THE FATAL TEMPERATURE
WORKSHOP TOPIC - HOW HOT IS TOO HOT & WHAT IS THE FATAL HIGH TEMPERATURE
There are TWO correct answers.
a) The first, and the one which I think is in the mind of those who ask, is that high temperature which kills embryos outright.
That temperature is surprisingly high - 46.5C (see picture below for explanation).
In the DEVELOPMENT stage past about Day14, the embryo can ride through heat spikes.
In addition, it is standard practice in commercial hatcheries to expose Day14 and onward eggs to periods of hot temps, equal to those which they will experience in their destination growing sheds.
b) The second answer is less intuitive.
It is in the first week or so (up to about Day10), while the embryo in the FORMATIVE stage, that even a short-duration spike above 38.8C may cause damage which will not become evident until time for primary pip.
We see some evidence of this early but mild damage as feet, leg and beak abnormalities.
In some cases we see skull damage.
What we do not see, what are not evident are the more serious fatal damage to organs, etc.