I am running a plugin that prevents mobs from spawning, except for those that we designate are allowed using the Spigot Spawn Event Reasons listed here: https://hub.spigotmc.org/javadocs/spigot/org/bukkit/event/entity/CreatureSpawnEvent.SpawnReason.html. One issue I came across recently is that none of the farm animals, except for the sheep, have a spawn event tied to them. Even the sheep's spawn event is only tied to being sheared. This happens because we prevent any "DEFAULT" mobs from spawning, as any new mobs that get added with version updates have this event by default and we don't want hostile mobs in our territory. If you could implement some spawn event to these mobs based on their neutral/passive state that would be great.