Supplements for younger horse (OTTB)?

After having retired my older OTTB, a younger version arrived yesterday. I'm used to feeding a whole bunch of different supplements. Starship, was on glucosamine, chondroitin, MSN, coat shiners, electrolites, aspirin, etc, etc.
Tex is only 5 and needs to gain some weight and grow some muscles. I gave him alfalfa yesterday, which he loves, but he used to only get bermuda, so I'll be switching to mix when this bale is gone.
However he did not touch his pellets, did not eat one, it had wheat germ oil on it, so maybe that's what he does not like, but it is strange to me that a horse does not like pellets.
I'm trying to find out what he was fed when he was in training, someone should know what he likes.
Does anyone have experience with young OTTB's and what he may like that will make him somewhat heavier and will built his muscles (he's been out on the pasture for the last 8 months, so we'll build up exercise slowly), but doesn't turn up the nervousness level? He's so nice and calm right now.

Dont buy lots of supplements. If all he needs is weight give him more hay...
For pellets- I've seen this in my weanling as well. He never ate pellete, so he wouldnt touch them at first. He would only eat sweet feed. We gradually mixed it so he switched to pellets w/o a problem. Don't mix alot of stuff in his food he's not used to. I would let him chill out a little, and try very hard to find out what he was on before. Track horses are usually on a performance mix, sweet feed or COB (corn oats barley)

I also have an OTTB, he's only 11 which is decent for a horse but he was on the track for almost a decade. I guess depending on how many races your guy saw, I would keep up with the MSM and glucosamine (I personally use a joint supplement with HA), and maaaaybe with the coat supplements. I used Super 14 to keep a layer of sub-QT fat on my boy, and it seemed to work pretty well without giving him a belly.

Maybe try soaking his feed pellets, if they are soakable, to make more of a mash? You would of course have to use the powdered form of supplements, but those are often a few dollars cheaper than their pelleted counterparts. Its