Ridgetop
Herd Master
If a young dog is keeping your goats penned in an area near their normal night pen, it could be that the dog is worried about predators in the larger field. He can smell and hear predators which you cannot and if he judges he is outgunned by the predators will not want to try driving them off.
A young dog (yours is only 5-6 months old and a puppy) that realizes he is not able to protect his goats against a larger threat will be much more cautious about allowing th herd to spread out to forage. The larger predator threat may be anything from a couple of large dogs to a cougar, bear, several coyotes, etc. The young dog will try to keep the herd in a small group that he feels capable of protecting. In the larger field he will have to guard on many sides over a larger territory. If he keeps the herd grouped tightly in a small area (particularly if he can back them up against a safety barrier with which he is familiar - in this case the gate and fence to the night pen) he has a smaller area to guard to keep them safe. It is possible that the larger field is too much territory for him to protect at this age. He is willing but knows he is at a disadvantage and so he is keeping the herd tightly corralled is a space he feels he can protect.
Can you divide the larger field into smaller pens maybe with electro net or some temporary fencing?
A young dog (yours is only 5-6 months old and a puppy) that realizes he is not able to protect his goats against a larger threat will be much more cautious about allowing th herd to spread out to forage. The larger predator threat may be anything from a couple of large dogs to a cougar, bear, several coyotes, etc. The young dog will try to keep the herd in a small group that he feels capable of protecting. In the larger field he will have to guard on many sides over a larger territory. If he keeps the herd grouped tightly in a small area (particularly if he can back them up against a safety barrier with which he is familiar - in this case the gate and fence to the night pen) he has a smaller area to guard to keep them safe. It is possible that the larger field is too much territory for him to protect at this age. He is willing but knows he is at a disadvantage and so he is keeping the herd tightly corralled is a space he feels he can protect.
Can you divide the larger field into smaller pens maybe with electro net or some temporary fencing?