Our 3 year old pit bull mix recently passed away. We waited a few weeks and noticed our 5 year old was missing her friend.
We adopted a 3 year old female lab mix and initially all was well. Now 2 weeks into our new family the 5 year old has become aggressive twice towards the 3 year old, and is withdrawing from me.
I make it a point to spend equal time with them, and none of our 5 year old dog's routines have been changed. What Can I do to make this easier on them?
Possibly the younger one now feels safe enough in her new home to establish her own rules and will now reach for a new position in the pack.
When the older one is scolded for/stopped while trying to supress that, she will withdraw - and will have more difficulties to keep her position as the original home owner.
To bring two adult females together is not creating the same scenario as when a puppy is introduced to an older dog, that might sort of 'adopt' it and teach it 'manners' for months which the young one will then remember for a long time, even if it is getting stronger and more selfassured over time.
'Equal treatment' is something that is valued by humans, not by dogs. Especially with female-female or male-male partnering there will be dominance issues over any kind of ressource (food, toys, your attention in any given moment, places to rest, places to watch from, whatever). You might be able to supress any kind of aggression while you are in the room, but only then.
At home partnering of female-male offer a better chance for developement of a friendly cooperation - drawback: outside there usually are other issues: most males will get reactive, showing other males, that they don't want anybody to come into contact with their female, so that this combination is not the one I would prefer for a walk/free play together in the dog park.
Look for expert advise (APDT-Trainer for example) for how to handle the situation in detail or even start to think of rehoming the new one. Best wishes and Good luck!
"Withdrawn" is a conclusion without supporting evidence. "Aggressive" is also a term that isn't sufficiently detailed in your post to allow for clinical interpretation.
In general, when you introduce a new dog into the household, you are upsetting the status quo. You can make the transition easier and safer by keeping the dogs separated when unsupervised, and avoiding situations where resources like food, water, toys, or attention can be competed for.
Joint activities like long walks together outside the house can often help dogs to form bonds in neutral territory. So can trips to the dog park, or time together at doggy daycare. I highly recommend all of these things, although they won't necessarily solve all your problems.
If you are unable to distinguish between social jockeying and serious threat displays, especially with bully breeds, then you need to engage the services of a trained behavioral consultant to ensure that both dogs have sufficient social skills and bite inhibition to (eventually) come to a working arrangement. Most dogs will eventually sort themselves out, but it is always the owner's responsibility to ensure they do so with minimal risk, and to redirect and separate the dogs if distance-increasing social signals aren't being respected by either dog.
