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

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.

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.

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.

Pre-hatching and post-hatching environmental factors related to epigenetic mechanisms in poultry

Epigenetic modifications are phenotypic changes unrelated to the modification of the DNA sequence. These modifications are essential for regulating cellular differentiation and organism development. In this case, epigenetics controls how the animal's genetic potential is used. The main epigenetic mechanisms are microRNA activity, DNA methylation and histone modification. The literature has repeatedly shown that environmental modulation has a significant influence on the regulation of epigenetic mechanisms in poultry. The aim of this review is to give an overview of the current state of the knowledge in poultry epigenetics in terms of issues relevant to overall poultry production and the improvement of the health status in chickens and other poultry species. One of the main differences between birds and mammals is the stage of embryonic development. The bird's embryo develops outside its mother, so an optimal environment of egg incubation before hatching is crucial for development. It is also the moment when many factors influence the activation of epigenetic mechanisms, i.e., incubation temperature, humidity, light, as well as in ovo treatments. Epigenome of the adult birds, might be modulated by: nutrition, supplementation and treatment, as well as modification of the intestinal microbiota. In addition, the activation of epigenetic mechanisms is influenced by pathogens (i.e., pathogenic bacteria, toxins, viruses and fungi) as well as, the maintenance conditions. Farm animal epigenetics is still a big challenge for scientists. This is a research area with many open questions. Modern methods of epigenetic analysis can serve both in the analysis of biological mechanisms and in the research and applied to production system, poultry health and welfare.