When mine are getting pretty regular natural sunshine time I cut out the D3 completely from their supplement routine. Essentially I just stick to plain calcium, perhaps a multivitamin as well occasionally if it does not contain D3.
Just 20 minutes in natural sunshine produces enough vitamin D in the blood to be detectable 2 weeks later, so in my opinion there aren't any "gaps to fill," as there might be under a waning UVB bulb, for example. It packs a much greater punch.