feuding siblings for the first time!

Question
I have two cats which are siblings I received from the humane society when they were a few months old (1 female which is spayed, 1 male who is neutered). They are now over two years old and have always been best buddies... until monday night. The female started hissing and growling at the male, the male was crying. After repeatedly seperating them they were so focused on each other it was scary! I ended up keeping them in seperate rooms. The next day I saw blood in the female's litter box. At the vet office they drew urine, said it was bloody, gave me antibiotics, and also changed her diet due to presence of crystals in her urine. Well, two days later, I reintroduced them after not seeing each other for 24 hours and they are still figting! Have you ever heard about this before? Will they get over it eventually? What is the best way to hendle it? For now I've kept the female in the extra bedroom and the male in the office while gone, and only let the male out while I'm home. The female is still extremely sweet to me and I've been trying to split my time between them. Please help! Thank you in advance!

Answer
Christina,

It sounds like it may be "Redirected Aggression".

That happens when a cat sees a strange cat outside and  becomes territorial, but can't get to the strange cat to defend his territory. The cat then turns on the closest animal member of the family and fights with them as if they were the other cat. You may not see the animal that the cat sees.

The first thing you need to do is block the window past the cat's eye level of the window he can see another cat out of (out of sight, out of mind). If it is allowed to go on your cat may develop a permanent personality change. Also put the cat in a room by itself for at least 4 hours to calm down when she behaves like that.

There is a very popular cat calming spray and plug-in you can use called Feliway. It is available at pet stores or on-line. It copies relaxing pheromones that cats produce from rubbing their faces on things.

There is also a calming product that you can add to the cat's food or water that reduces anxiety called Bach's Rescue Remedy. It is available on-line, from the vet (they use it too), and in health food stores. Here is a link about it:
(copy and paste, or type the whole links into your address bar) http://www.bachflower.com/Pets.htm

If your cat is still being very stressed the vet can put her on "kitty Prozac" for a short term (usually 2 weeks) until she calms down. You may want to speak to the vet about it.

I am including links to 2 good articles on Redirected Aggression that may be helpful to you:

http://www.sniksnak.com/cathealth/aggression3.html

http://www.littlebigcat.com/index.php?action=library&act=show&item=redirectedagr...

Urinary crystals are very painful. She may be striking out in pain at the other cat instead of in anger.

Tabbi