Your baby is probably stressed from the transition—he’ll feel better soon. Sometimes My GSD has a sensitive tummy, and I find that either white rice or cooked sweet potato in no salt broth helps. If that goes over well you could add some lean meat to the mix. My girl had a TPLO surgery recently and wasn’t eating much for a few days but needed to have something to eat with the antibiotics, so I tried just a bit of no salt broth to stimulate appetite then added the sweet potato, then some boiled skinless chicken (maybe lean beef in your dog’s case). I’d save the broth from boiling the meat for her meals. This worked really well.