Cat pooping outside the box

Question
I have a 13 year old male cat along with 2 other cats. (one female and one male). My 13 year old has recently started pooping outside his litter box. 3 weeks ago I purchased a covered litter box because he has never covered anything up. He has been using the box until 3 days ago he started pooping outside the box. I do have another litter box that the other 2 cats use. All the boxes are cleaned on a daily basis.  What can I do to correct this behavior?  Or is is just old age?

Answer
Hi there!  It doesn't sound as though your cat may be stressed.  Any type of change (ie. the litterbox) can cause a cat to behave in abnormal ways.  One of the most common way is by urinating or defecating outside the litterbox.  I would definitely think that this litterbox has been a part of his life too long for him to suddenly, after three weeks time, stop to use it.
Older cats develop something called Mega Colon.  This is where the colon muscles literally begin to not work properly.  This causes some constipation and painful defecation.  Because of the pain during defecation, the litterbox is then associated with the pain, leading to the cat no longer wanting to use the litterbox.
Mega Colon is treated with two medications.  Cefulac Syrup and Cysapride.  Both can go right over the food.  Laxatone or CatLax work as a laxative and are often times part of the treatment.
I would have your veterinarian take a look at him to decifer whether or not this is the problem or if the problem is do to a delay in a stress issue because of the new litterbox.
I hope this helps!
Hilary