I get asked on occasion and from shocked pet parents about their adult dog attacking their new puppy. Comments like "they love their dog friends" and "they have never acted aggressively before".
My first question is how old is this new puppy? If they are under 6 months old then your dog is probably displaying puppy aggression. This is a common behavior we see with adult dogs who encounter very young puppies.
Exactly why your dog doesn't like puppies might be a few reasons.
They have not met or interacted with puppies prior and are scared.
(Most common reason) They have interacted with puppy's and just don't have the patience for this puppy's rude and bazar body language.
The dog is not given another means to escape from the puppy and eventually gets fed up.
Pray drive. The desire to hunt and attack small animals that look like pray. Small dogs or puppies can easily be subjected to this predatory behavior.
In order to keep every one in the home safe and to ensure your puppy doesn't have a traumatic experience upon arriving into their new home. You should set up a puppy room or space.
Your puppy will spend their first weeks and sometimes longer in this area always separated from the other dog. Both dogs can see, smell, and hear the other one but there are no negative emotions because they can safely dwell in their own private spaces.
As I mentioned puppies can be extremely rude by nature to a mature adult. Their lack of personal space is no exception. A young puppy is not going to understand boundaries and will quickly over step the other dogs limitations if allowed to constantly interact. It is the Pet Parents job to ensure that the puppy respects the adult dog don't just "let them figure it out".
When it comes to picking where to set up your puppy area -- I like the kitchen or dining area because they are spaces you are probably in a good portion of the day. This space will offer a wonderful opportunity for training and bonding with your puppy while your dogs are getting acclimated to each other.
You cannot expect your dog to be okay with this new family member right away. Their life will be impacted by you getting another dog and they will no longer get all of the food, bones, toys, affection, and time with you ALONE! They have to share now.
To ensure that this change goes soothly you want to start establishing consistent routines that both dogs can come to rely on. Feeding at around the same time every day, in the same location or way. Routines for walks that are calm so that your eventually 2 rambunctious dogs don't knock you over in their excitement and race to get out of the door.
Determine what will your sleeping arrangement be. It's totally okay to allow one dog on the bed and keep one on the floor but you need to make sure that you train them each what is expected of them.
Where are their day sleeping areas? Be sure that each dog is given their own designated beds and dens. Waiting until the puppy is old enough that you can teach them to leave the resident dog alone when they are in their bed/den is really important. Another reason for waiting to put them together full time.
The end goal is to help the dogs meet slowly, get used to the new changes, and then to ensure that the dogs respect each other's space and needs.
I will say it one more time this is not a process you should rush. Take as long as you need to and it will be quicker than rushing.
If you need help with introducing your new dogs KAS can come up with a plan with you to make the process smooth. If you have already ended up with some aggressive or worrisome behavior when trying to introduce your new dog to your resident dog do not wait to get help!