Just adding to Peate's comment -- by 'fix the two ends of the curve' one way to do this is use a cluster and rivet to make the ends of the curve follow the closest bone.
As for your Ziva setup, attachment choices and fiber field direction look good to me.
I really think another pass on the animation is required. It's a little hard to get a sense of the performance of the Ziva tissues because the animation is a bit floaty. Without those crisp impacts of the hooves with the ground, you won't see the high frequency jiggle that should propagate through the muscle.
That's really important to get a sense of the weight of the animal.