I'd be interested in seeing that reading, it not immediately obvious how such a claim could be maintained based on either chemistry or mechanics.I used to bake and reseed egg shells. But I’ve read that the chickens don’t absorb as much calcium from them as the oyster shells. So I don’t do it anymore. I prefer them in my compost for next years soil additive
Oyster shell is calcium carbonate, basically useless for humans, slowly digested in chickens. The slow release is actually a bonus for them, as it continues to provide steady Ca for their use overnight/periods when they aren't eating to support egg shell production over the course of about 25 hours. Eggs shells are ALSO primarily Calcium Carbonate - but which much greater surface area/volume ratio, meaning they dissolve much faster in the chicken's intestinal tract (after being pulverized in the crop), making for a much faster short term "hit" of calcium.
Calcium Citrate, the kind of Calcium we human types can actually make use of (at least, at much better rates than Ca carbonate) is an even quicker Ca boost, sometimes used medically for chickens w/ various egg-related illnesses, like egg binding.
