Originally Posted by A knack for horses
I'd say you should pump up his feed. Yearlings are at a stage where they grow like weeds. Their bodies are transitioning from the foal stage to maturing into a full grown horse, so he may be growing up faster than he can fill out.
My best advice would be to give him some extra feed to help compensate for his growth. I'm pretty sure if you feed him some extra hay he'll start to fill out more.
And I know you didn't ask about it, but are you planning on gelding him? It'll be a lot easier to keep and handle him once he reaches maturity, and if you want to re-home him, I think more people are willing to accept taking in a gelding rather than a stallion.
yes, do plan on gelding him especially since he isn't papered. We have another colt we rescued with him that has grown great and is filled out very nicely and muscled up. Ghost, the little troubled one, hasn't grown much and honestly has dropped his muscle mass is seems. We havehad over month of 100+ weather here so I know that's not helping any! He doesn't seem to be uncomfortable but he sure doesn't look good