It sounds like, for one reason or another, he has an aversion to the litter box for defecating. It doesn’t really sound like urination is a problem, but may become one. You already have things covered well with having 1 litterbox per cat, plus one extra one. Here are some more tips:
Make sure litterboxes are scooped daily
Clean the entire litterbox every week (dump out litter, wash with soapy water, rinse, refill)
No litterboxes near food/water bowls
No litterboxes near noisy areas or appliances (i.e. private)
Litterboxes must be spread out in the house so they can get to one without being bothered on the way (by children, people, other cats)
With cats that don’t defecate in the box, I worry that there may be a problem with arthritis or pain when having to squat to defecate. It takes longer than urination and may be difficult for them, thus just doing it “anywhere” that it comes out rather than get in the box and “try” to go. Another problem could be that the cat is being bothered while trying to go by another cat, or is otherwise stressed. Some cats do not like the height of some of the litterboxes that they have to step into. Finally some cats are more picky about where they defecate than urinate.
My two cats share two litterboxes (yes, I need one more). One is filled with clumping litter. The other is filled with Feline Pine. My white cat urinates in the feline pine, but only defecates in the clumping litter so he can bury it better. My other cat does both in the clumping litter.
At this point, I would have a kitty litter “buffet” with different litters in a private spot (clumping, clay, sand, Feline Pine, shredded paper, cloth rags). Also give choices such as high lipped catbox, covered catbox, “low lip” catbox such as a top to a cardboard box, etc. Also consider videotaping your cat to see what he does before defecating – gross, but can help understand his problem. You may want to conduct the experiment by shutting him up in a room where the other cats cannot bother him.
I hope this helps answer your questions. Please let me know if you have any more questions or concerns.
Feedback is greatly appreciated.
Sincerely,
Dr. Amanda
Dr. Amanda
Small Animal Veterinarian
Special interest in canine and feline behavior.