Dear Dr. Thompson: Around September, we were feeding a black cat that sprayed the first time we came out to feed him. At the time I thought it was to assert dominance, but when the cold weather came and we brought him inside, he was sweet and docile as could be. He is still quarantined from our other cat, but the concept of a litter box is lost on him. He's not aggressive toward our house cat, but she has hissed at him. How should I integrate him with our house cat?
ANSWER: There are a few vital steps that you need to follow before introducing this cat to anyone in your household. Isolating him from your other cat was a smart move because there are any number of potentially serious problems he could be harboring from his time outside. Frequently, outdoor cats carry a number of intestinal parasites, and some of these can even be contagious to people.
He may be carrying viral diseases that could be fatal to your other cat. Fleas and other skin parasites could be brought into the house. Many of these conditions are not readily apparent and some simple tests and an exam by your veterinarian will help identify many of these issues. Fortunately, many are straightforward to treat. When he has a clean bill of health you can start integrating him into your house.
Using a litter box is instinctive to cats, and simply placing him in the box and following some simple rules with multiple cats will avoid many litter-box problems. Have one on each level of the house and one more box than you have cats, which in your case would be three boxes. Scoop them often and clean monthly with soap and water. Avoid fragranced litters and keep the boxes away from heavily trafficked or noisy areas. Make sure they are large enough for the cat to stand and turn around.
Introducing the two cats may be more involved. This should be gradual and supervised or someone may get hurt, including you. Remember, he is on alert and used to defending himself, while your other cat has had her world turned upside down with his arrival. They have had a chance to get used to the presence of one another during the quarantine; now start with someone holding each cat a distance to acclimate them to the sight of a new cat. There will be some hissing and spitting, but keep a safe distance and maintain control.
Over time it will become less traumatic and eventually they can be allowed some supervised time in the same room. Behavioral and physical problems can develop if conflict exists, and taking steps to ease them into cohabitation will help avoid trouble down the road.