Struggle Bus

Oh yes, it's that time of year again where you feel like your not even riding a horse anymore, all you do is ride the struggle bus :/
Well my owes of the current month are this, the big man is just too skinny. Cash, I swear lost probably 150-200 lbs this summer and it shows. He's got to the point where his ribs and points of his hips show. And not the crazy emaciated "Animal Cops" type of deal but it was obvious that the summer was kind of hard on him. I feel like a bad mom sometimes for that.
Last fall he went off of grain because he was too fat, he came off grain and never lost a pound or any ounce of energy! So since last fall he has been off grain and doing very well, until this summer of course.
So about 2 weeks ago, after a nice long weening process back on to grain, he is now on full grain schedule and has decided to remind me what it exactly means to have the power of a hind end motor in a Quarter Horse wit the stamina of a Thoroughbred. So with in the last few weeks my, normally very well behaved, 9 year old Appendix has kind of turned in to a crazy little monster! Well for him at least.
Spooking at the open doors and anything that passes by the viewing room windows, his need to rock bac on his rear end and use it to run down and attack anything that's going faster then him or even a jump.
We need to do something... I mean, I can handle his "crazy-ness" but I don't really want to, and I'm afraid the grain is doing more harm then good. I constantly have to work him down and make him behave and I feel like that's burning more of the grain then he should be keeping to gain some weight.
And I found that the NIHJA circuit that we run has posted next years schedule. First show is in February and I'm hoping to be ready enough to go with our show team. But if we keep going like this and I still am out of a job then that probably isn't going to happen...
I need a job... And some sanity...
Anybody have any weight gain solutions?