Some breeds are known for more problems with dog to dog aggression, but in general, it is the management and sex and hierarchy that may make enemies of some dogs in the same household.
When that escalates to real fights, it is not fair to make them have to live the rest of their lives with a sworn enemy around and on their toes about it, better to rehome one to a suitable new home.
Some of our dog club members have that problem and, being good competition dogs, they just kennel them and manage them separately.
A friend has two right now, a border collie and a rat terrier, that she keeps in separate kennels.
I don’t know, I don’t think I would do that to both dogs, just because they serve a purpose of my own, but maybe I would try, if it happened to my dogs.
We have been lucky that we never had dog fights with any dog of any breed and at times we had up to 7 dogs in the house, from a saint bernard, aussie, rottie, dobies, minpin and always toy poodles.
We always had a grumpy toy poodle that ruled the roost with an iron paw.:eek:
Guess we were just lucky there.
I don’t think anyone can say what breed or sex would get along with certainty, as problems may crop up with any breed or sex combination.
Of course a sheltie won’t get into the kind of fight a pit bull would.
Even if a sheltie didn’t like another dog, they are some of the less aggressive dogs around.
There are studies that show clearly that raising two puppies together, if of the same litter or not, tends to be one situation where they may, once they mature, if both are about the same dominance level, start serious fighting.
That is the only situation we can say definitely that, unless you are going to raise them at least part of the day, every day, clearly separated from each other, if you let them raise each other, your chances of them fighting it out as grown dogs is much higher than if they had been raised in different households.
It is very heartbreaking to have pets living together and one day some start to fight so seriously they injure or even kill, but that is dogs for you sometimes.