I have two mixed breeds dogs both from the pound. One is 6 and the other 7
years old, both spayed females.

For 5 years they have been together in the yard, in the house, sleeping in
the same room, yada yada.

Four days ago one of the dogs, a labrachow, started posturing with hair up,
tail out, frozen stance whenever the other got near her. Then without any
provocation that I can detect, she attaks the other dog and it is serioius,
not just some alpha dog putting another in her place in the pack. These
fights bring blood, and they have to be forcibly separated. This has
occurred at least five times even though we have tried to keep them
separated and it does not seem to be resolving itself.

Has anyone seen this behavior before and can anyone explain it or know how
to stop it? I am afraid we will have to put this healthy and family
friendly dog down because I would be scared to have her adopted by someone
else given her present aggression and we cannot keep these two physically
separated all the time as we work and also have 2 labradors on premises.

Thanks for any advise--Jim