Interesting. My local TSC has both and charges an extra $1.00 per 50 pound bag for the Purina. I don't know if there is any difference in formulation or not. If there is, it might show up on the contents label. I'll stick with Dumor anyway. From my seven pullets the last three days I've gotten 7, 6, and 6 eggs. I don't think the extra buck a bag would improve that much.
I was told by two workers at my local TSC that Purina and Dumor are packaged at the same company. I have been buying the Dumor because its a little cheaper. It used to be more.... till they recently started carrying Purina a few months ago.