In a review article published in the Journal of Poultry Science, Dr. Phuong V. Tran from the from the Graduate School of Bioresource and Bioenvironmental Science, Kyushu University, Japan, summarizes current understanding of how amino acids, and their metabolites regulate appetite in neonatal chicks.
In the poultry industry, ensuring chicks receive optimal nutrition is paramount, as it influences their early development, health, and long-term productivity. For decades, scientists have tried to unravel the biological mechanisms that control appetite and satiety during the early developmental phases of chicks—a key step toward designing effective feeding strategies. Interestingly, neonatal chicks are an excellent animal model for studying such biomolecular processes in detail. They are a precocial species that begins searching for food immediately after hatching, and their relatively large brains make it easier to administer substances directly into their central nervous system during experiments.
However, despite decades of research, many aspects of appetite regulation in chicks remain poorly understood. Chicks exhibit very short and frequent eating bouts separated by brief resting periods. While appetite is known to be regulated by neuropeptides, these signaling molecules take time to synthesize and act, implying that some other fast-acting signal must be controlling satiety. Could free amino acids, which are rapidly influenced by nutrient uptake, be involved in this process?
Dr. Phuong V. Tran from the Graduate School of Bioresource and Bioenvironmental Science, Kyushu University, Japan, analyzes current knowledge on the regulation of food intake in neonatal chicks in a review article published in Volume 62 of the Journal of Poultry Science on March 15, 2025. The review, titled “Function of Amino Acids and Neuropeptides in Feeding Behavior in Chicks”, focuses specifically on the role of amino acids and their metabolites and how they interact with the appetite-stimulating neuropeptide Y (NPY).
The analysis highlights that short-term refeeding leads to a rapid increase in the concentration of several free amino acids in the chick brain, supporting their role as acute satiety signals. In particular, L-ornithine, which is a metabolite of the amino acid L-arginine, had a potent effect on appetite, inhibiting food intake in a dose-dependent manner. Unlike other appetite-regulating mechanisms, L-ornithine appears to act independently of stress-related pathways.
One of the most critical findings detailed in the review was that, when co-injected with L-ornithine, the strong appetite-stimulating effect of NPY was significantly attenuated. “This implies a potent interaction in the brain between the regulation of food intake by NPY and acute satiety signals by L-ornithine,” remarks Dr. Tran. This interaction suggests that L-ornithine acts as a brake on the NPY-driven urge to eat, providing a fast-acting regulatory loop necessary for the chick’s frequent feeding behavior. The review also examined the roles of other amino acids, such as L-tryptophan and L-proline, noting that their effects on feeding are often tied to their influence on sedation and sleep, which frequently follows a feeding bout in neonates.
The various studies and key findings outlined in this review have implications that bridge basic biology with practical applications. “Knowledge of the key role played by amino acids in the overall network of the central nervous system in neonatal chicks can be used to adjust dietary amino acids for optimal performance in poultry production,” explains Dr. Tran. Simply put, this information can guide the formulation of chick feed to optimize the balance of amino acids, ensuring that chicks receive the best possible nutritional start, thus leading to healthier flocks. Moreover, insights into appetite biology gained using neonatal chicks as an animal model could have parallels in mammals, which are harder to study.
The continued exploration of these mechanisms could not only improve poultry nutrition and productivity but also deepen our understanding of how the brain regulates feeding across species.
