Expert: christine - 8/21/2008

Question
My female border collie is 3 years old. We have 2 other dogs - both males. One is similar in size to her and the other is a terrier chihuahua mix (about 13 lbs). She has NEVER been an "aggresive" dog. No growling, biting, nipping or anything like that. In the last three weeks, I have caught her TWICE with the smaller dog in an aggresive stance, standing over him and "going for the kill" as it were. I have NO idea what has brought on this behavior or how to deal with it. She has never killed any small animals or bitten anyone. What has happened to my sweet dog and what can I do about it?

Answer
Well I have a border collie also. A two year old female and a month after i got her we took her to the park and she started attacking a little puppy. I think the main reason causing your dogs aggression is that she is in heat meaning she may want to get pregnant or she feels the need to be mean and show the little one shes the boss. Or i`Ive seen my dog do this with the bull dog under US. Barking at the neighbors chihuahua next door . the pit bull below us started barking at the chihuahua so my dog joined in. Maybe your dog is coping some others person`S  dogs aggression. well let me know how it goes but i suggest to keep them a part till this thing blows over or you figure something out!
good luck ;)