Sadly, I have experience with this. It is called Bitch Aggression. For us, our older female became aggressive towards a younger female when the younger one became sexually mature. They had been friends up until that point. The older female started "guarding" the resources (our little male), and gradually the attacks became more frequent and more violent so that the dogs had to be kept apart.
I re-homed the younger dog, and thought the problem was solved. However, as soon as another female puppy that we had became mature, the older female started attacking her also.
After several consultations with trainers and our vet, I rehomed our older female. She is now in a home that has no other pets, and is doing quite well.
I've been told that once this behavior starts it is almost impossible to ever trust the two females together again. I wish you much luck with your puppies.
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LaVail Yorkshire Terriers |