Light Color Influences Incubation Characteristics, Postnatal Growth, and Stress Physiology with a Lack of Expression Changes of Myf5 and Myf6 Genes in Gerze Native Chicken

Light exposure during incubation can influence hatching characteristics, post-hatch growth, and physiological responses in poultry. This study aimed to evaluate the impact of pre-development exposure to different cold-colored light emitting diode (LED) lights on incubation characteristics, growth performance, stress physiology, and myogenic regulatory factors (MRFs) expression level in the slow-growing native Gerze chicken breed. Fertilized eggs were incubated under red, green, white, or dark conditions. The shortest hatch window was observed under red light (42 h), while the dark condition resulted in the longest (84 h) (<i>p</i> < 0.05). White light exposure reduced hatchability compared to the other groups (<i>p</i> < 0.05), whereas green and red lights enhanced both chick weight at hatch and egg-to-chick conversion efficiency (<i>p</i> < 0.001). Chicks incubated under green light exhibited superior body weight during the first four weeks (<i>p</i> < 0.05), but those from the red light group maintained consistently higher weights thereafter (<i>p</i> < 0.05). The highest serotonin levels were detected in chicks from the dark group, while the lowest were associated with green light exposure. Red light exposure was associated with the lowest corticosterone concentrations (<i>p</i> < 0.05). Gene expression analysis revealed no significant differences in MRFs across groups. In conclusion, the spectral level of light during incubation exerts measurable effects on hatch dynamics, post-hatch growth, and hormonal regulation in Gerze chicken.