Temperature during the last week of incubation. III. Effects on chicken embryo physiology

We investigated effects of eggshell temperature (EST) of 35.6, 36.7, 37.8, or 38.9 degrees C applied from d of incubation (E) 15, E17, or E19 onward on chicken embryo physiology. A total of 2,850 first-grade eggs of a 43-week-old Ross 308 broiler breeder flock were incubated at an EST of 37.8 degrees C until E15. From E15, E17, or E19 onward, eggs were incubated at an EST of 35.6, 36.7, 37.8, or 38.9 degrees C. Plasma glucose, uric acid, and lactate concentrations, and hepatic glycogen amount and concentration were measured at E15, E17, E19, internal pipping (IP), external pipping (EP), and hatch. An EST of 38.9 degrees C applied from E15 onward decreased the amount of hepatic glycogen from E19 to IP and resulted in a lower glycogen amount at IP compared to all other EST. At EP, when oxygen (O-2) becomes largely available, an EST of 38.9 C resulted in a higher glycogen amount and concentration compared to IP, which suggests that plasma glucose between IP and EP might be used for building up hepatic glycogen reserves. However, hepatic glycogen levels remained considerably lower at IP, EP, and hatch at an EST of 38.9 degrees C, compared to an EST of 35.6 and 36.7 degrees C. Opposite to an EST of 38.9 degrees C, from IP onward, an EST of 35.6 C resulted in a higher glycogen amount and concentration compared to all other EST, which might be caused by the higher O-2 availability relative to the lower metabolic rate, which provided time to build up glycogen stores from excessive glucose. A higher availability of hepatic glycogen might contribute to an improved physiological status of the broiler chicken embryo toward hatch. Hepatic gluconeogenesis is crucial for developing embryos, as glucose is the major energy source from IP until hatch. At hatch, no effect of EST was found for glucose, uric acid, or lactate. Results of this study emphasize that EST of 35.6 and 36.7 degrees C from E15 onward appear to be beneficial for chicken embryo physiology.