Most of the time supplements for box turtles aren’t really necessary. If you’re feeding them a varied diet, they should be getting the nutrients they need from their food, and they don’t need extra.
One exception is calcium. Calcium deficiency can cause death and deformity in turtles, especially hatchlings. Since calcium is so important to turtle health, supplementing this mineral is a good idea. They may also need extra Vitamin D to help them use the calcium.
Reptile Calcium Supplements
The easiest way to give your box turtle extra calcium is to sprinkle powdered reptile calcium on her food before each feeding. To coat live food, like mealworms or crickets, put the insects and a little calcium powder in a bag and shake. Use a calcium powder without extra phophorus.
A piece of cuttlebone in the pen can also add extra calcium to the diet. Having this source of calcium freely available also allows your turtles to self-regulate their calcium intake. This can be especially important for gravid females.
Rep-Cal, Herptivite and Reptivite are all good brands of reptile calcium supplements.
Reptile Vitamin D Supplementation
Just like humans, turtles need Vitamin D to metabolize calcium. They can make this vitamin on their own when their skin is exposed to UVB rays. So if your turtles spend time outside or you use a UV light over their habitat you don’t need to supplement.
If your turtles do not get UVB exposure regularly, it’s a good idea to use a calcium supplement that also contains Vitamin D. You do want to be careful when doing this, because turtles can overdose on Vitamin D.
Reptile Vitamin A Supplements
If your turtle has peeling skin or swollen nictitating membranes, it might have a Vitamin A deficiency. This usually only happens if he is not getting enough plant-based foods. Before resorting to supplements, increase the amount of dark leafy greens and yellow or orange vegetables. Adding a drop of cod liver oil to the food can also help.
Since these same symptoms can be caused by dehydration, too, try increasing the humidity in the habitat and making sure the water bowl is clean and filled.
Only if changing the diet does not work should you consider supplementing with vitamin A,
because it’s very easy to over dose with this vitamin. Too much vitamin A can damage your turtle’s liver, which can lead to problems absorbing calcium.