I have a friend whos daughter runs a super nice 20 year old horse. Very solid & sound. But because hes 20 and ran a lot she put him on summit. The only change that has been done in the last 6 months. about 2-3 weeks after she gave his loading dose he starting being a HUGE handful in the warm up. Kicking like crazy in the stall,  she cant hardly get him in because he has started rearing & lunging in the air with her. Vet checked him, no bleeding, sound & saddle fits good. Im not meaning to start a debate, just curious if anyone has seen this with their horses? You can PM me if you dont want to put it out there. She is taking him back to the vet this week to double check everything. But he went from being so calm and sweet to a complete jerk. Once hes in the arena he works great still.

Eventhough I won't put anything in my horse that is not FDA approved, or manufactured in an FDA approved facility, I can't see where any of the ingredients would cause that but every horse is for sure different. 

I have never used or recommended Summit, but looking at the formula, I can't see that as a cause. Your decription of an onset of negative behavioral issues sounds like ulcers. 

my horse has been on summit for 11 months and it hasn't made him hot. i used it on another horse that i dont have anymore and he wasn't hot either. so idk. that sounds like something else. but idk... anything is possible i suppose lol maybe check with a chiro? maybe feed him slh kidney?

Is it a case of him being hot? Or is it possible that he was extremely stoic, in a huge amount of pain, the Summit got him feeling like a youngster and now he simply feels too good to be cooped up in a stall?

Whats his diet, are they adding supplements ? 

He just finished a treatment for ulcers right after his first episode because it was so strange for him. He is now on a ulcer maintence again. Im not sure what it is but its what she got from the vet. He doesnt get supplement and is on Koolspeed feed. Nothing else has changed for the last 6 months. It may just be a fluke and he has decided he doesnt like being a kids rodeo horse. 

He has always been ready to go in, like on his toes but never bad. He vet checked great when she bought him 7 months ago. So he shouldnt have been in pain

This is what I was going to say, maybe he just feels extra good now. 

Has he always been on Koolspeed? Read the ingredient list. There is not a single volume ingredient that they actually identify. Here is the actual ingredient list in order of use, Roughage Products, Forage Products, Grain products, Molasses Products, Plant proein Products, Processed Grain by-products, Vegetable oil.  At that point they list Lysine which would be added in a very small inclusion, so the above listed products would comprise about 95% of the formula. I have never seen a more vague least cost formulated label than this. This is done so different ingredients can be substituted into the formula to make it for the lowest price depending on what is available for the lowest price in the market when ingredients are purchased for production. Least cost formulated products are likely to be different every time you buy them, and that change may be what your horse reacted to. 

I think they have fed him koolspeed since they bought him. I didnt know that about the feed tho. I have been thinking about feeding it as well. I will look into it more now. Thank you!

There was a time when just about every major company that made equine feed offered a premium line that was fixed formulated. Horses thrive on quality consistant diets. Least cost formulation was reserved for their low price point line where every penny spent on ingredients was pinched to make the lowest retail price possible. Today, very few make "fixed formula" equine rations. You can usually tell the difference by how the ingredients are described on the bag. First, fixed formula ingredients and analysis are printed directly on the bag, since they do not change from one production run to the next. "Least cost" formulas have that information on tear off tags that are attached to the bag. These tags can be reprinted as the formula changes from one production lot to the next. You can't do that when the ingredients are actually printed on the bag instead of on an added tag. In addition, a "fixed formula" will typically have much clearer descriptions of the ingredients that are easy to understand. Terms like "forage by-products, roughage by-products, or any "by-product" term is intentionally vague to give the manufacturer room to substitute just about anything in the formula. If they used the same "by-product" every time, why not just  say what that is. But, they don't. That is why they use these vague terms to discribe the ingredients in the bag.  Don't be fooled on this. It makes a real difference in your horses health.