Is it OK to mix my dogs dry food with cottage cheese?

I have never heard of this. I would call your vet

I have never heard of a problem with cottage cheese. The only thing that may be a problem is gas! It might be a little smelly around your house! I'm just wondering why you would want to mix his food with it? It's best to stick to a well balanced, healthy dog food that has all the nutrients your dog needs to have, for his benefit.

Yes, stick to dog food. If under a year, any high calcium additions can harm its bone development.

I wouldn't do cottage cheese.. If the dog is losing interest in the dry food try a little wet dog food.. that's what we usually do