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Abstract
Heat is a major environmental stressor in the poultry industry and results in significant economic loss through reduced weight gain and high mortality. The growth of the Pectoralis major is of great interest in broiler production, and heat stress limits growth of the muscle. To help mitigate the detrimental effects of heat stress on broiler production, research has turned to methionine supplementation, as the essential amino acid plays a significant role in processes affected by heat stress. Additionally, environmental intervention such as thermal conditioning looks to aid broiler production and resistance to heat stress. The general objective of this work is to understand the effect heat stress has on the broiler breast muscle transcriptome and how dietary DL-2-hydroxy-(4-methylthio)butanoic acid (MHA) or DL-methionine (DLM) changes this response. In addition, we seek to understand if and how thermal conditioning affects broiler performance and breast muscle transcriptome. The results of this work show heat stress downregulates the expression of genes related to aerobic respiration and the cellular cycle. When broilers are in the finisher phase of production, heat stress additionally upregulates proteolysis, whereas this catabolic process is unaffected by heat stress in younger broilers. Similarly, the actin cytoskeleton undergoes reorganization when subjected to heat stress at a young age, however older broilers negatively express genes related to the actin cytoskeleton, indicating the cellular structure is less resilient at an older age or when heat stress is prolonged. Though broiler performance under heat stress did not improve with increased dietary inclusion of methionine, the transcriptome reveals above-requirement methionine likely benefits cellular processes, particularly at a younger age. Understanding how a broiler regulates these processes under heat stress and how dietary methionine alters this regulation is crucial in furthering the field of poultry nutrition. Performance and conventional biomarkers may not be sufficient when examining poultry under heat stress, as the transcriptome varies depending on diet and age of the bird.