Alfalfa, being a legume, is kind of like beans. A small/moderate amount is great, but too much can cause distress. I suspect (but do not know) that the sprouts are fine, though they'd be a bit of a pain to produce. By "fresh", I think green, freshly cut & not dried is likely meant. If an animal, even a ruminant, eats too much fresh alfalfa (as in freshly cut), it could give them a tummy ache and runny poo.I wasn't aware of this! Fresh alfalfa I assume? As in the sprouts rather than the hay?
Rabbits (along with horses) are hind-gut animals. I can't remember all that I read, but you should do a bit of a search. It was interesting and helpful, I thought.