Is it safe to give a puppy liquid whey left over from cheese making? I read somewhere that it is fine and I am curious if that's true as it sounds a bit crazy for that to be true to me.
According to Wikipedia, whey contains 6% lactose we know from the answers to the question Is it OK to feed dogs dairy products? that giving dairy products to adult dogs is problematic. We also know from the question If my pet is lactose intolerant does that mean they can't have any dairy products? that lactose can lead to flatulence, diarrhea, nausea.
Many commercial dog food products include protein from whey, but that is a processed product (presumably with the lactose removed).
A puppy who should not have developed lactose intolerance, and should be able to digest MODERATE amounts of whey just like they would a complete milk product (see related: Question about getting a mother's milk from another species)
Watch for loose stool and/or gas, don't over feed, discontinue before the puppy matures.