its not on the list of things that rats should absolutely not have but it would definately be on the list of occasional treats. alfalfa is not easily digested by rats so just about all of it is junk food. my understanding is that in small quanties and only as the occasional treat they should be fine but as part of a regular diet, well its just giving them more reason to poop and that's about it.
Does this go for all sprouts? I give my rats a little clover sprout every day and they love it and I know my local grocery sells several kinds of sprouts so just wondering if you meant specifically alfalfa or all sprouts.