Friends now Foes

Question
I have two cats, a brother and sister from the same litter. They are almost 2 years old and have gotten along great, they even groom eachother and snuggle when sleeping. Three months ago I transitioned them into indoor and outdoor cats, meaning they have a cat door with access to the house but no more litter box, yay:). My problem is in the last month the boy cat has begun hissing at his sister and chases after her. If I try to break it up he goes after me too. The girl cat doesn't seemed too phased by the hissing but he chases her out of every room she enters when he is in there, and since they like to be in the room I am in she is being left out. What can I do to make them go back to being friends?

Answer
Hi Amber,

First of all, I will assume both cats are spayed and neutered. if not, that's your first problem!

This is one of the many reasons that I do NOT recommend allowing cats outside. Cats allowed outside are subjected to danger from cars, wild animals, contagious diseases, poisoning from rat poison and other materials, nasty cat-hating neighbors, and the list goes on and on. Not having a litterbox is not worth the risk to your cats' health and lives. If the litterbox is a problem for you, try enclosing it ina  bench, for example some are sold at www.drsfostersmith.com or you can use an old toy chest, cut a cat-sized hole in the side and place the litterbox inside. Now the box is out of sight and litter scatter is contained.

In addition to these dangers, the urge to establish and defend a territory causes many cats to become aggressive to other cats - including those they have lived with in harmony before.

So, please consider keeping your cats strictly indoors, or you can consider building a cat enclosure. These things are great because they give the cat fresh air and the feeling of being outside without all the dangers!

More info on cat enclosures:

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

To help your cats get along again, try using the Feliway spray (sold at most pet stores) you apply it to doorways and furniture at cat-level in your home and it contains a pheremone that helps reduce territorial aggression in cats. It must be re-applied every 3-4 days. Feliway is also sold as a plug-in but the plug-ins are not as potent.

Good luck!