ISSUE FOCUS FEED & ADDITIVE MAGAZINE March 2025 31 TRYPTOPHAN AND ITS FUNCTIONALITY Tryptophan, also known as α-amino-β-indolepropionic acid, it is involved in several physiological functions (Le Floc’h et al., 2011). This amino acid is essential for birds, fish and mammals (Wu et al., 2014) as it is not synthesized in these animals, therefore tryptophan must be supplied through diet. Tryptophan is also considered a functional amino acid, simultaneously with other amino acids such as arginine, cysteine, methionine, which regulate important metabolic pathways to improve health, survival, growth, development and the reproductive process in animals (Wu, 2020). Tryptophan and its metabolites are also involved in immune intestinal homeostasis (Gao et al., 2018). In addition to improving feed intake in poultry, it contributes to improving production performance and helps in the synthesis of hormone-binding substances (Sarsour et al., 2021; Khattak & Helmbrecht, 2019; Ducy & Karsenty, 2010; Le Floc’h et al., 2008). Tryptophan is also crucial for different metabolic and physiological activities in the animals as synthesis of neurotransmitters and vitamin B3. It shows positive effects on the balance of the intestinal microbiota, on enzymatic and non-enzymatic antioxidant capacities. Tryptophan has a positive effect on behavior animal by stimulating serotonin secretion; on immune modulation (Khattak et al., 2019; Bello et al. 2018; Bai et al., 2014; Wen et al., 2014; De Ponti et al., 2007; Tirapegui, 2004). EFFECT OF TRYPTOPHAN ON ANIMAL BEHAVIOR Tryptophan is able to modulate the behavioral aspects of laying hens, especially by reducing feather pecking, which is considered an initial factor to cause injuries and, consequently, cannibalism and death of the birds (Birkl et al., 2019; Van Krimpen et al., 2005; Van Hierden et al., 2004). The behavioral modulation exerted by tryptophan reflects positively on animal welfare. This effect occurs through serotonin which is involved in several physiological functions such as regulation of body temperature, food intake, sexual behavior, response to stimuli that cause fear, fight and stress behavior (Lucki, 1998). From 1 to 2% of the body's serotonin is produced in the serotonergic pathway in neurons in the brain, while approximately 95% of serotonin is produced, stored and released by cells in the intestinal mucosa known as enterochromaffin cells (Gershon & Tack, 2007). Protein synthesis Tryptophan Kynurenine 3-hydroxy anthranilic acid Picolinic acid Xanthurenic acid Quinolinic acid Niacin CO2 3-hydroxykynurenine 5-hydroxy-tryptophan Serotonin Figure 1. Tryptophan metabolic pathways (Adapted from Le’Floch & Seve, 2007)
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