Systemic effects of heat stress on poultry performances, transcriptomics, epigenetics and metabolomics, along with potential mitigation strategies

Broiler chickens have been genetically selected for higher feed efficiency, faster growth and greater muscle yields to fulfil the global meat demand. These fast-growing broiler chickens produce high metabolic heat, predisposing the birds to heat stress. In addition to the high summer temperatures, increasing global warming is an important concern for poultry production in the tropics. According to the Intergovernmental Panel on Climate Change's 2018 report, global temperature is forecasted to increase at +0.2°C per decade. This temperature rise could pose a significant risk to poultry production. Heat stress leads to excessive production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the body, disrupting the normal physiological state, as well as the growth and development of birds' organs. These ROS/RNS produced due to heat stress alter the underlying cellular mechanisms and transcriptomics. Heat stress interferes with the optimal functioning of various bodily systems, including the digestive, immune, circulatory and neuroendocrine systems. Once the bodily systems are affected, several significant changes are linked directly to transcriptomics, metabolomics and epigenomics. As a result, the performance of poultry is severely compromised. Several mitigation strategies have been explored to develop a cost-effective method to minimise heat stress in commercial chickens; however, the poultry industry is seeking an effective and sustainable approach. Despite the numerous published reviews, there remains a significant gap in comprehending the mechanisms and systemic implications of heat stress. Nevertheless, this gap presents a unique opportunity for researchers and industry to gain a more comprehensive understanding of the impact of heat stress on poultry health and production. This review article aims to elucidate the systemic effect of heat stress on poultry physiology, performances, transcriptomic, epigenetics and metabolomics, along with potential mitigation strategies for the poultry industry.