Congratulations on your new puppy, and thanks for saving a life. In order to ensure you don't put your existing household pets in danger, it's important to have a quarantine period as well as a time for adjustment so your other dogs are not contaminated by a latent disease.
Your Pound Puppy's Life Thus Far
The thing about pound puppies is that shelter workers don't always know how and with whom the puppy lived before arriving at the pound. Sometimes, when a person is surrendering a puppy they have had a while, the shelter gets some history on the dog. More often than not, however, stray puppies are brought in after being picked up off the street and nothing is known about them. The shelter (it's no longer considered PC to call it a pound) then has to run tests on the puppy to make sure there are no communicable diseases before allowing the pup to engage with the general population.
There are some communicable diseases the puppy can acquire via his mother's milk. Many of these diseases, while in the incubation stage, cannot be detected by normal blood or fecal testing, while others require further testing. For example, the parasite that causes giardia sheds its eggs intermittently, so a minimum of three fecal samples taken over a week's time is the best way to detect it. Therefore, the first thing you need to know when determining how long to keep your puppy way from your other dogs is how long the puppy has been at the shelter. If the puppy has been there longer than 10 or 12 days, your quarantine time will be shorter than it would be if the puppy has been there only a few days. Even if tests show the puppy is healthy, it's possible the puppy's body is cooking up something very unhealthy. If the puppy was in the general population when offered for adoption, you can be reasonably sure he's healthy.
One- or Two-Day Minimum
Depending on the puppy's overall health as determined by the shelter vet, you should keep your puppy away from other household dogs for a minimum of 24 to 48 hours, longer if the puppy shows any signs of illness at all. This will allow the puppy time to settle in before enduring the stress of meeting new dogs who are undoubtedly older and have their pack established. The stress of meeting new dogs can cause your puppy to have diarrhea, as can changing his food. It's important to know if this problem is caused by stress, changes in diet or something more sinister, such as an internal parasite. Assuming your dogs are all vaccinated and healthy, this 24- to 48-hour time should suffice.
Longer If Necessary
If you have fears regarding your dogs' reactions to the new puppy and are more concerned about that than potential medical problems, take it one day at a time. On the first day, allow the puppy complete privacy. If the puppy appears healthy after 24 hours, introduce him to the household dogs under strict supervision. If the household dogs seem accepting of the pup, give them time to work out their status in the pack. This may be a little dicey since the pack is well established. If the puppy seems frightened or if your dogs show signs of aggression, stop the meeting and try again the next day. If all goes well, put your puppy in a room with a baby gate at the door so the puppy and dogs can get to know one another safely. Once you are sure everyone will get along, remove the gate. This can take anywhere from an hour to a week, so be patient and, for safety's sake, don't rush it.
Michelle A. Rivera is the author of many books and articles. She attended the University of Missouri Animal Cruelty School and is certified with the Florida Animal Control Association. She is the executive director of her own nonprofit, Animals 101, Inc. Rivera is an animal-assisted therapist, humane educator, former shelter manager, rescue volunteer coordinator, dog trainer and veterinary technician.