I don't know specifically about alfalfa, but I find that oats (and oat related feeds like sweet feed) do. My showjumper was put on it when he first started out and he's constantly got energy
I don’t know if there is a truth or myth, but all the truth are in the composition and in the characteristics. Variability of nutritional content can be high in oats, for example the starch content can range from 32% all the way up to 43%! Oats are all natural and a whole grain that is closest to the horse's natural diet. Oats are also free of additives, extra sugars and do not contain GMOs (genetically modified organisms). Horses fed oats eat slower and chew more, which stimulates saliva and good digestion. It’s the same thing for alfalfa, the digestibility of the alfalfa is good and does not need to be processed to have a high level digestion. Horse owners need to make sure they feed what is needed to meet a horse's calorie requirements.