cat pooping outside of litter box

Question
I have 2 cats one is nasty to the other. The meek one will occasionally poop outside a clean litter box. I try to keep the dominate one from being nasty but it can hard. They are sister been together since birth. The dominate one seems to get more nasty as she ages. they are both 15. They use to be so close slept together and were never apart. Any help with both or one  issue would be appreciated.

Answer
Pris,

At age 15, they are both quite geriatric, and, just like people, older cats can become curmudgeons!  I suspect the dominate cat is doing just that.

However, I would have a vet check done any way, since as she ages, just like people, nagging medical conditions can occur, and these can cause a cat to become more cantankerous.

In addition, I would try a second litter pan in the same general area, just in case your dominate kitty is keeping her sister out of the communal litter pan. Again, it does not hurt to check them both for any parasites or impacted anal glands which may also result in pooping outside of the box. Another thing you might try is to put a plastic tray under the box lined with newspapers, so if you have a miss, it is easy clean up.

Please let me know how it goes.

Best regards... Norm.