397 Nutritional requirements related to thermal conditions and modulation muscle and adipocyte development in modern broilers.

Abstract Genetic advances in poultry production have required constant improvements in broiler nutrition. Evaluation of the progress of 40 years of nutritional development in broiler diets demonstrated that different advances in nutrition, such as the use of a metabolizable energy system, ileal digestible amino acids, ideal protein profile, and actualization in requirements, resulted in improvements of 0.55 points in feed conversion, 10% in daily weight gain, and 12.6% in protein deposition, while fat deposition was reduced by 13.3%. However, in environmental conditions with high temperatures, heat stress is responsible for physiological adaptations and changes in energy metabolism, increasing the dependence on lipids as an energy source for birds and reducing protein synthesis, which can modify muscle growth and lead to increased fat deposition. In this context, it is necessary to understand and update the impact of environmental conditions and heat stress on fast-growing genetic lines selected for high muscle performance. The intense genetic selection of modern broilers further exacerbates their susceptibility to thermal stress, requiring updates on the effects of thermal stress on protein and fat metabolism and the assessment of adjustments in nutrient levels and energy-protein ratios in the diet to define the actual nutritional needs of broilers under adverse conditions. This study investigates the interaction between ambient temperature and dietary requirements, with a focus on the roles of energy and protein, particularly amino acids, in optimizing the performance of broilers under varying thermal stress conditions. Using the recommendations from the Brazilian Tables for Poultry and Swine (Rostagno et al., 2024) adapted to the metabolic demands of broilers in tropical and subtropical climates, such as those found in Brazil, we evaluate the mitigation of the effects of high temperatures on performance and muscle and adipose tissue development. The results showed that adjustments in dietary formulations for broiler chickens under thermal stress conditions significantly affected animal performance responses and metabolism, allowing the animals to achieve adequate muscle growth and regular fat deposition, thus ensuring productive efficiency and mitigating the effects of high temperatures. By integrating thermal physiology with nutritional science, this research offers practical insights to optimize broiler diets in regions with high ambient temperatures, contributing to sustainable poultry production systems.