She went after them, not just in a dominating way but with her front hooves pounding at them like she was going to smash them to bits, like she hated them the way a donkey hates a coyote!
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At first I tried yelling "NO" and hit something loud (a bucket onto a tree stump) to startle everyone into reality. That didn't 'work' per-say, but it did slow things down. Then I ran to my house, cut up carrots and used the reward method. I had JuJu walk past the chickens over and over while giving her treats, and if she made a move towards them I touched her chest and said a firm "NO". That seemed to calm things down for a little while.