Expert: Tina - 3/22/2007

Question
I have 2 female cats who are sisters.  They are about 3 years old and spayed.  I've had them since they were kittens and they have gotten along great (playing nicely, grooming each other, and napping together) they are mild mannered and very affectionate with my family and each other.  This all changed today.  When I arrived home this afternoon, I found feces and tufts of hair in the kitchen with one of the cats under the table hissing at the other who was across the room.  The hissing cat, Doodles, has been brutally attacking the other when they are in the same room.  We separated the cats and up them in separate rooms.  Doodles saw her reflection in the mirror and again began to hiss like crazy.  We tried to reintroduce the cats to each other several hours later and Doodles again attacked the other.  Is there something that could explain Doodles current behavior? Could she be ill, or has something disturbed her?

Answer
Hi Heather,

It is not very common for cats who normally get along to suddenly start to fight so aggressively, but there are 2 likely reasons that this may happen in my experience.

The most likely 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.

Nutritionally, you can help reduce aggression by supplementing your cat's food with tryptophan, an amino acid that is a serotonin precursor and helps mellow out mammals. You can buy it at some health food stores and online at places like vitaminshoppe.com. Get capsules, you can pull the capsules apart and sprinkle the powder on canned food and mix in - it has pretty much no taste so your cat should eat it fine. tryptophan is much cheaper and just as effective as "kitty prozac" sold by vets. Also it is very safe, since it's just an amino acid present in meat there is a very good safety margin. I recommend giving 500 mg a day per cat.

Since their encounter was so sudden and violent, I would separate the sisters 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

Another (less likely) explanation is that when a cat is ill, sometimes they smell different, and instead of smelling like a lifelong friend, she suddenly smells like a stranger to your other cat. If you suspect that either cat is not well, or if you simply want to rule out this possibility, take both cats to the vet for a thorough exam including blood panels. Also, sometimes a scary experience like a vet visit will actually make the aggressive cat forget all about their vendetta :)

Good luck!