My reason for double clutching is as follows. In the wild there are no limitations in this area.
My Masticophis would double clutch every year even when not bred. Twice her eggs went full term (when not bred) and looked just like the eggs shown until I had to cut them open they were way past due and they were clear, Fully calcified but not fertile!
I bred her over a ten year period and found that the amount of supplement determined the quality of the second clutch hatchlings. Her first clutch was always perfect.
On the second clutch babies, without extra supplement, I got full term deformed hatchlings and a few dead in the egg. Once I increased the supplements the survivability of the second clutch increased ten fold.
There are two variables here I have always overdone calcium allowing my mice to chew on pure calcium as much as they wanted, that is why I do not consider un-calcified eggs as non-fertile since my non-fertile eggs go full term.
The second point is that by having a successful second clutch will tax her system and if the supplements do not provide the necessary building blocks to form life I will know and have data that will help all breeders for the long term thus saving countless hundreds of potential hatchlings.
If Indigo were not problematic breeders then and there was no problem in hatching them then my work would be somewhat foolish but if we do not stretch the parameters then how can we gain the valuable information needed to succeed at a more rigorous pace.
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