Calcium! That deserves a little more research. First time that's came up in this discussion. Thanks Tom and thank your wife for me. Interesting stuff.View attachment 375371
Just adding to the conversation here. Forgive me if I get the details wrong. My microbiologist wife just explained it to me again, so here goes: This is a "gastric enterolith". It was surgically removed from her horse's stomach. The vet explained that the horses ingest some sand while eating their food off the ground, the sand clumps in the gut for whatever reason, and then the calcium from high calcium foods like alfalfa binds to the sand, forming calcium oxalate, which is what this "stone" is made of. I do not understand how this is possible, and why bale after bale of hay was able to pass on through the GI tract while this thing was in there growing larger the whole time, but there is it. Cost me $10,000 to learn to not let a horse eat off the ground, and to give them supplements that will make any accidentally ingested sand pass through the gut.
So when someone asks questions like: Why does the sand collect in the tortoise's gut when other things pass through, or how is sand worse than other substrates in this regard, or how does sand clump up and become like cement in the gut? I do not know the technical answers to those questions. I do know that there are processes taking place that we don't understand or even know about. I do know that some tortoises get impacted when sand is ingested, and some tortoises are able to pass some sand at least some of the time. I do know that adding sand to a tortoise enclosure could lead to impaction, though it doesn't lead to impaction 100% of the time. I do know that if there is no sand added, then there is no sand impaction 100% of the time.
Here is another possible factor: I have read that plants grown in areas with sandy soil and heavy annual rainfall, like the south eastern US, tend to have less calcium than plants grown in more fertile calcium rich soils like here in CA. In fact, so I've been told, some people add calcium to their soils in the south to add more calcium to the plants they are growing. I don't know if this is a factor in sand impaction or not, but the guys arguing that sand is not an issue are both in the eastern US with heavy rainfall and sandy soil, while the guy who has seen lots of sand impaction cases is in a desert basin with very low annual rainfall and calcium rich soil.