After a Jack foal is a yearling he has 3 things on his mind, sex, sex and more sex. They are not fully matured until they are 3 years old, like a Stallion or Rooster they will become very territorial. Just image having 500 pound Roosters wandering around.
To get them castrated (gelded) they have to be halter broke, able to be transported and it costs $400+. Sadly, it all adds up to being not cost effective. We have decided to sell off our 2 breeding Jack's and all the younger ones because I think I'm getting too old (79) to put with their foolishness.