have different responses to thermal stress, three incubation strategies were used: (1) SCs proliferated at the control temperature of 38°C and differentiated at 43° or 33°C; (2) SCs proliferated at 43° or 33°C and differentiated at 38°C; or (3) SCs both proliferated and differentiated at 43°, 38°, or 33°C. During proliferation, lipid accumulation increased at 43°C and decreased at 33°C with the NC line showing greater variation than the RBC2 line. During proliferation at 43°C, peroxisome proliferator-activated receptor-γ (PPARγ) and neuropeptide-Y (NPY) expression was reduced to a greater extent in the NC line than the RBC2 line. At 33°C, expression of PPARγ, NPY, and CCAAT/enhancer-binding protein-β (C/EBPβ) was upregulated, but only in the RBC2 line. During differentiation, both lines showed greater changes in lipid accumulation and in C/EBPβ and NPY expression if the thermal challenge was initiated during proliferation. These data suggest that adipogenic gene expression is more responsive to thermal challenge in proliferating SCs than in differentiating SCs, and that growth-selection has increased temperature sensitivity of SCs, which may significantly affect breast muscle structure and composition.

Alpha-tocopherol acetate and alpha lipoic acid may mitigate the development of wooden breast myopathy in broilers at an early age

1. The objective of this study was to identify the effects of the antioxidant alpha-tocopherol acetate (ATA) and alpha lipoic acid (ALA) which have anti-inflammatory effects on developmental onset, severity and the progression of wooden breast (WB) based on Pectoralis major (P. major) muscle morphology and expression of genes associated with WB during the first three weeks post-hatch.2. A total of 160 newly hatched Ross 708 broiler chicks were randomly assigned in a replicated trial to either a control group or three dietary treatments (ATA 160 mg/kg feed, ALA 500 mg/kg feed or in combination).3. Microscopic changes associated with WB began at one week of age in all groups. The ATA acetate and ALA fed in combination decreased WB severity at two weeks of age (P = 0.05) and ATA alone or in combination reduced severity at three weeks of age compared to the control group (P = 0.05). Expression of myogenic determination factor 1 and peroxisome proliferator-activated receptor gamma was reduced in all dietary treatments compared to the control at three weeks of age (P ≤ 0.05), which suggested reduced muscle degeneration and lipid deposition.4. ATA and ALA fed both independently and in combination had a positive effect on mitigating WB severity microscopically as early as two weeks of age.

Prospect of early vascular tone and satellite cell modulations on white striping muscle myopathy

Polyphasic myodegeneration potentially causes severe physiological and metabolic disorders in the breast muscle of fast-growing broiler chickens. To date, the etiology of recent muscle myopathies, such as the white striping (WS) phenotype, is still unknown. White striping–affected breast meats compromise the water holding capacity and predispose muscle to poor vascular tone, leading to the deterioration of meat qualities. Herein, this review article provides insight on the complexities around chicken breast myopathies: (i) the etiologies of WS occurrence in chicken; (ii) the metabolic changes that occur in WS defect in pectoralis major; and (iii) the interactions between breast muscle physiology and vascular tone. It also addressed the effects of nutritional supplements on muscle myopathies on chicken breast meats. Moreover, the review explored breast muscle biology focusing on the early preparation of satellite and vascular cells in fast-growth chicken breeds. Transcriptomics and histological analyses revealed poor vascularity in breast muscle of fast growth chickens. Thus, we suggest in ovo feeding of nutrients promoting vascularization and satellite cells replenishment as a potential strategy to enhance endothelium-derived nitric oxide availability to promote vascularization in the pectoralis major muscle region.

Response of turkey pectoralis major muscle satellite cells to hot and cold thermal stress: Effect of growth selection on satellite cell proliferation and differentiation

Satellite cell (SCs), the main progenitors for post-hatch poultry muscle growth, has maximal mitotic activity and sensitivity to temperature during the first week after hatch. The objective of the present study was to determine the effect of hot and cold temperatures on the proliferation and differentiation of SCs from pectoralis major (P. major) muscle of fast-growing 1-week-old Nicholas commercial (NC) turkeys compared to Randombred Control Line 2 (RBC2) turkeys representing commercial turkeys from 1966. Three temperature regimens were used: SCs proliferation at 38 °C (control) with differentiation at 43° or 33 °C; proliferation at 43° or 33 °C with differentiation at 38 °C; or both proliferation and differentiation at 43°, 38°, or 33°C. Satellite cell proliferation and differentiation increased at 43 °C and decreased at 33 °C in both lines. When a thermal challenge was administered during proliferation, greater stimulatory or suppressive effects on differentiation were observed compared to if the thermal challenge was applied only during differentiation in both lines. Expression of myoblast determination protein 1 during proliferation showed a higher increase in the NC line compared to the RBC2 line at 43 °C. Increased myogenin expression was observed in all hot treatment groups in the NC line but was only observed in the RBC2 line if the hot treatment was administered throughout proliferation and differentiation. Cold treatment suppressed myogenin expression independent of line. These results suggest turkey P. major muscle SCs are more sensitive to environmental temperatures during proliferation, and SCs from growth-selected NC turkeys are more sensitive to thermal stress compared to the RBC2 turkeys.

Effect of early posthatch supplementation of vitamin E and omega-3 fatty acids on the severity of wooden breast, breast muscle morphological structure, and gene expression in the broiler breast muscle

Wooden breast (WB) has arisen primarily in the breast muscle of commercial broilers. It is characterized by palpation of a rigid pectoralis major (p. major) muscle and is under severe oxidative stress and inflammation. Previous studies have shown that vitamin E (VE) has antioxidant properties and omega-3 (n-3) fatty acids have an anti-inflammatory effect. The objectives of this study were to identify the effects of VE and n-3 fatty acids on the severity of WB, morphological structure of the p. major muscle, expression of genes likely associated with WB and to determine the most beneficial supplementation period. A total of 210 Ross 708 broilers were randomly assigned into 7 treatments with 10 replicates of 3 birds each. The control group received a corn–soybean meal basal diet during the entire study (0–58 d). Supplementation of VE (200 IU/kg), n-3 fatty acids (n-6/n-3 ratio of 3.2:1), or combination of both were fed during the starter phase (0–10 d) or grower phase (11–24 d). All broilers were harvested at 58 d of age. Morphological assessment of the p. major muscle included myofiber width, perimysial and endomysial connective tissue space, overall morphological structure, and scoring of WB microscopically. Gene expression was measured using nanostring analysis. Genes associated with muscle development and growth factors, inflammation, extracellular matrix, and glucose metabolism were differentially expressed in the p. major muscle of the broilers supplemented with VE in the grower diet. Greater than 2 times more giant myofibers (≥70 μm) were found in the group supplemented with VE and n-3 fatty acids in the starter diet compared with the group fed VE in the grower diet (P = 0.02). Microscopic evaluation showed that VE supplementation in the grower diet had a 16.19% increase in muscle with no WB compared with the control group (P = 0.05). These data suggest that supplementation of VE during the grower phase may reduce the severity of WB in broilers.

Muscle Abnormalities and Meat Quality Consequences in Modern Turkey Hybrids

Turkey meat is the second most consumed poultry meat worldwide and represents an economic source of high-quality protein for human consumption. To fulfill the increasing demand for turkey meat, breeding companies have been selecting genetic lines with increased growth potential and breast muscle proportion. Moreover, the progressive shift toward further processed products has emphasized the need for higher standards in poultry meat to improve its technological characteristics and functional properties (i.e., water-holding capacity). However, as observed for broiler chickens, a growing body of scientific evidence suggests that the intense selection for the aforementioned traits could be associated with a greater occurrence of growth-related myopathies and abnormalities and, consequently, to increased downgrading rates and overall reduction of meat quality characteristics. In the past, muscle abnormalities such as deep pectoral myopathy, pale-soft-and-exudative-like meat, and focal myopathy have been reported in turkey lines selected for increased growth rate. In addition, the presence of white striations in the superficial layer of pectoralis major muscle, as well as the tendency of muscle fiber bundles to separate resulting in an altered breast muscle structure, has been detected in commercial turkey abattoirs. Furthermore, past investigations revealed the presence of another quality issue depicted by an overall toughening of the breast muscle. These meat abnormalities seem to macroscopically overlap the white striping, spaghetti meat, and wooden breast conditions observed in pectoral muscle of fast-growing, high-breast-yield chicken hybrids, respectively. Considering the high economic impact of these growth-related abnormalities in broilers, there is an increasing interest of the turkey industry in estimating the occurrence and the impact of these meat quality issues also in the modern turkey lines. Studies have been recently conducted to assess the effect of the genotype on the occurrence of these emerging growth-related defects and to evaluate how meat quality properties are affected by white-striping condition in turkeys, respectively. Therefore, this review aims to provide a critical overview of the current understanding regarding the growth-related abnormalities and their impact on meat quality in modern turkey hybrids with the hope that this information may improve the knowledge concerning their overall effect on poultry meat.

Pectoralis Major (Breast) Muscle Extracellular Matrix Fibrillar Collagen Modifications Associated With the Wooden Breast Fibrotic Myopathy in Broilers

The poultry industry has placed significant emphasis on the selection of meat-type broilers for increased body weight, increased meat yield especially the pectoralis major (breast) muscle, decreased time to processing, and improved feed conversion_. Although significant improvements have occurred in fast-growing meat-type broilers, myopathies affecting meat quality especially in the pectoralis major muscle have occurred. Many of the broiler breast muscle myopathies are caused by inflammation leading to the necrosis of existing muscle fibers and resulting in replacement of the muscle fibers with extracellular matrix proteins especially fibrillar collagens, fibrosis. This review explores how the fibrotic deposition and organization of extracellular matrix proteins especially the fibrillar collagens, Types I and III, affects the phenotype of the Wooden Breast myopathy, functional properties of the pectoralis major muscle, and meat quality.

Research Note: The effect of selection for 16-week body weight on turkey serum metabolome

The phenotype of modern commercial turkeys is substantially different than that of unselected, heritage turkey lines. These phenotypic changes have arisen from alterations in the genome/transcriptome, as well as the influence of many external factors on growth performance including nutrition, environment, and management. To investigate the phenotypic changes resulting from genetic selection for increased body weight, The Ohio State University maintains 2 unique genetic turkey lines: the randombred control (RBC2) line, which is comprised of genetics from 1960 era commercial turkeys and has been maintained without conscious selection for any trait; and the F line, which was originally selected from the RBC2 line and has been selected for increased 16 wk body weight for over 50 generations. This study used broad-spectrum mass-spectrometry profiling techniques to identify and quantify differences in the metabolome of the serum of F and RBC2 turkey lines. Serum samples from both F and RBC2 turkeys were subject to quantitative time of flight liquid chromatography tandem mass spectrometry analyses. Principle component analyses showed distinct populations of metabolites in the F vs. RBC2 serum, suggesting that increased body weight is associated with the accumulation of several metabolites. Comparing the spectral features to online databases resulted in the selection of 104 features with potentially identifiable chemical structures. Of these 104 features, 25 were found at higher levels in the serum of the RBC2 line turkeys, while 79 were found at a greater abundance in the F line turkeys. A more detailed analysis of these 104 features allowed for the putative identification of 49 compounds, which were clustered into 6 functional groups: 1) energy metabolism; 2) vitamins; 3) hormones and signaling molecules; 4) lipid derivatives, fatty acid metabolites, and membrane components; 5) amino acid/protein metabolism; and 6) microbial metabolites. Further validation and experimentation is needed to confirm the identity of these metabolites and understand their biological relevance and association with selection for increased body weight.

Fibrillar Collagen Organization Associated with Broiler Wooden Breast Fibrotic Myopathy

Wooden breast (WB) is a fibrotic myopathy affecting the pectoralis major (p. major) muscle in fast-growing commercial broiler lines. Birds with WB are phenotypically detected by the palpation of a hard p. major muscle. A primary feature of WB is the fibrosis of muscle with the replacement of muscle fibers with extracellular matrix proteins, such as collagen. The ability of a tissue to be pliable and stretch is associated with the organization of collagen fibrils in the connective tissue areas surrounding muscle fiber bundles (perimysium) and around individual muscle fibers (endomysium). The objective of this study was to compare the structure and organization of fibrillar collagen by using transmission electron microscopy in two fast-growing broiler lines (Lines A and B) with incidence of WB to a slower growing broiler Line C with no phenotypically detectable WB. In Line A, the collagen fibrils were tightly packed in a parallel organization, whereas in Line B, the collagen fibrils were randomly aligned. Tightly packed collagen fibrils arranged in parallel are associated with nonpliable collagen that is highly cross-linked. This will lead to a phenotypically hard p. major muscle. In Line C, the fibrillar collagen was sparse in its distribution. Furthermore, the average collagen fibril diameter and banding D-period length were altered in Line A p. major muscles affected with WB. Taken together, these data are suggestive of different fibrotic myopathies beyond just what is classified as WB in fast-growing broiler lines.

Comparison of 2 commercial turkey hybrids: productivity, occurrence of breast myopathies, and meat quality properties

This study was undertaken to compare productive performance, occurrence of breast myopathies, chemical composition, and technological properties of the meat in 2 dominant commercial turkey hybrids. A total of 972 1-day-old male turkey poults (equally divided in hybrid A and B) were randomly distributed in 18 floor pens. Overall, productive performance resulted similar between the genotypes, although they showed different growth profile (turkeys from group B grew up faster up to 84 d). Regarding the occurrence of myopathies, the percentage of breasts affected by white striping was markedly higher in both genotypes (46 vs. 60% of severe lesions, respectively for A and B; P < 0.05), while the occurrence of spaghetti meat-like condition was negligible. The histological features of the different categories of meat abnormalities resulted similar to those previously described for chicken hybrids. The technological traits such as ultimate pH, lightness, redness, marinade uptake, cooking losses, and shear force were not significantly affected by the genotype. However, turkeys from group B exhibited lower yellowness (b*, 0.50 vs. 1.04; P < 0.05) and higher drip losses (1.34 vs. 1.26%; P < 0.05). The shelf-life test on thigh meat showed no significant changes in meat color over the storage time in both hybrids, whereas thigh meat from group A showed absolute lower values of lightness (L*) and yellowness (b*) (P < 0.05). Lipid oxidation of thigh meat significantly increased during storage, although no significant difference was found between the hybrids. Proximate composition and intramuscular collagen properties resulted similar between genetic lines with the exception of total fat content (1.55 vs. 1.21%, respectively for A and B; P < 0.05). The genotype had a moderate effect on fatty acid families of breast meat as only monounsaturated fatty acid content was significantly affected (31.7 vs. 29.8%, respectively for A and B). In conclusion, the overall productive traits of commercial turkeys, including the occurrence of muscle myopathies, as well as quality attributes of fresh and refrigerated meat were only slightly affected by the genotype.

Recent Developments in Breast Muscle Myopathies Associated with Growth in Poultry

The functional unit in skeletal muscle is the multinucleated myofiber, which is composed of parallel arrays of microfibrils. The myofiber and sarco-mere structure of skeletal muscle are established during embryogenesis, when mononuclear myoblast cells fuse to form multinucleated myotubes and develop into muscle fibers. With the myoblasts permanently unable to enter a proliferative state again after they fuse to form the multinucleated myotube, postnatal myofiber growth, muscle homeostasis, and myofiber regeneration are dependent on a myogenic stem cell, the satellite cell. Because the satellite cell is a partially differentiated stem cell controlling the state of skeletal muscle structure throughout the life of the bird, it can impact muscle development and structure, growth, and regeneration and, subsequently, meat quality. When myofibers are damaged, muscle repair is dependent on the satellite cells. Regenerated myofibers after the repair process should be similar to the original muscle fiber. Despite significant improvements in meat-type birds, degenerative myopathies have arisen. In many of these degenerative breast muscle myopathies, like Wooden Breast, satellite cell–mediated regeneration of muscle is suppressed. Thus, the biological function of avian myogenic satellite cells and their influence on cellular mechanisms affecting breast muscle development and growth, function during degenerative myopathies, and meat quality are discussed.

Isolation and Differentiation of Mesenchymal Stem Cells From Broiler Chicken Compact Bones

Chicken mesenchymal stem cells (MSCs) can be used as an avian culture model to better understand osteogenic, adipogenic, and myogenic pathways and to identify unique bioactive nutrients and molecules which can promote or inhibit these pathways. MSCs could also be used as a model to study various developmental, physiological, and therapeutic processes in avian and other species. MSCs are multipotent stem cells that are capable of differentiation into bone, muscle, fat, and closely related lineages and express unique and specific cell surface markers. MSCs have been isolated from numerous sources including human, mouse, rabbit, and chicken with potential clinical and agricultural applications. MSCs from chicken compact bones have not been isolated and characterized yet. In this study, MSCs were isolated from compact bones of the femur and tibia of day-old male broiler chicks to investigate the biological characteristics of the isolated cells. Isolated cells took 8–10 days to expand, demonstrated a monolayer growth pattern and were plastic adherent. Putative MSCs were spindle-shaped with elongated ends and showed rapid proliferation. MSCs demonstrated osteoblastic, adipocytic, and myogenic differentiation when induced with specific differentiation media. Cell surface markers for MSCs such as CD90, CD105, CD73, CD44 were detected positive and CD31, CD34, and CD45 cells were detected negative by PCR assay. The results suggest that MSCs isolated from broiler compact bones (cBMSCs) possess similar biological characteristics as MSCs isolated from other chicken tissue sources.

Waddle and shuffle: gait alterations associated with domestication in turkeys

Domestication has altered turkey morphology by artificially selecting for increased muscle mass and breast meat. Artificial selection has resulted in birds that weigh up to 3 times more than their wild counterparts, with relatively little change in the length of their bones and limbs. Considering these structural changes, it seems probable that domestic turkey locomotor kinematics and kinetics would also be altered. To examine the locomotor dynamics of wild and domestic turkeys, we had both strains walk down a runway with a force plate at the center to measure their ground reaction forces and gait parameters. The location of their center of mass was also quantified using a force plate and bi-planar x-ray and found to be further anterior in the domestic strain. The domestic turkeys locomoted across a lower range of speeds (0.25-1.64 ms^-1) than the wild turkeys (0.26-3.26 ms^-1) and increased their stride frequency at a higher rate. They also displayed large lateral oscillations, i.e. waddling, during walking that translated into relatively high medio-lateral ground reaction forces and lateral kinetic energy (3.5 times higher than that of wild turkeys). The results indicate that domestic turkey locomotion is not simply a slowed down version of wild turkey locomotion. The changes in gait observed are similar to the shuffling gait present in some human populations, such as Parkinson's patients, which serves to increase stability. The domestic turkey's increased body mass and more anterior center of mass position may require these kinematic and kinetic gait differences.

The Effect of Different Dietary Levels and Sources of Methionine on the Growth Performance of Turkeys, Carcass and Meat Quality

The aim of this study was to determine the effect of different dietary levels and sources of methionine (Met) on the growth performance of turkeys, carcass and meat quality. A total of 816 Hybrid Converter turkeys in 6 groups and 8 replications were fed wheat-soybean meal-based diets supplemented with three sources of Met: DL-isomer, L-isomer and DL-hydroxy analog (DLM, LM and MHA, respectively). In four 4-week periods (from 1 to 16 weeks of age), the Met content of turkey diets corresponded to the level recommended by NRC (1994) or was increased by approximately 50% to match the intake recommended by some breeding companies. Increased dietary Met content resulted in a higher final body weight (BW) of turkeys (P=0.002) and a lower feed conversion ratio (FCR) (P=0.049), but had no effect on carcass dressing percentage and most parameters of carcass quality. The higher dietary Met level contributed to a decrease in meat pH, a lower contribution of redness and a smaller muscle fiber diameter (P=0.028, P=0.040 and P=0.004, respectively). The higher dietary Met level had no influence on the redox status of meat, but it reduced the incidence of lymphoid cell infiltration between muscle fibers threefold (P=0.003). Throughout the experiment, no significant differences were noted in the growth performance parameters of turkeys, irrespective of Met source. MHA contributed to higher abdominal fat content, lower dry matter (DM) content and lower catalase (CAT) activity in breast meat, compared with DLM and LM. Increased dietary Met content, approximately 50% higher than that recommended by NRC (1994), regardless of Met source, led to higher final BW of turkeys, but had no effect on carcass dressing percentage and most parameters of carcass quality.

Muscle structure and gene expression in pectoralis major muscle in response to deep pectoral myopathy induction in fast- and slow-growing commercial broilers

1. The objective of this study was to determine muscle structure and gene expression in pectoralis major (p. major) muscle of broilers in response to deep pectoral myopathy (DPM) induction. 2. A total of 160 chickens from slow- and fast-growing broilers were raised under same conditions. Half of the broilers from each strain were encouraged to wing flap when they reached 2800 g body weight. Pectoralis minor (p. minor) muscle of the broilers was inspected for the occurrence of DPM and p. major samples were collected from broilers with or without DPM. The muscle fibre area and number, capillary number and the signalling pathways of vascular development (vascular endothelial growth factor A, VEGFA) and muscle contraction regulation (actin alpha 1, ACTA1; myosin light chain kinase 2, MYLK2 and ATPase Ca⁺² transporting gene 1, ATP2A1) were studied in p. major muscle. 3. DPM induction increased fibre area of p. major muscle with a greater rate in the slow-growing strain compared with fast-growing line. Although the capillary number was higher in slow-growing compared with fast-growing broilers, in the case of DPM induction, the number of capillaries was similar between strains. 4. Expression of VEGFA, MYLK2 and ATP2A1 was greater in slow- than in fast-growing broilers. DPM induction increased expression of ACTA1, VEGFA and ATP2A1 in p. major muscle of broilers from both strains; however, MYLK2 expression was downregulated. 5. Changes in capillary density and expression of VEGFA found in the p. major muscle of broilers with DPM suggest increased blood flow to increase oxygen availability. The upregulation of ATP2A1 by DPM induction could be attributable to alterations in calcium ion transportation from the cytoplasm into the sarcoplasmic reticulum. 6. The results are evidence of changes in muscle structure and gene expression pathways in p. major muscle of broilers with DPM.

Effect of white striping on turkey breast meat quality

In the past decades, the intense selection practices carried out in order to develop fast growing and high breast-yield turkey hybrids profoundly modified the muscle physiology leading to the development of growth-related alterations and muscular abnormalities. White striations of variable thickness have been particularly observed on the ventral surface of Pectoralis major muscle belonging from heavy male turkeys since several years. However, although the effects of white striping (WS) have been extensively studied on broilers, this condition was not considered as a main quality issue by both turkey producers and meat industry. Thus, this study aimed at evaluating whether the occurrence of WS in heavy male turkeys affects the quality traits and technological properties of meat to the same extent previously observed for broilers. In two replications, 72 Pectoralis major muscles were classified as: normal (NORM), moderate WS (MOD) and severe WS (SEV) cases. The whole muscle was weighed and cut in order to assess colour, ultimate pH, water holding (drip and cooking losses) and binding (marinade uptake) capacities, NMR relaxation properties, shear force as well as proximate composition of meat. The Pectoralis major muscles affected by WS (both moderate and severe cases) exhibited a one-fifth increased weight in comparison with their NORM counterpart. However, the occurrence of WS only partially affected the proximate composition of the meat. In detail, although moisture, collagen and protein contents did not differ among the groups, if compared with NORM, higher lipid levels were found in SEV muscles, whereas MOD had intermediate values. On the other hand, both MOD and SEV exhibited lower ash content. Despite these variations in proximate composition, both water holding and binding capacities of turkey breast meat were not affected by WS. Indeed, quality traits of raw (pH, colour, cooking losses and shear force) and marinated (uptake, cooking losses and shear force) meat as well as water distribution within the muscle tissue did not differ between NORM and WS cases. Overall, if compared with broilers, WS only marginally affected quality traits of turkey breast meat. It might thus be hypothesised a diverse specie-specific physiological response to the pressure in muscle tissue induced by the selection in turkeys that, although analogously led to the occurrence of WS, results in limited effects on meat quality.

Poultry Meat Quality in Relation to Muscle Growth and Muscle Fiber Characteristics

Variations in the definition of poultry meat quality exist because the quality traits are not solely based on intrinsic and extrinsic factors but also consumers’ preference. Appearance quality traits (AQT), eating quality traits (EQT), and reliance quality traits (RQT) are the major factors focused by the consumer before buying good quality of poultry meat. AQT and EQT of poultry meat are controlled by physical and biochemical characteristics of muscle fibers which can be categorized into a total number of fibers (TNF), cross-sectional area of fibers (CSAF), and fiber type composition (FTC). In poultry meat, it has been shown that muscle fiber properties play a key role in meat quality because numerous studies have reported the relationships between quality traits and fiber characteristics. Despite intensive research has been carried out to manipulate the muscle fiber to improve poultry meat quality, demand in a rapid growth of poultry muscle has correlated to the deterioration in the meat quality. The present paper reviews the definition of poultry meat quality, meat quality traits, and variations of meat quality. Also, this review presents recent knowledge underlying the relationship between poultry meat quality traits and muscle fiber characteristics.

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.

Methionine concentration in the pre-starter diet: its effect on broiler breast muscle development

The effect of feeding diets of variable methionine concentration on breast muscle development was assessed in Ross 308 broiler chicks. Four isonitrogenous and isoenergetic starter diets were formulated to contain 7.8, 5.9, 4.6, and 3.4 g methionine/kg diet, and were provided for the first 7 days post-hatch. At 7 days of age all birds were placed on an industry standard starter diet with 5.9 g methionine/kg diet until 14 days, and then provided standard broiler grower (until 28 days) and finisher (until 42 days) diets. Birds were weighed periodically throughout the study and feed intake and feed conversion ratio were determined. Ten birds per treatment were sacrificed and weighed on 0, 1, 4, 7, 14, 21, 28, 35, and 42 days. The pectoralis major (breast muscle) was then removed from the carcass and weighed. Samples of breast muscle were collected for genetic and histological analysis. Expression of the myogenic marker genes, myogenic differentiation factor 1 and myogenin, which regulate satellite cell activity, and the adipogenic marker gene, peroxisome proliferator-activated receptor gamma (PPARγ), was measured. Histological assessment of breast muscle morphology and fat deposition morphology was also performed. No effect of dietary treatment was observed on body or breast muscle weight, feed intake or feed conversion ratio. Marker gene expression was also similar in all treatment groups, except for PPARγ. Significantly higher expression of PPARγ was observed at 0 days in the 5.9 g methionine/kg diet treatment, before dietary treatments were provided. Expression of PPARγ did not differ among treatment groups on any subsequent day. Methionine dietary treatment had no effect on the morphological structure of the breast muscle, or intramuscular fat deposition. These results suggest that under the conditions of this study, satellite cell activity in the early post-hatch chick, and subsequent muscle development, were not responsive to the variable methionine manipulations tested in the pre-starter period.

Relationship of Skeletal Muscle Development and Growth to Breast Muscle Myopathies: A Review

Selection in meat-type birds has focused on growth rate, muscling, and feed conversion. These strategies have made substantial improvements but have affected muscle structure, repair mechanisms, and meat quality, especially in the breast muscle. The increase in muscle fiber diameters has reduced available connective tissue spacing, reduced blood supply, and altered muscle metabolism in the breast muscle. These changes have increased muscle fiber degeneration and necrosis but have limited muscle repair mechanisms mediated by the adult myoblast (satellite cell) population of cells, likely resulting in the onset of myopathies. This review focuses on muscle growth mechanisms and how changes in the cellular development of the breast muscle may be associated with breast muscle myopathies occurring in meat-type birds.

Temperature effect on proliferation and differentiation of satellite cells from turkeys with different growth rates

Poultry selected for growth have an inefficient thermoregulatory system and are more sensitive to temperature extremes. Satellite cells are precursors to skeletal muscle and mediate all posthatch muscle growth. Their physiological functions are affected by temperature. The objective of the current study was to determine how temperature affects satellite cells isolated from the pectoralis major (p. major) muscle (breast muscle) of turkeys selected for increased 16 wk body weight (F line) in comparison to a randombred control line (RBC2) from which the F line originated. Pectoralis major muscle satellite cells were thermally challenged by culturing between 33°C and 43°C to analyze the effects of cold and heat on proliferation and differentiation as compared to control temperature of 38°C. Expression levels of myogenic regulatory factors: myogenic differentiation factor 1 (MYOD1) and myogenin (MYOG) were quantified by quantitative polymerase chain reaction (qPCR). At all sampling times, proliferation increased at a linear rate across temperature in both the RBC2 and F lines. Differentiation also increased at a linear rate across temperature from 33 to 41°C at all sampling times in both the F and RBC2 lines. Satellite cells isolated from F line turkeys were more sensitive to both hot and cold temperatures as proliferation and differentiation increased to a greater extent across temperature (33 to 43°C) when compared with the RBC2 line. Expression of MYOD1 and MYOG increased as temperatures increased from 33 to 41°C at all sampling times in both the F and RBC2 lines. These results demonstrate that satellite cell function is sensitive to both cold and hot temperatures and p. major muscle satellite cells from F line turkeys are more sensitive to temperature extremes than RBC2 satellite cells.