If I was fattening a horse I would probably use barley (as well as the hay) as it won’t make them hot, but it does need cooking. I would mix it with chaff and bran, further than that I need to brush up on my horse nutrition as there has been a lot of advances in the past few years.
He is a thoroughbred. They can be very calm and well-mannered right up until they are not. They are not bred to be placid schoolmaster types, it is just that they are versatile enough to be. IMO they are not suitable for beginners or nervous riders, and yes I know some people here will shout me down on that, and some riding schools use them…yadda yadda.
I have to disagree with this. Barley is an actual grain, like corn and has a high NSC content of 57%. Corn and Barley are not digested in the large intestine, and can cause ulcers if too much is fed.
Having known many Thoroughbreds, yes there are a few that are actually not hot whatsoever, can babysit little kids, never get worked up at all. I have ridden Thoroughbreds that you could not get to move out if you lit a firecracker under their tail. I have to disagree with the bias that all TBs have an innate reactive or hot side. Some are more calm than the calmest QH. Some of these even have come off the track, but typically were only started one time and cantered around behind the rest of the field before flunking out of racing.
You have known this horse for six years...the past three the horse was not in work. Have you ever known the horse when he was at a good weight, had good hoof care, and was not in pain? I've known some horses that were rather dull until getting very healthy, and then they became more energetic. BUT you have to realize if this happens that it is not about what you are doing wrong, but what you are doing RIGHT. If this is the case, it's great for the horse even if he needs to go to a home with someone who can deal with that energy level.