Nucleotides as conditionally essential nutrients for optimal health, performance, and product quality in laying hens: a concise review

Intensive chicken egg production is characterized by several stressors that negatively affect bird welfare, productivity, and product quality. Whereas antibiotic growth promoters (AGP) are used to mitigate these stress-induced maladies in poultry, their role as primary drivers of antimicrobial resistance in human and animal pathogens has seen calls to ban or restrict their use. However, withdrawing AGP without reliable alternatives could result in gut dysbiosis, high morbidity and mortality rates, and poor bird performance. This is particularly true in the Global South, where infectious disease burdens increase. Dietary nucleotides (NT) are touted as potential AGP alternatives that enhance gut functionality and immune responses in birds and other animals. Their increasing popularity lies in their critical role in cell growth, development, and repair, which, in theory, can improve growth, immune function, and disease resistance in stressed poultry. Under normal conditions, de novo synthesis and salvage pathways meet an animal's NT requirements. However, during periods of intestinal injury, rapid growth, stress, or inadequate protein intake, the body's demand for NTs may exceed endogenous supply, necessitating exogenous supplementation. Thus, well-timed NT supplements could positively modulate gut morphology and microbiota, enhance feed intake and nutrient utilization, and reduce bird stress biomarkers. However, studies that evaluate the impact of NTs on laying hens and their eggs are not only limited in number but also present inconsistent findings. In addition, the mechanisms of action of NTs in poultry are not yet fully understood. Accordingly, this review consolidates current evidence on the physiological roles and mechanisms of action of NTs in poultry, highlights the limited but emerging data in laying hens, and identifies key knowledge gaps that must be addressed to inform future research and practical implementation for sustainable egg production.