All I can add is that I feed timothy/alfalfa cubes to my 25 yr old that is now a hard keeper.
I soak them down into mush because I do not want to tempt choking issues.
I feed straight alfalfa pellets to my coming 27 Arab (also a hard keeper) because one day he decided he wasn't eating the mushy stuff anymore
I wet them right before I put them in his feed pan.
Both these horses also have ulcers, and the amino acids in the alfalfa helps tremendously with their top lines and in preserving what muscle mass they still have
I would be pulling my 17 & 18 year olds out of the tree tops if I fed them even one alfalfa cube
A dry pound of cubes or pellets is equal to a pound of hay.
Between the sweet feed (which everyone on this forum knows how I feel about that:( and the protein in the alfalfa, you might make your horse a little on the "ya-hooey" side
I agree with ditching the sweet feed for a healthier option
As far as feeding alfalfa, you will just have to watch and see if it amps him up; I agree with others that he sure doesn't look like he needs it