Synergistic Effect of Variable Temperature and Red LED Lighting During Incubation on the Growth and Metabolism of Chicken Embryos and the Quality of Day-Old Egg-Cross Chickens

The effect of variable temperature, red LED lighting, and their combination applied during egg incubation on the growth of chicken embryos, development of their visceral organs, and metabolism, as well as on the quality of day-old chickens, have been studied. Eggs of the Lohmann Brown cross (n = 600) were incubated for 21 days using an ILB-0.5 hatcher. Three incubation regimes were used: VT, incubation at variable temperatures in the dark (37.8°C for the first 14 days, 39.5°C for 2 h per day on days 15–17, 37.5°C on day 18, 37.0°C on days 19–21; RH 57.0%); CL, constant red LED lighting at the standard incubation temperature (37.6 ± 0.1°C) and RH 55.0%; and VT+CL, incubation at variable temperatures with the constant red LED lighting. Using morphometric methods, the height and weight parameters of chicken embryos, the state of their visceral organs (heart, gizzard, liver, spleen), and the body length and weight of day-old chickens were assessed. The heart rate, respiration rate (by CO2 release), and heat production in chicken embryos were evaluated using the scaling method. To the hatching period (day 19), the VT+CL regime was shown to decrease the embryo body weight by 3.464 g compared to the CL regime and the spleen weight by 0.005 g compared to the VT regime but to optimize the metabolic rate evaluated via the CO2 release by 21.42 and 47.20 mL/h, respectively. On day 19 of incubation, the heart rate and the heat production of chicken embryos slightly varied without clear difference. Compared to the VT variant, the effect of the combined VT+CL variant was manifested through an increase in the body weight of chickens by 1.93 g. The proposed neuroendocrinal mechanisms regulating the growth, metabolism, immune response, thermoregulation, and stress responses of chicken embryos based on the synergistic VT+CL effect have been presented in the form of a flowchart.