After so many glowing posts on COTH for TC Senior, I switched my very reactionary six-year-old mare to it and decided I may as well switch all my horses. The mare is doing well. She has never been calm on any other feed and she has stayed level headed with it. My jumper has actually calmed down a bunch, too, which at some point I may decide is TOO calm. We'll see how that goes. But I'm happy with the feed.
The low carb/high fat feed that I think is the best is not actually a feed, but a supplement. It is Buckeye Ultimate Finish 25% fat supplement which comes in a feed-like form. It use it for my TB that is ulcer prone and can no longer have any grain type products. He gets 2 lbs a day with plenty of timothy/alfalfa hay and is doing great. He is also a lot calmer.
I fed all my race horses a pound of all phase ration balancer, smart carb from the Mill of Bel Air and black oil sunflower seeds. It gave them the energy they needed to do their job but helped prevent tying up.