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The influence of a reduced oxygen content (15% O2) in incubation air on the blood gas status in the chorioallantoic vein and morphological parameters were examined. Furthermore the correlation between reduced oxygen content and age of embryos was determined.
Eggs from white leghorn hens were incubated with a temperature of 37.5°C and at a relative humidity of 60% . Eggs were divided into 3 groups. The first group served as a control was incubated with 21% O2 during the entire incubation period. The first experimental group (V1) was incubated with 15% O2 from day 6 (D6) to D12 and with 21% O2 during the rest of the incubation period. The second experimental group (V2) was incubated at 21% O2 from D1-D12 and at 15% O2 from D12 until samples were taken. Blood probes were taken on D14, D16 and D18 and measured as quickly as possible in ABLTM500 Blood-Gas-System (Radiometer Copenhagen). Body and heart masses of embryos were also obtained as results.
The relative body masses of embryos increased from about 10% on D14 up to 33% on D18. These results comply with literature data (FREEMAN und VINCE, 1974; ROMANOFF, 1960). A reduced oxygen level of 15% in the incubation air from D6 to D12 is expressed in a tendency to higher body masses on experiment days. It can be concluded that these embryos have adapted to a lower oxygen content, which in turn leads to an increased ability to use the re-normalised oxygen level of 21% more efficiently. A reduced oxygen level in the incubation air from D12 to the day of the experiment (D14, D16 or D18) leads to significantly reduced embryonic masses on days D16 and D18.
The mean values of relative heart masses were between 0.8% and 0.97% for this time period in all three groups.
The embryonic heart is more resistant against oxygen deficiency than the adult heart. It has a lower energy demand and is largely able to provide this by anaerobic glygolysis (OSTADAL et al., 1999).
A reduced oxygen content from D6 until D12 expresses itself in a tendency towards higher values in measurements of pO2 and SO2.These results confirm the statements made in other studies, which describe this period as so-called “critical window” concerning the ability for adaptation.
Embryos that were incubated at 15% oxygen during a later period of incubation (from D12 until the gathering of sampled) were also able to react to it. In this group, a lower level of body mass leads to a reduction in oxygen demand, as this rises in proportion to the body mass. A reduced oxygen saturation combined with a pO2 at the same level as the control group means a shift of the oxygen dissociation curve to the right.
The affinity of hemoglobin for oxygen is reduced and, thus, more oxygen can emter the metabolism.
The chicken embryo is able to react to changes in its environment by several regulatory mechanisms and adaptation processes and, thus, to secure its survival in this altered environment.
The results of this study contribute to the further characterization of the capability of the embryo to react to oxygen deficiency in different periods of development.