Hi,
Congratulations on your new puppy. It is always hard for a young puppy to go through a transition, particularly shipping to a new home. I would be concerned if he goes more than a day without eating anything as these guys don't regulate their blood sugar very well at a young age.
Get some Karo syrup (don't use honey) from the grocery store. Maple syrup will work as well. Put some in an eye dropper and give him about a teaspoon. That should perk him up. Get some really good puppy food (moist) - add it to his kibble. You should be feeding the same stuff that the breeder was feeding for a few weeks.
If he is vomiting or has diarrhea, he needs to be seen by your vet ASAP.
Please let me know if that doesn't work, or if you need more information.
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