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You should try to at least wait until the puppy is 8 weeks, but the recommended time is 12. That's because puppies are really susceptible to hypoglycemia any younger than that. Puppies can still get hypoglycemic even after 12 weeks. At 6 weeks a puppy is not fully weaned from their mother and need a little extra time with their mommy. Also, when you get the puppy I would recommend you get nutri cal. This will help your puppy not to become hypoglycemic. Putting sugar in their water and food may also help keep their blood sugar where it needs to be. Make sure play sessions with your puppy are not too long because that will also help.