Over dosing of d3 can cause symptoms similair to mbd. But it depends on the other situations too, like how often and how long he gets sun for? How new is his uvb? What strength is his uvb? What you are gutloading with? Because even though you are dusting if everything else is failing it wouldn't matter. The vitamins such as d3 added to help calcium be metabolized in the dusts, is raw vitamins, which means it is harder for them to draw into their systems and put it to use. Which means a lot less is absorbed than would be if they got it naturally through their food source.