I have a coming 3 year old that I think needs a bit more muscle. I like my babies a little on the lean side but especially over his rump he really needs some muscle. The problem is if I give him alfalfa or any feed with alfalfa in it he goes CRAZY. I've been told by nutritionists this can't happen but it does. Every time I try to introduce it he goes from quiet and sweet to almost unhandleable. After he's off it a few days he's back to normal.

Currently he's on 24/7 round bales, California trace plus, Smart Omega 3 and E, redmond daily gold, a small amount of beet pulp, and a little bit of Producer's Pride 12% horse feed because he's a picky eater and that doesn't have alfalfa.

It's so hard to find anything that doesn't have alfalfa. Or a ton of starch and sugar. Help!

Can you get teff grass hay where you are? Teff actually has more protein than alfalfa but absolutely the lowest amount of sugar and starch. I know tractor supply Carries the Teff pellets. Out here in CA we can get teff hay. 

Rice bran is the base of most muscle building supplements, and also my go to for any type of weight gain or bulking up. Its how I get mine looking like body builders.  Its considered a "cool" starch, meaning it shouldn't add energy. I would consider just giving him that, you could even use it to replace the beet pulp. Just make sure its stabilized rice bran, I use the Max E Glo kind myself 

I LOVE teff pellets for my older IR horse but I never realized they had that much protein! I'll have to try giving some to the like guy.

Just looked up the latest numbers and Teff is 12-17% Protein and Alfalfa is 12-14%. SO teff is just a tad higher ! 

The issue of a horse getting hot when alfalfa is added is not exactly what you think. Your round bales are higher in both starch and sugar than the alfalfa that you added in. When alfalfa is fed along with the grass hay it slows the transit time of all the roughage in the hind gut. This means that the grass hay that normally goes through the system fairly fast is slowed down. As a result, that grass hay is more completely digested, including the starch and sugars, and that is what is increasing the blood sugar levels leading to the attitude that you do not like. Switching to Teff is a good idea. Analysis wise, Teff is pretty close to perfect horse hay if put up properly. I live in California, where a lot of horses are only fed alfalfa, and no grass hay at all. Being hot, in general, is no issue at all because the total starch and sugar levels in the diet are low. A grass hay diet with no alfalfa may not lead to a hot horse simply because the grass hay fed alone is not there long, may not be well digested, and the higher starch and sugar level in the grass hay is simply not captured.

Why would it bring a round bale effect the starch and sugar content? We have IR horses fed off the same bales that do fine so it can't be THAT high in starch and sugar.

Its not because its a round bale. Your original post leads us to assume the round bale is grass hay. Most grass hay is higher in starch/sugar than alfalfa. This is why cushings and IR type horses are typically fed alfalfa and not grass. If thats working for you, thats fine. But read Wins portion above again of how when you add alfalfa to a horses diet, its slowing down the metabolism of your forage. Which means since its moving slower through the digestive process, the horse is absorbing more of the sugars and starches than it would just munching the round bale with no alfalfa in the diet. This is whats causing your energy spike, increased absorption of starches/sugars from all sources of your forage because of the slower digestion caused by an alfalfa source. Its not the actual nutritional content of the alfalfa 

Can sweet feeds with alfalfa be the reason for peeps saying alfalfa makes them hot when it's actually the sweet feed with alfalfa? 

My guys are so not hot on the RG/alfalfa diet. The babies play, the show horses get on the muscle a little in the alley, but not one of them is nutty on this feed regime. 

Sweet feed in another issue if fed in amounts over two pounds per day unless you do three or four feedings. The issue there is not protein as the OP asked. The issue is more starch and sugars from a concentrate feed than can be broken down in the small intestine. Once that is overwhelmed, that starch and sugar goes to the hind gut. You could write a book on why that is a bad idea.

It maybe not the protein as much as it's the alfalfa itself. There are some horses that absolutely can't handle it. 

You might add in what you're doing exercsie wise to build that muscle, as that might alter the suggestions being thrown out. More strenuous stuff, you need to think about ingedients for muscle recovery. Protein is just one of many nutrients needed to build muscle. Also, you say a little bit of Producers Pride 12%, keep in mind the analysis on the bag is the calculation for the 4lb minimum feeding rate. Depending on how much you're feeding, your answer might just be more of that if he'll eat it.