I don't think that's a good idea. Years ago it was a common practice but hindsight is 20/20. Castration is surgery. The only person qualified to do surgery is a vet. Even a simple surgery if not done properly could be fatal to your horse.
unless in your story you are talking about yourself in dialogue you should stick with I. for example if you were to say "That's Me." I said, grinning from ear to ear with excitement. then it would be...
You do it no matter how scared you are if you love the other enough and youself enough then you have the guts and heart to do it. then that means you are truly different dont be scared to take risks...