Continue to socialize him with the farm animals on a daily basis, bring him with you when you do any routine activity with your stock.
And then keep a close eye on him, correct him the moment he shows the urge to chase the farm animals. If you want, you can just put him on a (long) leash, so you can have more control over his undesired behavior.
You have to remain consistent and do this day in, day out, until he starts maturing and showing improvement. Constant supervision and reinforcement of appropriate behaviors in the beginning and whenever a new situation occurs (like lambing for instance) is essential.
As for something to chew on, I always recommend bully sticks, as a rawhide can be dangerous, but you can also give him raw bones or antlers (antlers last for a really long time). That will definitely keep him occupied.
Being that he's still a puppy, he has tons of energy, but I bet your older dog doesn't have the energy to keep up with him. So try to play with him every day for half an hour or so, if you can.
Like the Great Pyrenees, Tornjak's have a pretty soft temperament when compared to most other LGD breeds.
But a well bred, adult Tornjak should always protect its owner and its charges from a threat. So hopefully in a year or so from now, you will see a more protective side of Nanuq.
