Beware, this name designates two things: on the stalls (especially in supermarkets), you will find under this name hearts of lettuce, with no real nutritional interest; but sucrine is a variety of lettuce in its own right, that has nice round and crunchy leaves.
Like all lettuces, it should be given in moderation, and only to rabbits already accustomed to greens (high risk of diarrhea otherwise).