Hips

We're going to animate the hips now to loosen the gallop up as it looks extremely stiff at the moment. Notice the double-ended arrow controls on top of the horse's body. Select the rear end one called "ct_rearTorso_CTRL".

To make things simple we're only going to just animate the Rotate X. At Frame15 Rotate X forward to about 9, as here all it's weight is being supported by the one hoof onthe ground so the hips need to lean forward for balance. Then at Frame 6 Rotate X back to -8, as here it's being supported by it's back left leg so it needs to lean back a little.

At Frame 12, both back legs are stretching high out in the air and the horse is being supported by it's front left leg. We'll need to rotate the hips forward to about 15, this will raise the legs higher and let the hips lean closer to the supporting hoof. 

After framing te key poses, we'll once again clean up the curve. Start by shifting Frame1 and Frame 16 up above the axis. We can probably delete Frame as it isn't needed now. 

After we've adjusted the tangents your curve should look something like this, where the hips rotate forward slightly faster than rotating back.