Abstract

In the first experiment, eggshell temperature (ET) in the control group was kept constant at 37.8°C, and embryos in the experimental group were exposed to varying ET within the range of 36.8 to 38.8°C using ET steps of 0.2°C and time steps of 3 h.

This was repeated in 3 periods between 6.5 and 9.5 d, 10.5 and 13.5 d, and 14.5 and 17.5 d. In the studied ET range, heat production (HP) increased linearly at 4.9% per 1°C ET. In the second experiment, a standard machine temperature (MT) was used for the control group, and eggs in the experimental group were exposed to low (MT - 0.3°C) or high (MT + 0.3°C) temperatures for 1 h of time at d 8, 9, and 11 to 16.

When MT was decreased, CO₂ production initially increased at 0.5% and decreased thereafter. When MT was increased, CO₂ production initially decreased at 0.4% and increased thereafter. It was concluded that embryonic HP responded linearly with short-term ET changes in the studied ET range of 36.8 to 38.8°C. Changes in CO₂ concentration due to short-term MT changes could not be explained by embryonic HP only. It can be speculated that blood flow through the chorio-allantoic membrane changes with MT, affecting heat transfer and diffusion of CO₂. A second, delayed response to MT changes was in accordance with the findings in Experiment 1.

Within the studied temperature range it will be difficult to use embryonic metabolic responses as a tool to control the incubation process. Because HP is linearly related to ET as in the studied temperature range, other factors such as O₂ availability or CO₂ release may limit embryo development at higher ET. At this moment, research on the effects of gas exchange at different temperatures on embryo development and survival is lacking.

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June 2006