There are three issues here.
-One is calcium oxalate crystals - raphides - which are listed as "toxic", causing irritation and swelling of the tongue, esophagus, etc.
-The second is the pressence of oxalates that then binds with calcium and limits calcium availability.
-The third is too much oxalic acid can bind with calcium in the urinary system and leads to stones or uroliths.
I agree - most all we hear is based on heresay and information taken from studies/issues with other animals and is not based on studies or facts about the way chelonians process foods.
raphides are indeed of concern with mammals. Plants have evolved this mechanism as a way it seems to make themselves unpalatable and not get eaten. For mammals, this does indeed result in swelling and irritation and worse. However, there is absolutely no cases of any chelonian ever being affected by raphides. Just as they can devour a prickly pear pad loaded with glocids or a thistle that I cannot handle without gloves, raphides also are of no effect.
Oxalates do indeed bind with calcium. However, the issues should be how much free calcium is still available even with some bound by the creation of calcium oxalate? As William @Kapidolo Farms has pointed out in several posts and his talk at TTPG - many of the "forbidden plants" have good levels of calcium even after considering the binding of some with the oxalates. It seems the overall ratios in the diet just as with phosphates, is the key concern here.
That then leads to the warning of urolith formation or stones. Again in mammals, that is a concern and can be a cause of kidney stones with the formation of calcium oxalate uroliths. However, the assumption that the same happens in chelonians is not borne out by actual science. If fact in a very compreshensive study of any urolith and veterinarian would send them, it was found that absoluted none of the uroliths found in chelonians creating a "stone problem" contained any concreation of any form of calcium. It is purine based stones that can cause problems with chelonians and has nothing to do with calcium or therefore oxalates binding with calcium. So it is the processing of excess proteins in the diet, not calcium binding, that creates all know cases of stone issues that have indeed been tested and verified.
Lots of well stated information in this Post - thank you.
