Changes in albumen pH due to higher CO2 concentrations during the first ten days of incubation

Recent results have shown that hypercapnia during early stages of embryonic development alters several parameters related to embryonic growth and hatching. In these experiments, we wanted to investigate how external CO2 concentrations in the incubator can be sensed by the internal environment of the egg itself. Cobb eggs of a flock of 37 weeks of age were used for incubation under different CO2 patterns during the first ten days. CO2 concentrations were automatically controlled in such way that CO2 gradually increased to 1.5 % at ED10. After day 10, these eggs were further incubated under standard conditions. Control eggs were incubated throughout the experiment under standard conditions. The pCO2 in the air chamber was consistently higher from day 2 onwards. After an initial rise in albumen pH in both groups, pH showed a steeper decrease in the eggs of the CO2 group, with significant lower values at days 2, 6, 7, 8 and 10 of incubation. Embryo weights were significantly higher from ED7 onwards which was combined with a shift forward in the hatching curve, the CO2 chicks hatching earlier than the chicks incubated under standard conditions during the first ten days. Hatchability was comparable in both groups. To further explore this effect of CO2 on these parameters, a second experiment was performed following a steeper CO2 curve during the first ten days (Cobb eggs, age of flock : 31 weeks). CO2 levels increased from day 4 until day 7 to reach 2 % which was continued until day 10. In line with the previous experiment, albumen pH was influenced in eggs incubated under higher CO2, being significantly lower at days 6, 7, 9 and 10 compared to control eggs. Embryos tolerated well this level of CO2 and again showed significantly higher weights at several incubation days combined with a shift forward in the hatching curve. In conclusion, these results show that the gaseous environment of the incubating egg clearly influences pH of the albumen. It remains to be investigated how these pH changes, which are known to be important in embryonic developmental processes, can be linked with the changed embryonic growth and timing of hatching.