Q: I just adopted a new kitten and already had five cats. Now one of my cats is using the bathroom outside the litter box and I can’t figure out which one. What do I do?
A: Inappropriate elimination is a common problem in multiple cat households, and it sounds like you have upset the delicate balance in your cat colony by adding just one too many felines.
Cats will eliminate outside the litter box for several reasons, such as illness, inadequate training, undesirable substrate (most cats prefer a soft, sandy grit), too much traffic in the area, marking behavior (some cats simply will not go where another cat has), and sometimes they will do it simply to show you they are displeased.
First, I would suggest that you get one litter box for every two cats in your house. Since you have six cats now, three litter boxes should be a good number to have in various locations around the house.
Second, and I cannot stress this enough, make sure you keep the litter boxes cleaned of solid waste daily, and change the litter completely in all three at least once a week, more if necessary.
Also, make sure you thoroughly clean any areas where accidents occurred, remove any area rugs, clothing, or anything they may have eliminated on. The new kitten should be familiar with the location of all three, but more importantly, keep it confined to a small room until it is eliminating in its own, personal litter box one hundred percent of the time. Then, you can let it out into the rest of the house.
If you allow the kitten free roam too soon and it starts peeing and pooping in corners and other inappropriate places, your other cats will come along and “cover” up the scent with their own. This can turn into a stinky, expensive nightmare.
If it is an option for you, you might try making a few of them stay outside for several days. If not, you can confine your cats in small rooms with a ratio of two cats per litter box, until they understand exactly what is expected of them.
Finally, you might need to board your cats for a couple of days. By being kenneled, the cats will have no other alternative but to eliminate in a litter box, and it might just be what they need to get them back in the right habit.