I know darn near nothing about horses. This, and Google fu provided some interesting reading. How often does this become a problem, and can you ever address this with an unsedated stallion.
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Depends on the stallion I guess. I have two mules. One you can put you hand up inside his sheath and there is no reaction. The other will plant a foot on top your head before you can blink an eye if you even touch his sheath.