Timing Is Everything-The High Sensitivity of Avian Satellite Cells to Thermal Conditions During Embryonic and Posthatch Periods

In ovo corticosterone exposure does not influence yolk steroid hormone relative abundance or skeletal muscle development in the embryonic chicken

In ovo corticosterone (CORT) exposure reportedly reduces growth and alters body composition traits in meat-type chickens. However, the mechanisms governing alterations in growth and body composition remain unclear but could involve myogenic stem cell commitment, and/or the presence of yolk steroid hormones. This study investigated whether in ovo CORT exposure influenced yolk steroid hormone content, as well as embryonic myogenic development in meat-type chickens. Fertile eggs were randomly divided at embryonic day (ED) 11 and administered either a control (CON; 100 µL of 10 mM PBS) or CORT solution (100 µL of 10 mM PBS containing 1 µg CORT) into the chorioallantoic membrane. Yolk samples were collected at ED 0 and ED 5. At ED 15 and hatch, embryos were humanely killed, and yolk and breast muscle (BM) samples were collected. The relative abundance of 15 steroid hormones, along with total lipid content was measured in yolk samples collected at ED 0, ED 5, ED 15, and ED 21. Muscle fiber number, cross-sectional area, and fascicle area occupied by muscle fibers were measured in BM samples collected at hatch. Relative expression of MyoD, MyoG, Pax7, PPARγ, and CEBP/β, and the sex steroid receptors were measured in BM samples collected at hatch. The administration of CORT had a limited effect on yolk steroid hormones. In ovo CORT significantly reduced fascicle area occupied by muscle fibers and CEBP/β expression was increased in CORT exposed birds at hatch. In addition, the quantity of yolk lipid was significantly reduced in CORT-treated birds. In conclusion, in ovo exposure to CORT does not appear to influence early muscle development through yolk steroid hormones in embryonic meat-type chickens however, the results provide a comprehensive analysis of the composition of yolk steroid hormones in ovo at different developmental time points. The findings may suggest increased mesenchymal stem cell commitment to the adipogenic lineage during differentiation and requires further investigation.

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.

Restricted feeding regimens improve white striping associated muscular defects in broiler chickens

The current study investigated the effects of intermittent feeding (IF) and fasting strategies at different times post-hatch on muscle growth and white striping (WS) breast development. In the first trial, 32 one-day-old Abor Acre broilers were fed ad libitum (AL) for 3 d post-hatch and then randomly allotted into 4 feeding strategies including AL, 1h-IF group (1 h IF, 4 times feeding/d, 1 h each time), 1.5h-IF (1.5 h IF, 4 times feeding/d, 1.5 h each time), and fasting (1d acute fasting, 6 d free access to feed) groups and fed for 7 d. Although angiogenic genes including VEGFA, VEGFR1, and VEGFR2, and myogenic genes including MYOG and MYOD were upregulated (P < 0.05), the breast muscle satellite cell (SC) number and PAX7, MYF5 expression were decreased by the IF strategies (P < 0.05). One-day fasting at 6 d of age also upregulated angiogenic genes and MYOD expression (P < 0.05), downregulated MYF5 expression (P < 0.05), but did not change SC number (P > 0.05). In the second trial, 384 one-day-old birds were fed AL for 1 wk and then randomly allotted to the above 4 feeding strategies starting at 8 d of age until 42 d of age. Similarly, IF and fasting strategies upregulated the expression of angiogenic and myogenic genes (P < 0.05). Both 1h-IF and 1.5h-IF increased breast muscle SC number (P < 0.05). At slaughter, breast muscle fiber diameter of 1.5h-IF was smaller but the SC number was larger than that of the birds fed AL (P < 0.05). The IF and fasting strategies prevented WS development, and reduced breast WS scores and triglyceride content (P < 0.05) without changing the body weight (P > 0.05). Fasting and 1h-IF reduced the expression of adipogenic genes ZNF423 and PDGFRα (P < 0.05). Moreover, IF and fasting strategies reduced fibrosis in breast muscle and reduced skeletal muscle-specific E3 ubiquitin ligases (TRIM63 and MAFBX) (P < 0.05). Fasting significantly reduced CASPASE-3 in breast muscle (P < 0.05). In conclusion, IF starting in the first week decreases SC number. Compared to AL, IF or fasting promotes muscular angiogenesis, increases SC number, prevents muscle degeneration, and prevents the development of WS without impairing the growth performance of broiler chickens.

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.

Impact of growth curve and dietary energy-to-protein ratio of broiler breeders on offspring quality and performance

The impact of growth curve (GC) and dietary energy-to-protein ratio of broiler breeder hens on chick quality and broiler performance was investigated. Pullets (n = 1,536) were randomly allotted to 24 pens and assigned to 1 of 8 treatments from hatch onwards, according to a 2 × 4 factorial arrangement with 2 GC (standard growth curve = SGC or elevated growth curve = EGC, +15%) and 4 diets, differing in energy-to-protein ratio (96%, 100%, 104%, and 108% AME_n diet). At 28 and 36 wk of age, 60 hatching eggs per maternal pen were selected for incubation and 768-day-old broilers were assigned to 32 pens according to maternal treatment.

Broilers from EGC breeders were 1.9 g heavier at hatch (P < 0.001) and 36 g heavier at slaughter (P = 0.001) than broilers from SGC breeders due to a 1.0 g/d higher growth rate (P = 0.003) and 1.5 g/d higher feed intake (P = 0.006) from hatch to 32 d of age. An increase in breeder dietary energy-to-protein ratio resulted in a linear decrease in embryonic mortality in the first 3 d of incubation (β = -0.2% per % AME_n; P = 0.05). At hatch, broiler BW decreased with an increasing breeder dietary energy-to-protein ratio (β = -0.1 g per % AME_n; P = 0.001), whereas at slaughter broiler BW increased with an increasing breeder dietary energy-to-protein ratio (β = 3.2 g per % AME_n; P = 0.02). This was due to a linear increase in growth rate (β = 0.1 g/d per % AME_n; P = 0.004) and feed intake (β = 0.1 g/d per % AME_n; P = 0.02). Additionally, an increase in breeder dietary energy-to-protein ratio resulted in a linear decrease in body weight corrected feed conversion ratio (β = -0.002 per % AME_n; P = 0.002). Overall, it can be concluded that a higher GC of breeders and an increase in breeder dietary energy-to-protein ratio enhances offspring performance.

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.

Mitigating the detrimental effects of heat stress in poultry through thermal conditioning and nutritional manipulation

The poultry industry faces several obstacles and challenges, including the changes in global temperature, increase in the per capita demand for meat and eggs, and the emergence and spread of various diseases. Among these, environmental challenges are one of the most severe hurdles impacting the growth and productivity of poultry. In particular, the increasing frequency and severity of heat waves over the past few years represent a major challenge, and this is expected to worsen in the coming decades. Chickens are highly susceptible to high ambient temperatures (thermal stress), which negatively affect their growth and productivity, leading to enormous economic losses. In the light of global warming, these losses are expected to increase in the near future. Specifically, the worsening of climate change and the rise in global temperatures have augmented the adverse effects of heat on poultry production worldwide. At present, the world population is approximately 7.9 billion, and it has been predicted to reach 9.3 billion by 2050 and approximately 11 billion by 2100, implying a great demand for protein supply; therefore, strategies to mitigate future poultry challenges must be urgently devised. To date, several mitigation measures have been adopted to minimize the negative effects of heat stress in poultry. Of these, thermal acclimation at the postnatal stage or throughout the embryonic stages has been explored as a promising approach; however, for large-scale application, this approach warrants further investigation to determine the suitable temperature and poultry age. Moreover, molecular mechanisms governing thermal conditioning are poorly understood. To this end, we sought to expand our knowledge of thermal conditioning in poultry, which may serve as a valuable reference to improve the thermotolerance of chickens via nutritional management and vitagene regulation. Vitagenes regulate the responses of poultry to diverse stresses. In recent years, nutritionists have paid close attention to bioactive compounds such as resveratrol, curcumin, and quercetin administered alone or in combination. These compounds activate vitagenes and other regulators of the antioxidant defense system, such as nuclear factor-erythroid 2-related factor 2. Overall, thermal conditioning may be an effective strategy to mitigate the negative effects of heat stress. In this context, the present review synthesizes information on the adverse impacts of thermal stress, elucidating the molecular mechanisms underlying thermal conditioning and its effects on the acquisition of tolerance to acute heat stress in later life. Finally, the role of some polyphenolic compounds, such as resveratrol, curcumin, and quercetin, in attenuating heat stress through the activation of the antioxidant defense system in poultry are discussed.

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.

Function of Chick Subcutaneous Adipose Tissue During the Embryonic and Posthatch Period

Since excess abdominal fat is one of the main problems in the broiler industry for the development of modern broiler and layer industry, the importance of subcutaneous adipose tissue has been neglected. However, chick subcutaneous adipose tissue appeared earlier than abdominal adipose tissue and more than abdominal adipose tissue. Despite a wealth of data, detailed information is lacking about the development and function of chick subcutaneous adipose tissue during the embryonic and posthatch period. Therefore, the objective of the current study was to determine the developmental changes of adipocyte differentiation, lipid synthesis, lipolysis, fatty acid β-oxidation, and lipid contents from E12 to D9.5. The results showed that subcutaneous adipose tissue was another important energy supply tissue during the posthatch period. In this stage, the mitochondrial copy number and fatty acid β-oxidation level significantly increased. It revealed that chick subcutaneous adipose tissue not only has the function of energy supply by lipidolysis but also performs the same function as brown adipose tissue to some extent, despite that the brown adipose tissue does not exist in birds. In addition, this finding improved the theory of energy supply in the embryonic and posthatch period and might provide theoretical basis on physiological characteristics of lipid metabolism in chicks.

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.

Effects of Heat Waves During Post-natal Development on Mitochondrial and Whole Body Physiology: An Experimental Study in Zebra Finches

Human-induced climate change is increasing the frequency, duration, and intensity of heat waves and exposure to these extreme temperatures impacts individual physiology and performance (e.g., metabolism, water balance, and growth). These traits may be susceptible to thermal conditions experienced during embryonic development, but experiments focusing on post-natal development are scant. Documented effects of heat waves on whole-body metabolism may reflect changes in mitochondrial function, but most studies do not measure physiological traits at both the cellular and whole organism levels. Here, we exposed nests of zebra finches to experimentally simulated heat waves for 18 days after hatching and measured body mass, growth rate, whole-body metabolic rate, body temperature, wet thermal conductance, evaporative water loss, and relative water economy of chicks at three ages corresponding to ectothermic (day 5), poikilothermic (day 12), and homoeothermic (day 50) stages. Additionally, we measured mitochondrial bioenergetics of blood cells 80 days post-hatch. While early-life exposure to heat wave conditions did not impact whole body metabolic and hygric physiology, body temperature was lower for birds from heated compared with control nests at both 12 and 50 days of age. There was also an effect of nest heating at the cellular level, with mitochondria from heated birds having higher endogenous and proton-leak related respiration, although oxidative phosphorylation, maximum respiratory capacity, and coupling efficiency were not impacted. Our results suggest that early-life exposure to high ambient temperature induces programming effects on cellular-level and thermal physiology that may not be apparent for whole-animal metabolism.

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.

The Role of Incubation Conditions in the Onset of Avian Myopathies

White striping, wooden breast, and spaghetti muscle have become common myopathies in broilers worldwide. Several research reports have indicated that the origin of these lesions is metabolic disorders. These failures in normal metabolism can start very early in life, and suboptimal incubation conditions may trigger some of the key alterations on muscle metabolism. Incubation conditions affect the development of muscle and can be associated with the onset of myopathies. A series of experiments conducted with broilers, turkeys, and ducks are discussed to overview primary information showing the main changes in breast muscle histomorphology, metabolism, and physiology caused by suboptimal incubation conditions. These modifications may be associated with current myopathies. Those effects of incubation on myopathy occurrence and severity have also been confirmed at slaughter age. The impact of egg storage, temperature profiles, oxygen concentrations, and time of hatch have been evaluated. The effects have been observed in diverse species, genetic lines, and both genders. Histological and muscle evaluations have detected that myopathies could be induced by extended hypoxia and high temperatures, and those effects depend on the genetic line. Thus, these modifications in muscle metabolic responses may make hatchlings more susceptible to develop myopathies during grow out due to thermal stress, high-density diets, and fast growth rates.