Aggressive Dogs

Question
My dog's name is Snickers, she is a female Australian Shepard and I have had her for about 6 years, since she was a puppy. (making her 6 last month) We also has a 6 year old female Jack Russell named Casey, who we've had since a puppy as well.

These two dogs have grow up their whole life together.
When the two dogs come into season, Snickers gets rather aggressive and snarls a lot. In the last 5 years they have only fought about 3 times, and only when they are in season.
For some reason, over the last two months Snickers has gotten increasing aggressive and will often snarl at Casey, which will cause casey to attack her. They have gotten in MANY huge fights over the two months.
Recently, I left for college, while my mother and brother left for about 2 months for work related reasons. This left only my younger sister and moms boyfriend in the household. My sister doesn't care about the dogs and my moms boyfriend only cared about the jack, which led us to believe it was a jealousy problem. my mom and brother recently returned, but the fighting didn't stop. My mom even had Snickers fixed, thinking it could be hormones. She was just fixed last week, but today the dogs got into another large fight. my mom locked Snickers in the basement to keep her away from casey. Snickers then went downstairs and proceded to attack one of the household cats. my mom always says she has been following the other cat around for weeks, which leads her to beleive Snickers is going to attack that cat too given the chance.
There isn't much we could do to try and stop this behaviour other then seperate the dogs, which is even hard now because of the cats in the house (who eat in the basement where Snickers is locked up)

We are in the process of finding Snickers a new home where there are no other animals.

What could be causing this aggression in Snickers and why does Casey always react my attacking her?

Answer
Dear Ruth,
Thanks for the questions. There are many many possible reasons that Snickers is behaving aggressively. Dog-dog aggression is a complex issue and there have been volumes of books, articles and research about the subject.

They could be fighting over attention, territory, items or other resources. They could be fighting for social status. They could be fighting due to medical issues.

Stress in their environment due to changes in house members, schedules, et cetera can contribute to aggression.

A lack of structure, lack or exercise, poor nutrition, or human failures to provide dogs with their basic social, emotional, and physical needs are some other causes.  

Some dogs get a 'taste' of the adrenaline that is released in their brains during aggressive events and want to feel that rush again. It's like sky divers. Hmm... that was a great rush, I'll do that again!

I'm not sure why your girls are fighting. One of the first steps is to identify which particular instances, situations, activities, et cetera are likely to trigger the aggression.

You must identify the triggers before you can teach them to relax in the presence of those triggers. For more details, please visit my web site and read the page titled "Problem Behavior Solutions".

Casey reacts because she is being threatened.

I think your choice to place one of the dogs into another home is wise.

If you want to learn the best way to keep peace, buy the book, Feeling Outnumbered? How to Manage and Enjoy Your Multi-Dog Household. (Paperback)
by Karen B. London, Patricia B. McConnell

If you want to actually begin a behavior modification program, please contact a local trainer who is experienced with dog-dog aggression. Visit http://www.apdt.com to find a trainer near you.

Happy Training!
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