Allie, you mentioned that he is "grained" when you go ride, 5 times a week, but either I missed it or you didn't mention exactly what "grain" he's being fed...okay, never mind, you said a complete feed. You may not be able to control the nutrient level of the hay you get, but if you're buying his grain, you can control that and being fed the proper concentrate 5 days a week should be plenty to get his protein levels up to par. Next time you're out there, look at the nutrient percentage list on the back of your feed bag. With a horse like Ronan, who obviously needs more protein than some other horses, I'd want something that was at least 15% protein....though 18% would be better.
I am a huge advocate for feeding alfalfa to add clean, healthy protein to a horse's diet. Pellets or cubes might be your best option as I'm unsure how easy it is to get good alfalfa hay where you are (I know I can't afford what little bit of crappy alfalfa we've got around here right now).
Something else you might think about doing if the alfalfa pellets/cubes are too expensive or hard to get is getting a lower protein cattle range cube
(make sure of which one you get because cattle feeds can run up to like 40%, which is way
too much for horses). The ones that we get are 20% protein, so I feed them sparingly, mostly as treats, but they are cheap and potent and would safely bring his protein level up when mixed with lower protein feed like hay. Talyn has been reluctant to eat alfalfa, so I've been feeding her about half a pound per day along with her 8-10% protein grass hay to make sure she's getting enough protein to grow properly.
However, I also suggest you have a full workup done by a vet just to ensure that there isn't some underlying cause that needs to be fixed first.