Most puppies cannot tolerate cow's milk and will have diarrhea. This is because dog milk is low in lactose, high in protein, and high in fat, whereas cow's milk is high in lactose, low in protein, and low in fat. Most puppies cannot tolerate lactose, leading to diarrhea, and severe cases may cause inflammation in the gastrointestinal system. If possible, provide puppy food and clean water. Adult dog food has relatively low fat, which cannot meet the needs of puppies. If puppy food cannot be provided, you can feed egg yolk, chicken, lean meat, and an appropriate amount of rice. Dogs like duck liver, but do not feed it long term. Also, dogs should not eat too much salt; try to minimize salt intake. Remember to keep warm and avoid sudden temperature changes. A 40-day-old puppy should begin immunization protocols. If the origin is unknown or you cannot be sure of its health, first administer a high-immunity serum injection, and start the immunization program 10 days later.