I've never really understood the whole junior & dwarf thing because surely a dwarf rabbit will still have the nutrition needs of a normal average adult rabbit? I'd be interested in know, but I don't see how a dwarf breed of rabbit would be a different to a larger sized rabbit.
my concern would be that junior food is intended for growing/nursing rabbits so its going to be more fattening. for instance junior food has higher protein and more calories in it for growing rabbits, not an adult that should be at a stable growth/weight now.
the only thing I can think of is that the food is smaller.. but I don't think that would pose that much of an issue imho, and if it does you could break them up. with the likes of burgess theres not much size difference between the junior and adult in my experience.
idk! I'd be worried about feeding a food intended for growing rabbits as the calories and protein, over feeding on protein long term can cause issues such as weight gain & stomach upset. for instance an adult rabbit needs 12-14%, and a growing rabbit needs 16%+. the supreme junior has 17%, burgess has 16%.
I've never fed my mini rexs the 'dwarf' food because I'd be worried about how fattening it is and how much protein is in it compared to what an adult rabbit needs.
if size is an issue (which I don't think it would be) I'd suggest breaking it up.
thats just my own personal opinion tho