Heat stress (HS) is an important environmental stress factor affecting poultry production on a global scale. With the rise in ambient temperature and increasing effects of global warming, it becomes pertinent to understand the effects of HS on poultry production and the strategies that can be adopted to mitigate its detrimental impacts on the performance, health, welfare, immunity, and survival of birds. Amino acids (AAs) have been increasingly adopted as nutritional modifiers in animals to ameliorate the adverse effects of HS. They are essential for protein synthesis, growth, maintenance, reproduction, immunity, stress response, and whole-body homeostasis. However, HS tends to adversely affect the availability, transport, absorption, and utilization of these AAs. Studies have investigated the provision of these AAs to poultry during HS conditions, and variable findings have been reported. Taurine, L-theanine, and L-citrulline are non-essential amino acids that are increasingly gaining attention as nutritional supplements in HS animals. Similarly, betaine is an amino acid derivative that possesses favorable biological properties which contributes to its role as a functional additive during HS. Of particular note, taurine is negligible in plants, while betaine, L-theanine, and L-citrulline can be found in selected plants. These nutrients are barely found in feed ingredients, but their supply has been shown to elicit important physiological roles including anti-stress effects, anti-oxidative, anti-inflammatory, gut promoting, and immunomodulatory functions. The present review provides information on the use of these nutritionally and physiologically beneficial nutrients as functional additives to poultry diets during HS conditions. Presently, although several studies have reported on the positive effects of these additives in human and murine studies, however, there is limited information regarding their utilization during heat stress in poultry nutrition. Therefore, this review aims to expound on the functional properties of these nutrients, their potentials for HS alleviation, and to stimulate further researches on their biological roles in poultry nutrition.

中文翻译：

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牛磺酸、L-茶氨酸、L-瓜氨酸和甜菜碱在家禽热应激过程中的功能作用

热应激 (HS) 是影响全球范围内家禽生产的重要环境应激因素。随着环境温度的升高和全球变暖的影响越来越大，了解 HS 对家禽生产的影响以及可以采取哪些策略来减轻其对家禽生产性能、健康、福利、免疫力和生存的不利影响变得很重要。鸟类。氨基酸 (AAs) 越来越多地被用作动物的营养调节剂，以减轻 HS 的不利影响。它们对于蛋白质合成、生长、维持、繁殖、免疫、压力反应和全身稳态至关重要。然而，HS 往往会对这些 AA 的可用性、运输、吸收和利用产生不利影响。研究调查了在 HS 条件下向家禽提供这些 AA，并报告了不同的发现。牛磺酸、L-茶氨酸和 L-瓜氨酸是非必需氨基酸，作为 HS 动物的营养补充剂越来越受到关注。同样，甜菜碱是一种氨基酸衍生物，具有良好的生物学特性，这有助于其在 HS 期间作为功能性添加剂发挥作用。特别值得注意的是，牛磺酸在植物中可以忽略不计，而甜菜碱、L-茶氨酸和 L-瓜氨酸可以在选定的植物中找到。这些营养素在饲料成分中几乎没有发现，但它们的供应已显示出重要的生理作用，包括抗应激作用、抗氧化、抗炎、肠道促进和免疫调节功能。本综述提供了有关在 HS 条件下使用这些营养和生理有益的营养素作为家禽日粮功能添加剂的信息。目前，尽管有几项研究报告了这些添加剂在人类和鼠类研究中的积极作用，但是，关于它们在热应激期间在家禽营养中的应用的信息有限。因此，本综述旨在阐述这些营养物质的功能特性及其缓解 HS 的潜力，并促进进一步研究它们在家禽营养中的生物学作用。关于它们在热应激期间在家禽营养中的应用的信息有限。因此，本综述旨在阐述这些营养物质的功能特性及其缓解 HS 的潜力，并促进进一步研究它们在家禽营养中的生物学作用。关于它们在热应激期间在家禽营养中的应用的信息有限。因此，本综述旨在阐述这些营养物质的功能特性及其缓解 HS 的潜力，并促进进一步研究它们在家禽营养中的生物学作用。