I asked our vet the same thing regarding hen eggs.
Didn't really give a definite answer. Seemed to say that 1 or 2 each week was fine for a treat but that they didn't really need anything except their complete dog food. His concern seemed to be that they would add to the overall calorie intake and that Labradors put weight on easily so that would be his reason for limiting number given.
Ours have quite a few each week at certain times of the year but I'm careful about their weights so doesn't seem to be a problem yet .... they get loads of exercise and I'm careful about portions. In fact our Flattie has always had trouble maintaining weight. He is a bit hyper though.

Interested to see what others have been advised.