Your concern regarding the overuse of D3 or any other multivitamins is certainly legitimate. Yes, you can overdose using D3 and vitamins.
The more I keep reading about the problems with the dying dragons’ liver failures, etc. I question the use of vitamin supplementation. How much are these people giving? I worry about that quite a bit. Overuse is worse than underuse.
Overuse can kill, due to the toxic effects. Underuse can kill as well, but usually you’ll see the symptoms of underuse and hopefully be able to correct the deficiency.
Sounds to me like your use of Vitamins and Calcium is pretty much what I do. I use the HerpCare calcium only, and dust with the Rep-Cal and D3 maybe once or twice a week, less with adults, depending on the diet as well.
Calcium in itself isn’t harmful, it is the oversupplementation of the D3 that is harmful. With too much D3 in the system, too much calcium is absorbed, the body gets overloaded and cannot use it all, and what happens is deposition of calcium within the internal organs such as the heart, liver, kidneys, etc. Calcium without too much D3 will just pass through the system without doing any harm.
But who knows exactly how much D3 is too much? I don’t think anyone knows this, if someone did then a strict guideline as to how much should be given would be out there somewhere.
One thing that does concern me though, is the use of the ZooMed lights such as the 5.0 ones. If these lights are really as good as the manufacturer claims and they do allow for the D3 synthesis to take place, then adding extra D3 in the diet may indeed be overdosing the animals.
I know Dr. Fred Frye does warn about excessive D3 use with the Vita-lites. When I have access to natural sunlight for my dragons, I never use any D3 or vitamins. D3 is stored in the liver, and some vets think that it is stored for as long as 3-6 months. I try to supplement as much calcium in the foods that my dragons eat such as the higher calcium/low phosphorous ones.
Mustard greens, collard greens, dandelion greens, turnip greens, just to name a few. Fruits are limited to papaya, mango, raspberries, as most others contain higher phosphorous levels.
I think your supplementation regime is pretty darn good, I certainly wouldn’t change it, unless of course your dragons receive natural sunlight 2-3 times per week during the hours of 11:00-2:00.
Then I wouldn’t give any added D3 in the diet. They would be getting enough from the sunlight exposure. You could add a bit of calcium if you’re concerned about the amounts they are getting, but I think high calcium greens in the diet would almost offset the use of adding calcium, especially for adult dragons.
The younger, rapidly growing dragons probably would benefit from some supplementation, because they do eat more bugs, etc. So they may have an off calcium/phosphorous ratio in their diet.