How to Introduce a New Kitten to Your Cat
So you decide your cat is lonely when you are gone all day. You think that you should get another cat so he will have company. Most people believe that cats just automatically get along. But cats are typically very territorial and will his and act in a negative way as soon as you bring that new kitten home.
Many times this invasion will cause fighting, going to the bathroom outside the litter box, the older cat bullying the younger cat and spraying if it is a male cat. This causes causes a lot of tension not only for the cats but the entire household.
The key is the proper introduction of the new kitty into the household.
Do not rush the introductions it will cause resentment on the cat that was there first. Cats are very in tune to changes in the household. Even a loss of a person in the household can bring on an emotional reaction from your cat.
Bring the new kitten in very gently, take your time and keep them separate from each other completely at first, sometime for up to 3 weeks. Give the new kitten a lot of attention but do not let the other cat see you give that attention and always have the door closed. Then each day let them spend a few minutes together 3 or 4 times a day, making sure you supervise this interaction. Gradually increase the time they spend together each day.
If there is hissing or fighting or if it escalates into a chasing and attacking scenario, separate the cats and try again the next day. If the behavior is extreme separate the cats for a couple of days, then try again.
When you start to observe positive interactions between the two cats then you can gradually increase the time they spend together.
Since the cats have been separated for a while and have separate litter boxes already I would continue this for quite a while, maybe even up to 6 months. In some cases you may need to keep two litter boxes forever. For some reason the litter box seems to be a very territorial issue.
Be sure to have one on one time with both cats each day. Sometimes the cite kitten gets all the attention and the older cat is left out, this will just reinforce the resentment and may make the older cat return to his bullying ways.