Thermal manipulations in late-term chick embryos have immediate and longer term effects on myoblast proliferation and skeletal muscle hypertrophy

Embryonic heat conditioning increases lipolytic gene expression in broiler chicks at day 4 post-hatch

Introduction

Exposure to elevated temperatures during incubation is known to induce epigenetic changes that are associated with immunological and stress-response differences at a later age. Reports on its effects on the adipose tissue are still scarce. In this experiment, we investigated the effect of embryonic heat conditioning (EHC) on growth, adipose tissue mRNA and global DNA methylation in broiler chicks at day 4 post-hatch.

Methods

Fertile eggs were divided into two groups: control and EHC. Eggs in the control group were incubated at 37.8°C and 80% relative humidity from day 0 to day 18.5 (E0 to E18.5). The EHC eggs were subjected to an intermittent increase in temperature to 39.5°C and 80% relative humidity from E7 to E16 for 12 h (07:30-19:30) per day. On day 4 post-hatch, control and EHC chicks were subjected to 36°C using three time points: 0 (no heat challenge serving as the control), and 2 and 12 h relative to start of the heat challenge. Fifteen chicks were sampled from each group for every timepoint. Body weight was recorded before euthanasia and subcutaneous adipose tissue was collected.

Results

Body weights were similar in control and EHC groups. Diacylglycerol O-acyltransferase 2 (DGAT2) mRNA was lower in the EHC group at time 0 relative to control. Hormone-sensitive lipase (HSL) mRNA was greater in the EHC than control group at the 0 h timepoint. Heat challenge affected adipose tissue DNA methylation, with methylation highest at 12 h into the heat challenge.

Discussion

These findings highlight the dynamic molecular responses of chicks to heat stress during early post-hatch development and suggest that EHC may affect heat stress responses and adipose tissue development through mechanisms involving lipid remodeling and DNA methylation.

Temperature manipulation during incubation: effect on embryo development and incidence of white striping and expression of related genes in broiler chickens from two commercial breeds

1. This study evaluated the effects of cyclic eggshell temperature between 10 and 14 d of embryogenesis on traits viz. the expression of MYOZ2, PPARγ and GPx7 in breast muscle, meat quality and incidence of white striping at slaughter age.2. Eggs were obtained from Cobb and Ross broiler breeders to investigate the response of breeds to eggshell temperature, which regulated air temperature. A total of 784 eggs were incubated at either the control eggshell temperature (37.8°C) from 0 to 18 d or exposed to cyclic high eggshell temperature (CHT) at 38.8°C for 6 h/d between 10 and 14 d of incubation. The temperature was 36.8°C between 18 and 21 d. Hatched chicks were reared under optimum rearing conditions. The birds were sampled at 19 d of incubation, at hatch and at 42 d post-hatch.3. There was no effect of eggshell temperature on yolk-free body weight and residual yolk sac weight. The CHT chicks had wider breasts on the day of hatching.4. At hatch and 42d post-hatch, PPARγ expression in Cobb-CHT was upregulated 4.78-fold and downregulated 3.28-fold, respectively, compared to the Cobb-control. At slaughter age, chickens from Ross-CHT had 1.98- and 2.33-fold upregulated PPARγ and GPX7 expressions, respectively, compared to Ross-control. The CHT increased GPx7 expression in the Cobb-CHT day-old chicks compared to the Cobb-control. On ED19, MYOZ2 expression was upregulated in Cobb and downregulated in Ross by CHT.5. The effects of breed and eggshell temperature on pH15, L*, a*, expressible juice and cooking loss were not significant. The CHT increased the incidence of severe white striping lesions in Ross chickens.6. It was concluded eggshell temperature modulated embryo development, incidence of white striping and expression of related genes differently in the two commercial breeds.

Embryonic thermal manipulation: a potential strategy to mitigate heat stress in broiler chickens for sustainable poultry production

Due to high environmental temperatures and climate change, heat stress is a severe concern for poultry health and production, increasing the propensity for food insecurity. With climate change causing higher temperatures and erratic weather patterns in recent years, poultry are increasingly vulnerable to this environmental stressor. To mitigate heat stress, nutritional, genetic, and managerial strategies have been implemented with some success. However, these strategies did not adequately and sustainably reduce the heat stress. Therefore, it is crucial to take proactive measures to mitigate the effects of heat stress on poultry, ensuring optimal production and promoting poultry well-being. Embryonic thermal manipulation (TM) involves manipulating the embryonic environment's temperature to enhance broilers' thermotolerance and growth performance. One of the most significant benefits of this approach is its cost-effectiveness and saving time associated with traditional management practices. Given its numerous advantages, embryonic TM  is a promising strategy for enhancing broiler production and profitability in the poultry industry. TM increases the standard incubation temperature in the mid or late embryonic stage to induce epigenetic thermal adaption and embryonic metabolism. Therefore, this review aims to summarize the available literature and scientific evidence of the beneficial effect of pre-hatch thermal manipulation on broiler health and performance.

Influence of incubation temperature, maternal effects, and paternity on quality of olive ridley hatchlings (Lepidochelys olivacea) from a mass-nesting beach in the Mexican Pacific

Future climate change scenarios project that the increase in surface temperatures will affect ocean temperatures, inducing shifts in marine biodiversity. Sea turtles are species that are particularly vulnerable to the effects of climate change because temperature is a factor that influences embryonic development. We collected clutches of olive ridley turtles from a mass-nesting beach in the Mexican Pacific, which were incubated in ex situ conditions. When the hatchlings emerged, we measured the body condition index-which evaluates the weight-length relationship-and swim thrust, both were considered traits associated with fitness, termed "fitness proxies," and evaluated the effects of incubation temperature, maternal effects, and paternity on these fitness proxies. The body condition index was correlated positively and significantly with the arribada month and temperature during the last third of the incubation period but showed an inverse relationship with the maternal effect. While swim thrust was positively correlated with the maternal effect and the arribada month, there was an inverse relationship with incubation temperature during the first third of the period. Paternity, whether single or multiple, did not have a significant effect on either fitness proxies; however, it may have effects on the average fitness of a population of hatchlings. These results underscore the need to expand research on the sublethal effects of high incubation temperatures on the adaptation and survival of sea turtles, particularly in scenarios of rapid climate change.

Climate change and its effects on body size and shape: the role of endocrine mechanisms

In many organisms, rapidly changing environmental conditions are inducing dramatic shifts in diverse phenotypic traits with consequences for fitness and population viability. However, the mechanisms that underlie these responses remain poorly understood. Endocrine signalling systems often influence suites of traits and are sensitive to changes in environmental conditions; they are thus ideal candidates for uncovering both plastic and evolved consequences of climate change. Here, we use body size and shape, a set of integrated traits predicted to shift in response to rising temperatures with effects on fitness, and insulin-like growth factor-1 as a case study to explore these ideas. We review what is known about changes in body size and shape in response to rising temperatures and then illustrate why endocrine signalling systems are likely to be critical in mediating these effects. Lastly, we discuss research approaches that will advance understanding of the processes that underlie rapid responses to climate change and the role endocrine systems will have. Knowledge of the mechanisms involved in phenotypic responses to climate change will be essential for predicting both the ecological and the long-term evolutionary consequences of a warming climate. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Embryonic thermal manipulation of poultry birds: Lucrative and deleterious effects

The major efforts to improve feed conversion, increase the body weight and breast muscle yield of broilers have been focused on feeding and management at the post hatch period. However, incubation temperature is the most significant factor for the egg hatching rate, chick quality, and post hatch performance. Therefore, incubation factors affecting the performance should be taken with necessary precautions. Incubation temperature not only affects the early development of the hatchlings but also has a lasting impact on the characteristics of the chicks, such as final body weight and meat quality traits. This article provides an overview about embryonic thermal manipulation (TM) of domestic fowls and review the lucrative and deleterious effects of embryonic TM on embryo development, muscle growth, thermotolerance acquisition, and immunity.

Growth performance, histological and physiological responses of heat-stressed broilers in response to short periods of incubation during egg storage and thermal conditioning

The short periods of incubation during egg storage (SPIDES) method enhances the quality of chicks and improves hatching rates. Additionally, embryonic thermal conditioning (TC) is a technique used to enhance thermotolerance in birds. Previous studies have evaluated the effects of SPIDES and embryonic TC separately. Yet, our hypothesis postulated that a synergistic effect could be achieved by integrating TC and SPIDES, thereby enhancing the broilers' resilience to thermal stress. We conducted an experiment involving 800 Ross broiler eggs, divided into two groups. The first group, referred to as S0, was maintained under standard storage room conditions and acted as our control group. The second group, known as S1, underwent a process called SPIDES for 5 h at a temperature of 37.8 ± 0.1 °C, on three occasions: days 5, 10, and 15 following egg collection. Upon reaching the 14th day of incubation (DOI), each of these primary groups was randomly subdivided into two equal subgroups. The control subgroup, designated as TC0, remained in the usual incubation conditions. Meanwhile, the other subgroup, TC1, was subjected to prenatal heat conditioning at a temperature of 39.5 ± 0.1 °C for 6 h per day, commencing on the 14th embryonic day (E) and extending until the 18th embryonic day (E). This experimental setup resulted in four distinct experimental subgroups: S0TC0, S1TC0, S0TC1, and S1TC1. The findings indicated that the combined application of SPIDES and TC had a significant positive effect on chick performance after hatching. Specifically, the (S1TC1) group exhibited the heaviest live body weight (LBW) and body weight gain (BWG) at the marketing age in comparison to the other groups. Furthermore, both SPIDES and TC had a positive influence on the relative weights of breast muscles and their histological measurements. The (S1TC1) group displayed significantly higher values in terms of the relative weight of breast muscles and the number of myocytes. In conclusion, SPIDES and TC have beneficial effects on pre- and post-hatch characteristics of broiler chicks up until the marketing age. Additionally, TC techniques improve chick performance, particularly under conditions of heat stress, and enhance the yield of breast muscle in later stages of life.

In-ovo feeding with creatine monohydrate: implications for chicken energy reserves and breast muscle development during the pre-post hatching period

The most dynamic period throughout the lifespan of broiler chickens is the pre-post-hatching period, entailing profound effects on their energy status, survival rate, body weight, and muscle growth. Given the significance of this pivotal period, we evaluated the effect of in-ovo feeding (IOF) with creatine monohydrate on late-term embryos' and hatchlings' energy reserves and post-hatch breast muscle development. The results demonstrate that IOF with creatine elevates the levels of high-energy-value molecules (creatine and glycogen) in the liver, breast muscle and yolk sac tissues 48 h post IOF, on embryonic day 19 (p < 0.03). Despite this evidence, using a novel automated image analysis tool on day 14 post-hatch, we found a significantly higher number of myofibers with lower diameter and area in the IOF creatine group compared to the control and IOF NaCl groups (p < 0.004). Gene expression analysis, at hatch, revealed that IOF creatine group had significantly higher expression levels of myogenin (MYOG) and insulin-like growth factor 1 (IGF1), related to differentiation of myogenic cells (p < 0.01), and lower expression of myogenic differentiation protein 1 (MyoD), related to their proliferation (p < 0.04). These results imply a possible effect of IOF with creatine on breast muscle development through differential expression of genes involved in myogenic proliferation and differentiation. The findings provide valuable insights into the potential of pre-hatch enrichment with creatine in modulating post-hatch muscle growth and development.

Effect of standard and physiological cell culture temperatures on in vitro proliferation and differentiation of primary broiler chicken pectoralis major muscle satellite cells

Culture temperatures for broiler chicken cells are largely based on those optimized for mammalian species, although normal broiler body temperature is typically more than 3°C higher. The objective was to evaluate the effects of simulating broiler peripheral muscle temperature, 41°C, compared with standard temperature, 38°C, on the in vitro proliferation and differentiation of primary muscle-specific stem cells (satellite cells; SC) from the pectoralis major (PM) of broiler chickens. Primary SC cultures were isolated from the PM of 18-day-old Ross 708 × Yield Plus male broilers. SC were plated in triplicate, 1.8-cm2, gelatin-coated wells at 40,000 cells per well. Parallel plates were cultured at either 38°C or 41°C in separate incubators. At 48, 72, and 96 h post-plating, the culture wells were fixed and immunofluorescence-stained to determine the expression of the myogenic regulatory factors Pax7 and MyoD as well as evaluated for apoptosis using a TUNEL assay. After 168 h in culture, plates were immunofluorescence-stained to visualize myosin heavy chain and Pax7 expression and determine myotube characteristics and SC fusion. Population doubling times were not impacted by temperature (p ≥ 0.1148), but culturing broiler SC at 41°C for 96 h promoted a more rapid progression through myogenesis, while 38°C maintained primitive populations (p ≤ 0.0029). The proportion of apoptotic cells increased in primary SC cultured at 41°C (p ≤ 0.0273). Culturing at 41°C appeared to negatively impact fusion percentage (p < 0.0001) and tended to result in the formation of thinner myotubes (p = 0.061) without impacting the density of differentiated cells (p = 0.7551). These results indicate that culture temperature alters primary broiler PM SC myogenic kinetics and has important implications for future in vitro work as well as improving our understanding of how thermal manipulation can alter myogenesis patterns during broiler embryonic and post-hatch muscle growth.

Thermal conditioning of quail embryos has transgenerational and reversible long-term effects

BACKGROUND

In the current context of global warming, thermal manipulation of avian embryos has received increasing attention as a strategy to promote heat tolerance in avian species by simply increasing the egg incubation temperature. However, because of their likely epigenetic origin, thermal manipulation effects may last more than one generation with consequences for the poultry industry. In this work, a multigenerational and transgenerational analysis of thermal manipulation during embryogenesis was performed to uncover the long-term effects of such procedure.

RESULTS

Thermal manipulation repeated during 4 generations had an effect on hatchability, body weight, and weight of eggs laid in Japanese quails, with some effects increasing in importance over generations. Moreover, the effects on body weight and egg weight could be transmitted transgenerationally, suggesting non-genetic inheritance mechanisms. This hypothesis is reinforced by the observed reversion of the effect on growth after five unexposed generations. Interestingly, a beneficial effect of thermal manipulation on heat tolerance was observed a few days after hatching, but this effect was not transgenerational.

CONCLUSIONS

Our multigenerational study showed that thermal conditioning of quail embryos has a beneficial effect on post-hatch heat tolerance hampered by transgenerational but reversible defects on growth. Assuming that no genetic variability underlies these changes, this study provides the first demonstration of epigenetic inheritance of traits induced by environmental temperature modification associated with long-term impacts in an avian species.

Naked neck gene and intermittent thermal manipulations during embryogenesis improve posthatch performance and thermotolerance in slow-growing chickens under tropical climates

Many studies have shown that thermal manipulations during the incubation (TMI) and naked neck gene (Na) positively affect heat-stressed broilers' thermotolerance, hatching process, and posthatch performance. Their combination could increase the beneficial effect on broilers reared under natural tropical climatic conditions. The aim of this study was to investigate the effects of the Na gene and TMI on hatching and posthatch performance of slow-growing broilers under tropical climates. The study included 1,200 hatching eggs from 2 different crosses: 1) females and males, both with a normal or fully feathered neck (na na group), and 2) females (with a normal neck) and males (bare neck) (Na na group), incubated in similar conditions until d 7. Thereafter, they were assigned to 3 subgroups for each cross: the control group (C) was incubated at standard incubation conditions (37.8°C, 60% RH). The TMI-1 group was subjected to TMI-1 (T = 38.5°C, RH = 65%, E10-18, 6 h/d) and TMI-2 group to TMI-2 (T = 39.5°C, RH = 65%, E7-16, 12 h/d). Between 450 and 504 h of incubation, eggs were checked for hatching events. During the posthatch phase, chicks from each incubation subgroups (Na na-C, Na na-TMI-1, Na na-TMI-2, na na-C, na na-TMI-1, na na-TMI-2) were raised for 12 wk at a tropical natural ambient temperature. Hatchability, hatching time, chick's temperature, final body weight (FBW), and feed conversion ratio (FCR) were determined. The results revealed that the Na gene reduced (P ˂ 0.05) hatchability. The control group had the highest mortality rate compared to TMI-1 and TMI-2 groups. There was an interaction between genotype and TMI on incubation duration, hatching weight, chick quality, FBW, and FCR (P ˂ 0.05). In conclusion, the Na gene influenced the effects of thermal manipulation. TMI-1 combined with Na gene improved the productive performances of broilers in a tropical climate.

A deep learning-based automated image analysis for histological evaluation of broiler pectoral muscle

Global market demand for chicken breast muscle with high yield and quality, together with the high incidence rate of breast muscle abnormalities in recent years highlights the need for tools that can provide a rapid and precise evaluation of breast muscle development and morphology. In this study, we used a novel deep learning-based automated image analysis workflow combining Fiji (ImageJ) with Cellpose and MorphoLibJ plugins to generate an automated diameter and cross-sectional area quantification for broiler breast muscle. We compared data of myofiber diameter from 14-day-old broiler chicks, generated either by manual analysis or by automated analysis. Comparison between manual and automated analysis methods exhibited a striking accuracy rate of up to 99.91%. Moreover, the automated analysis method was much faster. When the automated analysis method was implemented on 84 breast muscle cross-section images it characterized 59,128 myofibers within 4.2 h, while manual analysis of 27 breast muscle cross-section images enabled analysis of 17,333 myofibers in 54 h. The automated image analysis method was also more productive, producing data sets of both diameter and cross-sectional area at an 80-fold higher rate than the manual analysis (26,279 vs. 321 data sets per hour, respectively). In order to demonstrate the ability of this automated image analysis tool to detect differences in breast muscle histomorphology, we applied it on cross sections from chicks of control and in ovo feeding group, injected with a methionine source [2-hydroxy-4-(methylthio) butanoic calcium salt (HMTBa)], known to effect skeletal muscle histomorphology. Analysis was performed on 19,807 myofibers from the control group and 21,755 myofibers from the HMTBa group and was completed in less than 1 h. The clear advantages of this automated image analysis workflow characterized by high precision, high speed, and high productiveness demonstrate its potential to be implemented as a reproducible and readily adaptable research or diagnostic tool for chicken breast muscle development and morphology.

Optimization of embryonic thermal programming confirms increased liver fattening in mule ducks and changes in lipid metabolism

Introduction: The embryonic thermal programming (TM) in birds has been shown to impact several physiological parameters such as resistance to thermal stress, muscle growth or immunity. In mule ducks, it has recently been shown that TM can induce metabolic programming resulting in increased liver weight and fat storage after overfeeding. However, a decrease in hatchability and foie gras quality was also observed, suggesting that this technique needs to be optimized. Here, we tested a new thermal manipulation condition determined with the objective of avoiding negative impacts while maintaining or improving liver properties. Methods: The eggs of the control group were incubated at 37.6°C during the whole incubation period while those of the experimental group (TM group) were incubated at 39.3°C 16 h/24 h from the 11^th day of incubation to the 21^st. After hatching, all the animals were fed and raised under the same conditions until the age of 12 weeks. At this stage, one part of the animals was overfed and then slaughtered 2 h (to measure rapid changes in metabolism) or 10 h after the last meal (to obtain the best technological yields), while the other part was ration-fed and slaughtered 2 h after the last meal, at the same age. Results: An 8% increase in foie gras production was measured in the TM group compared to the control group without altering the quality of the final product (nor hatchability), confirming the successful optimization of the metabolic programming. Interestingly, these results allowed us not to reject the previously suggested hypothesis of a potential delay in metabolic processes involved in liver fattening in programmed animals, in particular by measuring a trend reversal regarding the amount of total hepatic lipids in both groups at 2 h and then 10 h after the last meal. Discussion: This study therefore validates the optimization of metabolic programming by embryonic thermal manipulation for duck liver fattening. The understanding of the mechanisms of embryonic thermal programming in birds remains today very incomplete and the search for epigenetic marks (main hypothesis of the concept of programming) at the origin of the observed phenotypes could be the next step of this work.

Heat Shock Protein Response to Stress in Poultry: A Review

Compared to other animal species, production has dramatically increased in the poultry sector. However, in intensive production systems, poultry are subjected to stress conditions that may compromise their well-being. Much like other living organisms, poultry respond to various stressors by synthesising a group of evolutionarily conserved polypeptides named heat shock proteins (HSPs) to maintain homeostasis. These proteins, as chaperones, play a pivotal role in protecting animals against stress by re-establishing normal protein conformation and, thus, cellular homeostasis. In the last few decades, many advances have been made in ascertaining the HSP response to thermal and non-thermal stressors in poultry. The present review focuses on what is currently known about the HSP response to thermal and non-thermal stressors in poultry and discusses the factors that modulate its induction and regulatory mechanisms. The development of practical strategies to alleviate the detrimental effects of environmental stresses on poultry will benefit from detailed studies that describe the mechanisms of stress resilience and enhance our understanding of the nature of heat shock signalling proteins and gene expression.

Embryonic modulation through thermal manipulation and in ovo feeding to develop heat tolerance in chickens

Healthy chickens are necessary to meet the ever-increasing demand for poultry meat. Birds are subjected to numerous stressful conditions under commercial rearing systems, including variations in the environmental temperature. However, it is difficult to counter the effects of global warming on the livestock industry. High environmental temperature is a stressful condition that has detrimental effects on growth and production performance, resulting in decreased feed intake, retarded growth, compromised gut health, enhanced oxidative stress, and altered immune responses. Traditional approaches include nutritional modification and housing management to mitigate the harmful effects of hot environments. Currently, broiler chickens are more susceptible to heat stress (HS) than layer chickens because of their high muscle mass and metabolic rate. In this review, we explored the possibility of in ovo manipulation to combat HS in broiler chickens. Given their short lifespan from hatching to market age, embryonic life is thought to be one of the critical periods for achieving these objectives. Chicken embryos can be modulated through either temperature treatment or nourishment to improve thermal tolerance during the rearing phase. We first provided a brief overview of the harmful effects of HS on poultry. An in-depth evaluation was then presented for in ovo feeding and thermal manipulation as emerging strategies to combat the negative effects of HS. Finally, we evaluated a combination of the two methods using the available data. Taken together, these investigations suggest that embryonic manipulation has the potential to confer heat resistance in chickens.

Post-Hatch Performance of Broilers Following Hypoxic Exposure During Incubation Under Suboptimal Environmental Temperature

The modern broiler is selected to exploit its full genetic potential, to sustain a rapid growth rate, and to lower the feed conversion rate (FCR). Recently reported reductions in FCR have been associated with augmented tissue formation at the expense of physiological functions such as thermoregulation. In turn, modern broilers exhibit a relatively low capability to balance energy expenditure under suboptimal ambient temperature. Hypoxic conditions at late incubation stages play a role in reforming metabolic plasticity. This work examined the effect of exposure to 12-h hypoxia (12H; 17% O2) for three consecutive days (from E16 through E18), or continuous hypoxia exposure for 48 h (48H), from E16 through E17, as compared to standard incubation (21% O2) on post-hatch performance of broilers maintained under suboptimal ambient temperatures (cold, hot, and diurnal cyclic ambient temperature). 12H chicks kept under hot ambient temperature had significantly lower body temperature (Tb) as compared to the control chicks. On day 42, both 12H and 48H chicks grown in the cyclic temperature room had significantly lower Tbs than controls. In parallel, from week 4, onward, 12H chicks had a significantly lower FCR than controls, and the 48H chicks demonstrated a lower FCR from week 5 and on. 12H and 48H broilers maintained under diurnal cyclic ambient temperature, exhibited significantly greater relative breast muscle weight, and a similar pattern was found in hypoxic broilers raised under standard and hot ambient temperatures. Hypoxic manipulation affects and create an adaptive bias in allocating metabolic energy between maintenance and growth, thus resulting in improved broiler performance, thermoregulation, and rearing under suboptimal environmental temperature.

The Role of Incubation Conditions on the Regulation of Muscle Development and Meat Quality in Poultry

Muscle is the most abundant edible tissue in table poultry, which serves as an important source of high protein for humans. Poultry myofiber originates in the early embryogenic stage, and the overall muscle fiber number is almost determined before hatching. Muscle development in the embryonic stage is critical to the posthatch muscle growth and final meat yield and quality. Incubation conditions including temperature, humidity, oxygen density, ventilation and lighting may substantially affect the number, shape and structure of the muscle fiber, which may produce long-lasting effect on the postnatal muscle growth and meat quality. Suboptimal incubation conditions can induce the onset of myopathies. Early exposure to suitable hatching conditions may modify the muscle histomorphology posthatch and the final muscle mass of the birds by regulating embryonic hormone levels and benefit the muscle cell activity. The elucidation of the muscle development at the embryonic stage would facilitate the modulation of poultry muscle quantity and meat quality. This review starts from the physical and biochemical characteristics of poultry myofiber formation, and brings together recent advances of incubation conditions on satellite cell migration, fiber development and transformation, and subsequent muscle myopathies and other meat quality defects. The underlying molecular and cellular mechanisms for the induced muscle growth and meat quality traits are also discussed. The future studies on the effects of external incubation conditions on the regulation of muscle cell proliferation and meat quality are suggested. This review may broaden our knowledge on the regulation of incubation conditions on poultry muscle development, and provide more informative decisions for hatchery in the selection of hatching parameter for pursuit of more large muscle size and superior meat quality.

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.

Early Phenotype Programming in Birds by Temperature and Nutrition: A Mini-Review

Early development is a critical period during which environmental influences can have a significant impact on the health, welfare, robustness and performance of livestock. In oviparous vertebrates, such as birds, embryonic development takes place entirely in the egg. This allows the effects of environmental cues to be studied directly on the developing embryo. Interestingly, beneficial effects have been identified in several studies, leading to innovative procedures to improve the phenotype of the animals in the long term. In this review, we discuss the effects of early temperature and dietary programming strategies that both show promising results, as well as their potential transgenerational effects. The timing, duration and intensity of these procedures are critical to ensure that they produce beneficial effects without affecting animal survival or final product quality. For example, cyclic increases in egg incubation temperature have been shown to improve temperature tolerance and promote muscular growth in chickens or fatty liver production in mule ducks. In ovo feeding has also been successfully used to enhance digestive tract maturation, optimize chick development and growth, and thus obtain higher quality chicks. In addition, changes in the nutritional availability of methyl donors, for example, was shown to influence offspring phenotype. The molecular mechanisms behind early phenotype programming are still under investigation and are probably epigenetic in nature as shown by recent work in chickens.

Impacts of Embryonic Thermal Programming on the Expression of Genes Involved in Foie gras Production in Mule Ducks

Embryonic thermal programming has been shown to improve foie gras production in overfed mule ducks. However, the mechanisms at the origin of this programming have not yet been characterized. In this study, we investigated the effect of embryonic thermal manipulation (+1°C, 16 h/24 h from embryonic (E) day 13 to E27) on the hepatic expression of genes involved in lipid and carbohydrate metabolisms, stress, cell proliferation and thyroid hormone pathways at the end of thermal manipulation and before and after overfeeding (OF) in mule ducks. Gene expression analyses were performed by classic or high throughput real-time qPCR. First, we confirmed well-known results with strong impact of OF on the expression of genes involved in lipid and carbohydrates metabolisms. Then we observed an impact of OF on the hepatic expression of genes involved in the thyroid pathway, stress and cell proliferation. Only a small number of genes showed modulation of expression related to thermal programming at the time of OF, and only one was also impacted at the end of the thermal manipulation. For the first time, we explored the molecular mechanisms of embryonic thermal programming from the end of heat treatment to the programmed adult phenotype with optimized liver metabolism.

Effect of temperature manipulation during incubation on body weight, plasma parameters, muscle histology, and expression of myogenic genes in breast muscle of embryos and broiler chickens from two commercial strains

1. This study evaluated the effect of a higher incubation temperature on body weight, plasma profile, histology and expression of myogenin (MYOG), insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor A (VEGFA) genes in breast muscle of embryos and broilers from two commercial strains.2. A total of 784 eggs from Ross 308 and Cobb 500 broiler breeder flocks were used. Half of the eggs per strain were incubated at control temperature (37.8°C), whereas the other half were exposed to heat treatment (HT) of 38.8°C between embryonic day (ED) 10 and 14, for 6 h/day. Embryos and chicks were sampled on ED 19 and at hatch. A total of 480, one-day-old chicks per strain and incubation temperature were reared up to 42 d post-hatch.3. The HT increased hatch weight of Ross chicks and 42-d body weight of broilers from both strains. Lower plasma triacylglycerol levels were measured for HT embryos and broilers on ED 19 and 42 d post-hatch, respectively. HT reduced plasma T₃ levels in Ross embryos and broilers for the same periods. Hepatic TBARS concentrations were elevated by HT compared to the control incubation.4. The HT reduced breast muscle VEGFA gene expression of Cobb embryos on ED 19, whereas expression was stimulated in day-old chicks. At 42 d post-hatch, fibre area was increased by HT regardless of strain. Compared to the control incubation, HT increased the breast yield of Ross broilers and leg yield of Cobb. Ross-HT broilers had a higher pH at 24 h after slaughter and better water holding capacity than Cobb-HT broilers.5. These results suggested that HT increased body weight, fibre area, IGF-I gene expression and lowered plasma triacylglycerol levels of broiler chickens from both strains at 42 d. However, HT influenced the expression of VEGF-A and MYOG genes and meat quality differently between the broiler strains.

Embryonic thermal manipulation impacts the postnatal transcriptome response of heat-challenged Japanese quails

BACKGROUND

The thermal-manipulation (TM) during egg incubation is a cyclic exposure to hot or cold temperatures during embryogenesis that is associated to long-lasting effects on growth performance, physiology, metabolism and temperature tolerance in birds. An increase of the incubation temperature of Japanese quail eggs affected the embryonic and post-hatch survival, growth, surface temperatures and blood characteristics potentially related to thermoregulation capacities. To gain new insights in the molecular basis of TM in quails, we investigated by RNA-seq the hypothalamus transcriptome of 35 days-old male and female quails that were treated by TM or not (C, control) during embryogenesis and that were exposed (HC) or not (RT) to a 36 °C heat challenge for 7 h before sampling.

RESULTS

For males, 76, 27, 47 and 0 genes were differentially expressed in the CHC vs. CRT, CRT vs. TMRT, TMHC vs. TMRT and CHC vs. TMHC comparisons, respectively. For females, 17, 0, 342 and 1 genes were differentially expressed within the same respective comparisons. Inter-individual variability of gene expression response was observed particularly when comparing RT and HC female animals. The differential expression of several genes was corroborated by RT-qPCR analysis. Gene Ontology functional analysis of the differentially expressed genes showed a prevalent enrichment of terms related to cellular responses to stimuli and gene expression regulation in both sexes. Gene Ontology terms related to the membrane transport, the endoplasmic reticulum and mitochondrial functions as well as DNA metabolism and repair were also identified in specific comparisons and sexes.

CONCLUSIONS

TM had little to no effect on the regulation of gene expression in the hypothalamus of 35 days-old Japanese quails. However, the consequences of TM on gene expression were revealed by the HC, with sex-specific and common functions altered. The effects of the HC on gene expression were most prominent in TM females with a ~ 20-fold increase of the number of differentially expressed genes, suggesting that TM may enhance the gene response during challenging conditions in female quail hypothalamus. TM may also promote new cellular strategies in females to help coping to the adverse conditions as illustrated by the identification of differentially expressed genes related to the mitochondrial and heat-response functions.

Embryonic thermal manipulation of Japanese quail: effects on embryonic development, hatchability, and post-hatch performance

Embryonic thermal manipulation led to several modifications in molecular, physiological, and biochemical parameters which affect pre- and post-hatch growth performance. The current study aims to elucidate the onset and long-term effects of intermittent thermal manipulations (TM) during two-time windows, early/late, of embryogenesis in Japanese quail (Coturnix japonica) on embryonic development, hatchability, muscle histogenesis, and post-hatch growth performance. Four groups were created; quail eggs in the control group were incubated at 37.7 °C and relative humidity (RH) 55%. Three thermally treated groups were incubated intermittently at 41 °C and 65% RH intermittently (3 h/day): early embryogenesis group (EE) was thermally treated during embryonic days (ED) 6-8, late embryogenesis group (LE) was thermally treated during (ED12-ED14), and early and late embryogenesis group (EL) was thermally manipulated in both time windows. Relative embryo weights in EL and EE were significantly lighter than those in LE and Ctrl groups. The hatched chicks were reared under optimal managemental conditions (three replicates per treatment). Average daily feed intake was recorded, and feed conversion ratio (FCR) was calculated. Histological and quantitative analyses of muscle fibers were performed. The results revealed that TM led to significant hypertrophy of quail breast muscle in (EE). Intermittent short-term (3-6 h) thermal manipulation (39-40 °C) protocols during early embryogenesis (ED6-ED8) could be recommended to enhance muscle mass growth and breast muscle yield in the Japanese quail.

Heat stress and poultry production: impact and amelioration

Globally, the poultry industry is gaining significant importance among the agricultural and its allied sectors. However, heat stress was found to negatively affect the poultry production particularly in the tropical regions. This review is therefore an attempt to generate information pertaining to the impacts of heat stress on poultry production and its amelioration. Heat stress reduces the growth, reproductive performance, and egg production in poultry birds. The reduction in productive potential of poultry birds on exposure to heat stress may be attributed to the deviation of energy resources from production to adaptation pathway. There are different approaches pertaining to relieving the adverse impacts of heat stress on poultry production. These approaches can be broadly categorized under genetic, management, and nutritional strategies. These approaches may reduce the negative effects of heat stress and enhance the productive performance of poultry birds. The management strategies include appropriate shelter design, providing shade, using sprinklers, implementing cooling devices, and using fans and ventilation systems. The recommended floor space for mature birds weighing 1.7 kg is 0.06 m²/bird while it is 0.13 m²/bird for the birds weighing 3.5 kg with 27.8 kg/m² bird density in either case. The nutritional interventions comprise ration balancing and providing essential micronutrients to improve the productive and reproductive performance in poultry birds. Fat, antioxidants, yeast, and electrolyte supplementations are some of the most commonly used nutritional strategies to ensure optimum production in the poultry industry. Furthermore, providing adequate water supply and disease surveillance measures may help to ensure optimum meat and egg production in the birds. The advanced biotechnological tools may aid to identify suitable genetic markers in poultry birds which might help in developing new strains of higher thermo-tolerance by designing suitable breeding program involving marker-assisted selection. These strategies may help to optimize and sustain poultry production in the changing climate scenario.

Effect of incubator tray location on broiler chicken growth performance, carcass part yields, and the meat quality defects wooden breast and white striping

Large variations in hatching egg incubation temperatures have been previously shown to negatively impact posthatch growth in broiler chickens. The objective was to determine whether small incubation temperature variations owing to incubator tray location (LOC) could alter posthatch female and male broiler growth performance and carcass characteristics. Broiler hatching eggs were obtained from a 40-week-old commercial broiler breeder flock and incubated in trays placed in the bottom (BOT), middle (MID), and top (TOP) thirds of the racks (n = 4 racks per incubator tray LOC) in a single-stage incubator in a commercial hatchery. Chicks hatched from the 3 LOC (n = 720 per LOC) were vent sexed, vaccinated, and separate-sex reared with 12 birds per pen in a floor-pen facility and fed a common corn and soybean meal-based diet for 41 d. At day 41, all birds (n = 720) were processed to determine carcass and carcass part yields and incidence and severity of the meat quality defects wooden breast (WB) and white striping (WS). No LOC × Sex interactions were observed (P > 0.05). Growth performance and incidence and severity of WB and WS were similar among LOC (P > 0.05). However, broilers from BOT trays had heavier tender and breast weights than broilers from warmer MID trays (P < 0.05). Broilers from the BOT trays had higher breast meat yield as a proportion of carcass weight (25.00%) than warmer MID (24.54%) broilers (P < 0.05). However, broilers from warmer MID trays had greater carcass yield than those from cooler TOP trays (P < 0.05). As expected, male broilers had heavier carcass, breast, tender, wings, drumsticks and thighs weights and were more severely affected by WB than females (P < 0.05). Overall, these data indicate that the inherent differences in environmental factors among incubation LOC can impact broiler carcass and breast meat yields.

Ontogeny of hepatic metabolism in mule ducks highlights different gene expression profiles between carbohydrate and lipid metabolic pathways

Background

The production of foie gras involves different metabolic pathways in the liver of overfed ducks such as lipid synthesis and carbohydrates catabolism, but the establishment of these pathways has not yet been described with precision during embryogenesis. The early environment can have short- and long-term impacts on the physiology of many animal species and can be used to influence physiological responses that is called programming. This study proposes to describe the basal hepatic metabolism at the level of mRNA in mule duck embryos in order to reveal potential interesting programming windows in the context of foie gras production. To this end, a kinetic study was designed to determine the level of expression of selected genes involved in steatosis-related liver functions throughout embryogenesis.

The livers of 20 mule duck embryos were collected every 4 days from the 12th day of embryogenesis (E12) until 4 days after hatching (D4), and gene expression analysis was performed. The expression levels of 50 mRNAs were quantified for these 7 sampling points and classified into 4 major cellular pathways.

Results

Interestingly, most mRNAs involved in lipid metabolism are overexpressed after hatching (FASN, SCD1, ACOX1), whereas genes implicated in carbohydrate metabolism (HK1, GAPDH, GLUT1) and development (HGF, IGF, FGFR2) are predominantly overexpressed from E12 to E20. Finally, regarding cellular stress, gene expression appears quite stable throughout development, contrasting with strong expression after hatching (CYP2E1, HSBP1, HSP90AA1).

Conclusion

For the first time we described the kinetics of hepatic ontogenesis at mRNA level in mule ducks and highlighted different expression patterns depending on the cellular pathway. These results could be particularly useful in the design of embryonic programming for the production of foie gras.

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.

Characterising the Influence of Genetics on Breast Muscle Myopathies in Broiler Chickens

This report provides the first estimates of the genetic basis of all key breast muscle myopathies (BMM) in broiler chickens [Deep pectoral myopathy, wooden breast, white striping and spaghetti breast] and their relationship with body weight and breast yield. Data from a pure bred high yielding commercial broiler line were analysed to estimate the genetic parameters using a multivariate animal model with the appropriate fixed effects and permanent environmental effect of the dam. Heritabilities of the BMM ranged from 0.04 to 0.25 and the genetic correlation of the BMM with body weight and breast yield ranged from -0.06 to 0.41. Here we highlight that the genetic variance of BMM accounts for a low proportion of the phenotypic variance and the BMM have a low genetic relationship with performance traits. The large contribution of residual variance to the phenotypic variance for the BBM was >71.5% which indicates the importance of the non-genetic effects on BMM. The data presented also show that the moderate to low genetic influence for the development of BMM can be used, through balanced selection, to reduce the myopathy incidence in the long term. The impact of genetic selection against BMM was tested empirically by comparing the incidence of WB and % breast yield of a commercial broiler with a high generation (HG) broiler. The HG broiler used represents 2 years of genetic improvement compared to the commercial broiler; the HG broiler had an 18.4% relative decrease in WB and a 1.02% relative increase in breast yield compared to the commercial broiler. This paper describes the relationship between the genetic and non-genetic factors influencing BMM highlighting the importance of understanding the non-genetic effects on myopathy incidence. It also shows that the genetic component of BMM can be reduced whilst at the same time improving breast yield as part of balanced breeding goals.

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

Myofiber formation is essentially complete at hatch, but myofiber hypertrophy increases posthatch through the assimilation of satellite cell nuclei into myofibers. Satellite cell proliferation and differentiation occur during the early growth phase, which in meat-type poultry terminates at around 8 days posthatch. Thus, any factor that affects the accumulation of satellite cells during late-term embryogenesis or early posthatch will dictate long-term muscle growth. This review will focus on the intimate relationship between thermal conditions during chick embryogenesis and the early posthatch period, and satellite cell myogenesis and pectoralis growth and development. Satellite cells are highly sensitive to temperature changes, particularly when those changes occur during crucial periods of their myogenic activity. Therefore, timing, temperature, and duration of thermal treatments have a great impact on satellite cell activity and fate, affecting muscle development and growth in the long run. Short and mild thermal manipulations during embryogenesis or thermal conditioning in the early posthatch period promote myogenic cell proliferation and differentiation, and have long-term promotive effects on muscle growth. However, chronic heat stress during the first 2 weeks of life has adverse effects on these parameters and may lead to muscle myopathies.

Embryonic thermal manipulation has short and long-term effects on the development and the physiology of the Japanese quail

In vertebrates, the embryonic environment is known to affect the development and the health of individuals. In broiler chickens, the thermal-manipulation (TM) of eggs during the incubation period was shown to improve heat tolerance at slaughter age (35 days of age) in association with several modifications at the molecular, metabolic and physiological levels. However, little is known about the Japanese quail (Coturnix japonica), a closely related avian species widely used as a laboratory animal model and farmed for its meat and eggs. Here we developed and characterized a TM procedure (39.5°C and 65% relative humidity, 12 h/d, from days 0 to 13 of incubation) in quails by analyzing its short and long-term effects on zootechnical, physiological and metabolic parameters. Heat-tolerance was tested by a heat challenge (36°C for 7h) at 35 days of age. TM significantly reduced the hatching rate of the animals and increased mortality during the first four weeks of life. At hatching, TM animals were heavier than controls, but lighter at 25 days of age for both sexes. Thirty-five days after hatching, TM decreased the surface temperature of the shank in females, suggesting a modulation of the blood flow to maintain the internal temperature. TM also increased blood partial pressure and oxygen saturation percentage at 35 days of age in females, suggesting a long-term modulation of the respiration physiology. Quails physiologically responded to the heat challenge, with a modification of several hematologic and metabolic parameters, including an increase in plasma corticosterone concentration. Several physiological parameters such as beak surface temperature and blood sodium concentration revealed that TM birds responded differently to the heat challenge compared to controls. Altogether, this first comprehensive characterization of TM in Japanese quail showed durable effects that may affect the response of TM quails to heat.

Positive Impact of Thermal Manipulation During Embryogenesis on Foie Gras Production in Mule Ducks

Animal studies have shown that very early life events may have programing effects on adult metabolism and health. In this study, we aim, for the first, time to elucidate the effects of embryonic thermal manipulation (TM) on the performance of overfed mule ducks, in particular for the production of foie gras (fatty liver). We designed three embryonic TMs with different protocols for increasing the incubation temperature during the second part of embryogenesis, to determine whether hepatic metabolism could be “programed” to improve its fattening response to overfeeding at the age of three months. Initial results confirm that an increase in the incubation temperature leads to faster development (observed for all treated groups compared to the control group), and a decrease in the body surface temperature at birth. Thereafter, in a very innovative way, we showed that the three TM conditions specifically increased liver weights, as well as liver lipid content after overfeeding compared to the non-TM control group. These results demonstrate that embryonic TM effectively “programs” the metabolic response to the challenge of force-feeding, resulting in increased hepatic steatosis. Finally, our goal of improving foie gras production has been achieved with three different embryonic thermal stimuli, demonstrating the high reproducibility of the method. However, this repeatability was also perceptible in the adverse effects observed on two groups treated with exactly the same cumulative temperature rise leading to a reduction in hatchability (75 and 76% vs. 82% in control), in addition to an increase in the melting rate after cooking. These results suggest that embryonic thermal programing could be an innovative and inexpensive technique for improving foie gras production, although the specific protocol (duration, level or period of temperature increase), remains to be elucidated in order to avoid adverse effects.

Effect of a post-hatch lipopolysaccharide challenge in Turkey poults and ducklings after a primary embryonic heat stress

The effect of embryonic thermal manipulation on the post-hatch immune response to a lipopolysaccharide (LPS) challenge was studied in Pekin ducklings and turkey poults. Commercial duck and turkey eggs were distributed among four treatments: SS-Control (37.5 °C from embryonic day [ED] 1 to 25); SS-LPS (37.5 °C from ED1 to 25 + LPS at D0 [hatch]); HH-LPS (38 °C from ED1 to 25 + LPS at D0; SH-LPS (37.5 °C from ED1 to 10 and 38 °C from ED 11 to 25 + LPS at D0). At ED16 and ED24, the egg shell temperature of the duck and turkey eggs in the HH and SH treatments were higher (P ≤ 0.01) than the SS treatment. Ducklings and poults in the HH treatment had the lowest yolk free body weight at hatch (P ≤ 0.05). At 24, 48, and 72 h post-LPS injection, ducklings and poults in the HH-LPS treatment had significantly reduced BW compared with the SS-Con treatments (P ≤ 0.05). Ducklings and poults in the SH-LPS and HH-LPS treatments had increased plasma heat shock protein 70 (HSP70) and lower splenic HSP70 mRNA amounts than the SS-LPS treatments at 24, and 48 h post-challenge (P ≤ 0.05). At 48 and 72 h, macrophage nitric oxide (NO) production in ducklings and poults in the SH-LPS and HH-LPS treatments was lower than in the SS-LPS treatments (P ≤ 0.05). Ducklings and poults in the SH-LPS treatment had increased thymocyte proliferation compared to the SS-LPS treatment at 24, 48 and 72 h (P ≤ 0.05). At 24 h, ducklings in the SH-LPS treatment had increased splenic IL-10 and reduced IFNγ and IL-6 mRNA abundance. However, both ducklings and poults in the HH-LPS treatment had increased IFNγ, and IL-10 mRNA abundance compared to the SS-LPS treatment (P ≤ 0.05). At 48 h, SH-LPS ducklings and poults had lower splenic IL-10 mRNA abundance (P ≤ 0.05) while the HH-LPS treatment resulted in comparable splenic IL-10 mRNA compared to the SS-LPS treatment (P ≥ 0.05). Ducklings and poults in the SH-LPS treatment had increased thymic and splenic CD8⁺/CD4⁺ ratios at 24 h versus the SS-LPS treatment (P ≤ 0.05). In conclusion, embryonic thermal manipulation from ED11-25 increased extracellular HSP70 release, thymocyte proliferation and IL-10 but decreased splenic HSP70 and IFNγ mRNA amounts at 24 h post-LPS injection. This suggests that mild heat stress during the later stages of incubation could potentially prime the embryonic immune system thereby enhances the immune response as earlier than 24 h to eliminate the inflammatory response without affecting the growth performance by increase the extracellular release of HSP70 in both ducklings and poults. Continuous exposure to the small increase in temperature from ED 1-25 (HH) caused an imbalance between pro (IFNγ)- and anti-inflammatory cytokines(IL-10) which affects hatchling responses to an inflammatory challenge and increased mortality. The amount of extracellular HSP70 could potentially play an important role in modulating the immune response against inflammatory challenges.

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

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

Thermal manipulation of the broilers embryos: expression of muscle markers genes and weights of body and internal organs during embryonic and post-hatch days

Background

In broilers chickens, the molecular bases for promoting muscle development and growth requires further investigation. Therefore, the current study aimed to investigate the effects of daily thermal manipulation (TM) during embryonic days (ED) 12 to 18 on body, carcass and internal organ weights as well as on the expression of muscle growth markers genes during late embryogenesis and post-hatch days. 1500 fertile Cobb eggs were divided into five groups. The first group was a control group and incubated at 37.8°C. The other four groups were thermally manipulated (TM) and exposed to 38.5°C (TM₁), 39°C (TM₂), 39.5°C (TM₃) and 40°C (TM₄) daily for 18 h, respectively, with a relative humidity of 56%. Body weights (BW) from ED 12 to 18 and on post-hatch days 1, 2, 3, 4, 5, 6, 7, 14, 21, 28 and 35 were recorded. mRNA expression levels of muscle growth factor genes (IGF-1 and GH) and muscle marker genes (Myogenic Differentiation Antigen; MyoD), Myogenin, Pax7, and PCNA) during ED 12 to 18 and on post-hatch days 1, 3, 5, 7, 14 were analyzed. On post-hatch day 35, the carcass and internal organ weights have been also evaluated.

Results

TM during certain days of embryogenesis (ED 12 to 18) did not affect the BW of broilers during their embryonic lives. However, TM, particularly TM₁ and TM₂, significantly increased BW, carcass and internal weights of hatched chicks near to the marketing age (post-hatch days 28 and 35). Most of TM protocols induced up-regulation of muscle growth factor genes (IGF-1 and GH) and muscle marker genes (MyoD, Myogenin, Pax7, and PCNA) during embryonic life (ED 12 to 18) and on post-hatch days.

Conclusion

Among the various TM conditions, it seems that,TM₁ and TM₂ induced a significant increase in BW, carcass and internal weights of hatched chicks near to the marketing age. This increase in BW induced presumably via up-regulation of muscle growth factor genes and muscle growth markers genes during embryonic life (ED 12 to 18) and on post-hatch days. Both protocols (TM₁ and TM2) can be used in real-world applications of poultry industry for maximum benefit.

Basal and dynamics mRNA expression of muscular HSP108, HSP90, HSF-1 and HSF-2 in thermally manipulated broilers during embryogenesis

Background

Limited data are available about the kinetics of mRNA expressions of Heat shock proteins (HSPs) and heat shock factors (HSFs) in the thermally manipulated (TM) broiler chicks during acute heat stress. Therefore, this study aimed to investigate effects of thermal manipulation (TM) of broiler chicken during embryonic days (ED) 12–18 on the basal and dynamics mRNA expression of heat shock proteins (HSP108 and HSP90) and heat shock factors (HSF-1 and HSF-2) in the muscle tissue during late embryogenesis, first week of life and during heat stress (HS) on post-hatch days 14 and 28. One thousand and five hundred fertile Ross 315 broiler eggs were randomly allocated to five groups: control group (37.8 °C), TM₁ (38.5 °C for 18 h), TM₂ (39 °C for 18 h), TM₃ (39.5 °C for 18 h) and TM₄ (40 °C for 18 h). Chicks from each treatment group were then randomly sub-divided into two further treatment groups, naïve and thermal challenged (TC). On post-hatch days 14 and 28, thirty chicks from each TC group were subjected to heat stress (41 °C for 6 h), while naïve chicks of each group (n = 30) were kept under regular conditions. The response of chicks to heat stress was investigated by evaluating the change in mRNA expressions of HSP108, HSP90, HSF-1 and HSF-2 in muscle tissue after 1, 3 and 5 h of heat stress.

Results

When compared to the control group, TM resulted in significant increases in the basal mRNA expression of HSPs and HSFs during embryogenesis and altered their dynamic expressions in the muscle tissue after heat stress on post-hatch days 14 and 28.

Conclusion

the current study indicated short- and long-term enhancement of HSPs and HSFs gene expression which was associated with acquisition of improved thermotolerance in thermally manipulated chicks.

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.

Thermal challenge alters the transcriptional profile of the breast muscle in turkey poults

Extremes in temperature represent environmental stressors that impact the well-being and economic value of poultry. As homeotherms, young poultry with immature thermoregulatory systems are especially susceptible to thermal extremes. Genetic variation and differences in gene expression resulting from selection for production traits, likely contribute to thermal stress response. This study was designed to investigate in vivo transcriptional changes in the breast muscle of young turkey poults from an unselected randombred line and one selected for 16 wk body weight under hot and cold thermal challenge. Newly hatched turkey poults were brooded for 3 d at one of 3 temperatures: control (35°C), cold (31°C), or hot (39°C). Samples of the pectoralis major were harvested and subjected to deep RNA sequencing. Significant differential gene expression was observed in both growth-selected and randombred birds at both temperature extremes when compared to control-brooded poults. Growth-selected birds responded to thermal stress through changes in genes predicted to have downstream transcriptional effects and that would result in reduced muscle growth. Slower growing randombred birds responded to thermal stress through modulation of lipid-related genes, suggesting reduction in lipid storage, transport, and synthesis, consistent with changes in energy metabolism required to maintain body temperature.

Effect of thermal manipulation during embryogenesis on the promoter methylation and expression of myogenesis-related genes in duck skeletal muscle

Avian embryos are an ideal system to investigate the effect of incubation temperature on embryonic development, but the characteristics and mechanisms of temperature effects on poultry embryonic myogenesis are unclear. In this study, we investigated the effect of increasing the incubation temperature by 1 °C on the expression of nine myogenesis-related genes in ducks and then explored the correlation between the alteration of promoter methylation and the expression of two of the nine genes under thermal manipulation (TM). The qRT-PCR results showed that TM during embryonic days (ED) 1-10 promoted (P < 0.05) the expression of genes in breast muscle (PAX3, PAX7, MYOG, MCK, SIX1, TNNC1) and leg muscle (MYOD, MYOG, MYF5, MCK, AKIRIN2, TNNC1). TM during ED10-20 promoted the expression of PAX3, MYF5 and MCK and inhibited AKIRIN2 expression in breast muscle (P < 0.05); however, it inhibited the expression of PAX3, PAX7, MYOD, MYOG, MYF5, SIX1, AKIRIN2 and TNNC1 and promoted MCK expression in leg muscle (P < 0.05). TM during ED20-27 inhibited the expression of genes in breast muscle (PAX7) and leg muscle (MYOD, MYOG, MYF5, TNNC1) and promoted MCK expression in breast and leg muscle (P < 0.05). Furthermore, with the Sequenom MassARRAY platform, it was observed that the average methylation level of AKIRIN2 (ED10) and TNNC1 (ED20) in leg muscle decreased (P < 0.05) after TM. Notably, we found significant (P < 0.05) inverse correlations between the methylation and mRNA levels of AKIRIN2 under TM during ED1-10 (r = - 0.969) and ED10-20 (r = - 0.805). Taken together, TM during ED1-10 was more favorable for improving duck myogenesis-related gene expression than TM during ED10-20 and ED20-27. TM during duck embryogenesis seemed to have a greater effect on the development of leg muscle than breast muscle and might alter AKIRIN2 expression by changing its promoter methylation status. These findings may be helpful to understand temperature effects on the muscle development of avian embryos and to explore the role of epigenetic regulation during this process.

Early posthatch thermal stress affects breast muscle development and satellite cell growth and characteristics in broilers

Heat or cold stress, can disrupt well-being and physiological responses in birds. This study aimed to elucidate the effects of continuous heat exposure in the first 2 wk of age on muscle development in broilers, with an emphasis on the pectoralis muscle satellite cell population. Chicks were reared for 13 d under either commercial conditions or a temperature regime that was 5°C higher. Body and muscle weights, as well as absolute muscle growth were lower in heat-exposed chicks from d 6 onward. The number of satellite cells derived from the experimental chicks was higher in the heat-treated group on d 3 but lower on d 8 and 13 compared to controls. This was reflected in a lower number of myonuclei expressing proliferating nuclear cell antigen in cross sections of pectoralis major muscle sampled on d 8. However, a TUNEL assay revealed similar cell survival in both groups. Mean myofiber diameter and distribution were lower in muscle sections sampled on d 8 and 13 in heat-treated versus control group, suggesting that the lower muscle growth is due to changes in muscle hypertrophy. Oil-Red O staining showed a higher number of satellite cells with lipids in the heat-treated compared to the control group on these days. Moreover, lipid deposition was observed in pectoralis muscle cross sections derived from the heat-treated chicks on d 13, whereas the controls barely exhibited any lipid staining. The gene and protein expression levels of CCAAT/enhancer binding protein β in pectoralis muscle from the heat-treated group were significantly higher on d 13 than in controls, while myogenin levels were similar. The results suggest high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active, to chronic heat exposure, leading to impaired myogenicity of the satellite cells and increased fat deposition.

Long-term thermal manipulation in the late incubation period can inhibit breast muscle development by activating endoplasmic reticulum stress in duck (Anasplatyrhynchos domestica)

Poultry embryos are easily affected by environmental changings during incubation, thereinto, the temperature modification is the most important one, but the mechanism of temperature effects on bird eggs is not clear. By using RNA-seq, we have previously found that endoplasmic reticulum stress (ERS) may involve in regulating embryonic muscle development of duck under the influence of temperature alteration. To further clarify the role of ERS in the effect, in the present study, we detected the impact of increasing the incubation temperature by 1℃ during embryonic days 10-27 (E10-27) on the development of duck embryos, and investigated the changes in mRNA and protein expression of ERS marker genes and muscle-related genes under the thermal manipulation (TM). The results of relative weight comparison showed that only the relative weight of breast muscle was steadily decreased by TM from E10 to the first day after hatching (W0). Meanwhile, the real-time PCR and western-blot analysis revealed that raising the incubation temperature stimulated the expression of ERS marker genes in breast muscle at E20. The mRNA expressions of muscle hypertrophy and atrophy-related genes were also detected, and were not changed regularly, however, the protein expressions of hypertrophy-related genes were all decreased at both E20 and W0, and the protein expression of atrophy-related genes were up-regulated at E20. The protein expression of muscle proliferation-related genes were also decreased at E20. Additionally, these results were the same as that in the ERS positive control groups. Taken together, these results indicated that long-term TM during late embryonic period could block the development of duck breast muscle by inhibiting muscle hypertrophy and proliferation, and promoting muscle atrophy at a post-transcriptional level via the activation of ERS.

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.