mutation (a spell that can be acquired at winborn at the magic academy and have a vast kind of effect from add a trait,to change genetic or physic atribute of the slave) or potion (alchemy station)
Mutation might work but that's not reliable and can do like anything. There is no potion to stop lactation unless I am really missing something. I've searched through the list a few times. I enabled the lactation stops rule i assume it takes a bit to occur?
