Hi and Whinny,
I agree with the previous posts, staying out of the sun during the day with a stall fan, U.V. protective fly sheets(but yeah can get hot in there,go with white)
Supplements. But my question to you is why? Are you showing in hand or confirmation? You said your horse is a Yearling, probably benefits from being out to be a horse , play, grow and learn. My advice if he’s not being shown,is to look to the future of What s best for him in the long run.