Isn't it possible to have several hundred acres of your own land and place 20 sows and 5 boars on it in hopes of letting them free range there until you gather them up for slaughter?
No way. 25 hogs would be off of several hundred acres the first night. Fence won't keep them there, they will root under it. You turn 25 loose you will not gather all of them back up as you say.
Likely it is illegal to do unless you have permits from the state. You aren't going to get it for hogs.