I tried Impact Pro Performance on a couple of my “medium keepers” last fall. (Eating 3-5 # of grain daily plus free-choice forage, don’t maintain on just ration balancer.) Two were coming off Legends CarbCare Performance, one had been on Triple Crown Senior.
Horse #1, who had been on TC Senior, got sketchy metabolic-looking within weeks, and I fled back to the TC Senior ASAP. There were some complicating factors, so I can’t say for sure it was the feed, but the timing was suspicious.
Horse #2, recent arrival to me, seemed to do equally well on either feed. A year later, she has joined the easy keeper ration balancer-and-muzzle crew. I think she benefited most from good quality forage, which she did not have at her previous barn (according to owner).
Horse #3, history of doing MUCH better on Legends CC Performance than TC Senior for reasons I do not understand, did not do quite as well on Impact Pro as Legends, but the difference was subtle.
I also trialed a few horses on Ultium, and that was a big success. They look better on less feed, and while we joke about the rocket fuel, we saw no change in personality or energy levels. I’d definitely take a second look at that for your harder keepers.