Out of the blue, female cat is showing aggression toward male cat

Question
Good Afternoon,

I have two cats (male and female) who have lived together for four years. They are both spayed/neutered and have always been very good with each other - cuddling, eating together, using the same litter, etc. Five days ago, I added a second litter box and changed from clay to pine. At this time, I also switched to a higher-quality, natural cat food.

Since then, my female cat (who is 4.5) has been extremely aggressive toward my male cat (who is 5.5). They got into a serious fight the first night while I was sleeping. I separated them and have mostly kept them in separate rooms since the fight (which causes almost constant meowing while I am in the house). I have also switched the litter back to the clay type I've always used and have been feeding the aggressive cat a natural calming liquid (with valerian root and a few other natural calming agents).

I've tried to reacquaint them on several occasions and my female cat continues to hiss and growl, even now on the 5th day. When this happens, I stand silently between the two cats until one or the other loses interest, and if that doesn't work, I throw a toy to distract them and they move away.

The situation is becoming very stressful for me, and I imagine them as well, as I've been losing sleep and now have to spend a significant amount of time coaxing them in and out of rooms and keeping them calm.

Is this normal cat behavior when a change like that is made? Could there be something else wrong with my female cat to cause this aggression? Is there something else I can do to help them reacquaint with each other? Any insight you can provide would be greatly appreciated.

Thank you for your help!

Danielle

Answer
Hi Danielle,

Sometimes moving stuff around will stress a cat out. And it might be what is causing the problem. I think the change might have been a bit too much, too fast. The food change and the litter change are two major parts of a cats life. Changing the litter back was a good idea. The food also may be a problem. Your female is pissed about the changes. And your male is who she is blaming. Second litter box is good. But I would have left the other exactly the same as it was. Also the type of box may be upsetting her too. I suggest owners get this box. I have never heard of a cat being mad about this box. Almost all of them love it.
http://www.google.com/products/catalog?q=petmate+giant+litter+pan&rls=com.micros
Try some Feliway Comfort Zone. That will also help. And just in case, look around and see if something else set her off. Does she look outside the window? She may have seen another cat outside and this set her off. Make sure there isn't anything like that. If there is make sure she can't see it again. Try a cat intro protocol. This will help. And keep up with the calming liquid. Give it a bit more time. In a bout 2 weeks all should be back to normal. Good luck and take care.

Ciao, Karen