ISSUE FOCUS 30 FEED & ADDITIVE MAGAZINE March 2025 “L-tryptophan supplementation in the diet of laying hens is positively related to behavior, reducing aggression, feather pecking and cannibalism; performance parameters, improving feed consumption, egg production and quality; the antioxidant capacity, maximizing antioxidant activity at the cellular and enzymatic level; the balance of the intestinal microbiota, reducing the presence of pathogenic microorganisms.” Tryptophan in corn- and soy-based diets is the third limiting amino acid for laying hens (Bertechini, 2012). Tryptophan is used primarily for protein synthesis in order to maintain egg production, in addition, it has other functions, among which it stands out as a precursor of serotonin. Serotonin is a neurotransmitter that acts on the nervous system and helps to reduce aggression and modulate the stress response through social and environmental adaptability (Martin et al., 2000). In addition, some evaluation results suggest that dietary tryptophan promotes positive effects on antioxidant capacity in fish, laying hens, and rats (Wen et al., 2014; Dong et al., 2012; Raju et al., 2000). Corn, an ingredient present in greater proportion in Brazilian feed, is deficient in tryptophan, containing only 0.06% of digestible tryptophan, while soybeans contain 0.59% (Rostagno et al., 2017). Thus, the combination of ingredients used in the formulation of feed for laying hens may lead to the need to include L-tryptophan, to meet the demand for this amino acid by laying hens. TRYPTOPHAN METABOLISM Tryptophan metabolism occurs in different pathways (Figure 1). Deamination and decarboxylation of tryptophan occurs to form kynurenine in the liver and brain; whereas tryptophan also acts as a precursor for serotonin synthesis in the brain and gastrointestinal tract, this pathway being dependent on the hydroxylation and decarboxylation of tryptophan from the first pathway and the last pathway of tryptophan metabolism occurs through transamination, forming indole-pyruvate (Sallée et al., 2014). More than 90% of tryptophan is metabolized through the kynurenine pathway, in which several functional metabolites related to energy and immune metabolism are produced. (Stone et al., 2013). Nicotinic acid produced from tryptophan in the kynurenine pathway, is essential in the nutrition of monogastric animals and its main function is related to cellular respiration. The energy messengers NADH and NADPH are generated from nicotinic acid which are essential to produce ATP in the respiratory chain. Thus, nicotinic acid deficiency can lead to an energy deficit, compromising the physiological homeostasis of the animal organism and causing its death (Santin et al., 2000). TRYPTOPHAN AND ITS FUNCTIONALITY IN LAYING HENS Dr. Eliane Silva Technical and Sales Coordinator CJ BIO Brazil
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