What exercises and workouts can I do with my horse to build up their butt muscles?
Walk up and down hills. Walk over properly spaced ground poles, and eventually raised cavaletti.
Correct riding with a well-fitting saddle.
Hills - done properly
Transitions - done properly
Lateral work - done properly
Pole/cavaletti work - done properly
I say “done properly” because those things can just as easily build the wrong muscling when you allow the horse to pull himself along, neck dropped at the base, back hollow, etc
Work on correct flatwork, a-la dressage, and you’ll build a great hind end.
Hill work and making them use their hind end while working (not long and strung out, but pushing from behind and in a frame—it’s a two-for-one, if you’re doing it right, you’ll also get neck and core muscles!)
I agree. A dressage instructor of mine pointed out that what was effective about the walking over cavaletti was the fact that the horse has no real momentum going that slow, so must use muscle to pick 'em up and put 'em down, as opposed to bouncing through a set at a trot, for instance.
I found that my young horse looked more developed within weeks with this exercise, working up to the cavaletti being set high enough that he had to put a wee bit of effort into lifting his legs deliberately – no strolling through barely lifting his feet.
When we bought our own place, it came with a fairly steep hill, and walking slowly on that – I picture an escalator as we go down – really builds the hind end.