According to Monhacky Animal Hospitals of Vista, new puppies often develop stress-related issues due to change in their environment, which in turn can cause a lack of appetite for food and drink. Other potential causes for a puppy's not eating or drinking include mouth sores, foreign objects in the mouth and canine distemper.
According to the ASPCA, a lack of thirst in puppies can indicate mouth sores, or a foreign object such as a burr or stick may be lodged in the mouth. Lack of water can lead to dehydration, which in turn can lead to a loss of appetite. Additional signs of dehydration include sunken eyes, depression and lethargy. Dehydration can occur during hot weather and can also point to an underlying illness. Puppies typically need to consume one ounce of water for each pound of body weight per day. It is important for new puppy owners to carefully monitor their puppy's water intake and consult a veterinarian if the animal is not drinking enough.
The Blackburn Animal Hospital explains that puppies are at high risk for canine distemper, an extremely contagious viral infection which can cause loss of appetite. Other symptoms include fever, depression, and diarrhea. It is important to vaccinate new puppies for canine distemper, as the condition can lead to paralysis and brain damage.