Welcome to our weekly 'Ask a Vet from the SF SPCA' feature on 7x7.com. Dr.Jeannine Berger, DVM, DACVB is a board certified veterinary behaviorist who counsels guardians whose pets’ issues are beyond the scope of training. Think of her as a pet shrink…at your service. Ask your own questions in the comments!

Q: How many cats is too many? I have two cats and moving in with my boyfriend who has one and his sister wants to give us her cat as well. Is there a tipping point?

A: Four cats can certainly live nicely together. The number of cats isn’t the determining factor in their quality of life. Rather, the nature of their relationship will be. The tone for the rest of their days together will be set by the introduction, so take your time and do it right. Adding cats that don’t know each other can be a real challenge and certainly can make some cats very unhappy. Female cats especially can become very aggressive when defending their territory, but most cats are actually fearful when they meet a new cat – in this case, a slow introduction can certainly help.

Success doesn't only depend on the cat’s personalities, ages and genders; but it also depends on the space you have available for the cats.  I recommend separating your cats into their own territories at first, giving the resident cat her favorite place in the house and confining the new cats to their own rooms with their separate food and litter boxes. Give them enough time to get used to each other and meet under the door crack, for example.

You can then start to do introduce smell exchange by switching cat beds or brushing all the cats with the same brush. If that goes well, periodically switch the rooms that the cats are in so that they may smell the other cat without the potential for a fight to occur. Watch for any signs of aggression or anxiety.

It is important to prevent them from interacting negatively with each other.  A bully cat will get more assertive and a fearful cat gets more fearful if they get into fights on a regular basis – and that will be hard to remedy.

You want to assure that all of the interactions between your cats are positive. Gradually reintroduce the cats to each other during controlled sessions.  Begin by having the cats at a safe and comfortable distance from each other in the same room, where neither cat shows signs of anxiety or aggression.

Also I recommend you use Feliway plug-in in the rooms where the cats are hanging out, to keep them super relaxed. Good luck!