Many behavioral studies and histological analyses of the sense of taste have been conducted in chickens, as it plays an important role in the ingestion of feed. In recent years, various taste receptors have been analyzed, and the functions of fatty acids, umami, and bitter taste receptors in chickens have become clear. In this review, the bitter taste sense in chickens, which is the taste quality by which animals reject poisons, is discussed among a variety of taste qualities. Chickens have taste buds in the palate, the base of the oral cavity, and the root of the tongue. Bitter taste receptors, taste receptor type 2 members 1, 2, and 7 (T2R1, T2R2, and T2R7) are expressed in these tissues. According to functional analyses of bitter taste receptors and behavioral studies, T2R1 and T2R7 are thought to be especially involved in the rejection of bitter compounds in chickens. Furthermore, the antagonists of these two functional bitter taste receptors were also identified, and it is expected that such antagonists will be useful in improving the taste quality of feed materials and poultry drugs that have a bitter taste. Bitter taste receptors are also expressed in extra-oral tissues, and it has been suggested that gastrointestinal bitter taste receptors may be involved in the secretion of gastrointestinal hormones and pathogen defense mechanisms. Thus, bitter taste receptors in chickens are suspected to play major roles in taste sensing and other physiological systems.
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