Expert: Tina - 1/9/2009

Question
We have had our cat Frankie for about 3 years now and we
got another kitten in July of 2008. They were perfectly
fine this whole time. They would play, eat, nap and bathe
together - sometimes they would clean each other. Today,
Frankie started growling and hissing and Layla. Now, every
time Layla goes near Frankie, she will growl and hiss.
Sometimes they will actually touch noses for a moment or
just be somewhat near each other and be fine. For the most
part Frankie is aggressive. She is very affectionate with
us, though. Is there anything we can do to get them back to
normal? What is the issue and why did it happen so
suddenly? Layla doesn't know what's going on and actually
seems concerned. HELP!

Answer
First I am going to assume that both cats are spayed/neutered. If not, you must get that done ASAP as the new kitten may be producing hormones that are getting Frankie interested (even if he is neutered),

It is not very common for cats who normally get along to suddenly start to fight so aggressively, so a possible cause of this sudden fighting is redirected aggression - this occurs when one of your cats sees an intruder cat (or smells or senses him) and can't get at the intruder. She sometimes goes into fight mode and his body is flooded with adrenaline, and in that state she'll fight almost any other animal that she sees as a threat, or even gets too close. Redirected aggression can be helped by 1. keeping cats indoors 2. excluding roaming cats from your yard with fences (and cat-proof fence toppers such as chicken wire extensions) 3. Using Feliway plug-in diffusers and/or spray. Feliway mimics facial pheremones cats use to mark their territory by running their cheeks on things, and it is a big help with territorial aggression. You can find Feliway at most pet stores or online. I find the spray most effective but best of all is to use the diffuser for a constant level (it also seems to take 2 weeks or so to work) and the spray re-applied every 3 days. Spray it on doorways and furniture at cat-rubbing level.

Don't allow things to escalate, if they seem upset with eachtother, separate them for a few days and gradually re-introduce them as if they were strangers. Here is an article with info on how to do this to minimize the likelihood of aggression:

http://catnet.stanford.edu/articles/introducing_cats.html

Good luck!