Why doesn't he like his food anymore?

Switching foods quickly can cause stomach upset. If you didn't switch slowly (replacing the old food with the new gradually), that might be a factor.

Generally, a dog won't refuse food for long unless there is a medical problem. Try not to give in by adding tempting people food. Just stick with the dog food (pick one, or mix the two) and your dog should decide to like it soon. If not, I recommend taking him to be checked by your vet.

My first thought is that you should have the pup checked out by the vet. We thought nothing of this behavior in our 7 year old dog, so we ignored it and changed her diet to more palatable things, and it turned out that she was sick. Now, I know that what she was sick with wouldn't have made a lick of a difference if we had caught it early vs late (it just so happened that she had terminal cancer, admittedly), but it feels a bit like I failed as an owner by not taking her to the vet in the first place when she lost her appetite. The vet has since told us that you should always take your dog in when they lose their appetite, and that it's far worth the risk that there's nothing wrong at all, and also considering that if the dog is sick, there's a far more likely chance that you can do something about it if you catch it early than you do if you catch it late. I hope that all made sense.

Look, I don't want you to think that I'm alleviating my guilt or something such by telling you to risk wasting money at the vet's. Like I said, it turned out with my dog, there was nothing they could do no matter when they caught her cancer. But that's not the reason I'm telling you to go see the doggy doc. The reason I'm suggesting you do so is because if there is actually something wrong with your dog, whether or not they can fix it, you'll feel really guilty as a dog owner knowing that you neglected her for so long if you never took her in until he/she got noticeably worse.

Lastly, let me try to restate that confusing mass of clauses at the end of the first paragraph. I was trying to say that the vet told us that you should always take your dog to the vet in the event that they stop eating, because the chances they are sick are high enough to warrant it, and also that the value of finding out you could treat or cure the illness they may have is worth running the risk that you'd be wasting your money by taking what you didn't know was actually a healthy dog in the end to the vet's office. Did that make any more sense?

Okay, I'm done now. I just think all of that is food for thought (no pun intended given the whole subject of this thread)

Puppies have varied appetites. Some days they eat more some less. As long as they eat something, you're okay.

Don't force your puppy to eat more. For many breeds especially large ones, its harmful. if you force your dog to eat more than he should it can cause rapid growth that their body and bones aren't ready for. Thats why dog foods will always say "this is recommended but vary according to your individual dog"

You may have just not seen this before and it seems like the new food triggered this. Honestly puppies just vary in the amount they eat. My terrier puppy sometimes only eats half a cup but if there is a visiting dog she'll eat two cups!

And I do agree if and when you switch dog foods take at least 10 days to switch them out. Otherwise it messes with their digestive system and they'll put themselves on a fast to avoid their stomach from hurting.

Namasté,

When dogs get older sometimes their teeth hurt or fall out an it gets hard for dogs to eat certain food types.

Namasté, Marcus