Influence of broiler breeder age on egg characteristics, embryonic development, and early post-hatch physiology

SUMMARYIn modern broiler production systems, maternal factors play crucial roles in shaping progeny performance. Among these factors, breeder age has emerged as a key determinant of progeny development by influencing egg characteristics, embryonic metabolism, and chick physiological quality at hatch. As breeders age, reproductive and physiological changes lead to increases in egg weight, yolk deposition, and follicle size, which are generally associated with heavier chicks at hatch. These changes, however, are accompanied by alterations in eggshell characteristics, including thickness and conductance, which modify gas exchange and water loss during incubation and consequently influence embryonic metabolic dynamics and developmental conditions. Because embryonic development depends on the coordinated interaction between nutrient availability and gas exchange, breeder age also influences the transfer of nutrients, immune components, and antioxidant compounds to the egg, shaping gastrointestinal development, immune competence, and early physiological adaptation. Collectively, these maternal influences determine hatchling quality and the efficiency with which chicks transition from endogenous yolk-derived metabolism to exogenous feed intake, both of which are critical for subsequent broiler performance. Although numerous studies have described individual effects of breeder age on egg characteristics, embryonic development, and progeny performance, the molecular and physiological mechanisms linking these processes remain insufficiently integrated. Therefore, this review aims to consolidate current knowledge on the physiological mechanisms through which breeder age influences egg formation, embryonic development, and subsequent progeny performance, highlighting the mechanistic links between maternal physiology, embryonic development, and early post-hatch adaptation.