How to fix horse spine? sorry I can't think of a better way to phrase this question.

I have been working on a horse walk animation for quite awhile now. I am pretty inexperienced with rigging and animation in general, but I am quite familiar and comfortable with Blender as a whole.

Following various image references &amp; video tutorials I have the horse legs working in the way I want.

Edit: Link to armature &amp; keyframes




Now to make Horse really shine, I want to animate his spine bouncing with him. Following this reference image  I can see the stages where his spine should move to certain places, but my rig doesn't transform the way I need it to.

The biggest issue is when I try to make his butt go down, it makes the whole front half of him shoot straight up into space.



I've tried to re-rig it quite a few times, but I am getting the feeling that I am missing something to make it work the way I need. Is it possible I need to use an IK Constraint from the Back to front? I haven't seen anyone use a method like that, but I am very confused on how to approach this problem.
So, considering how your armature is made, you should parent InverseKack and Spine02 to SpineCTRL. At the end, parent SpineCTRL and all the IK controllers and targets to the root bone. Now when you move up and down SpineCTRL, the whole back of your horse follows, as it is supposed to do.