aggressive younger femalel cat

Question
Hi Ali:) I have 3 cats at the moment. The first is a kitten I adopted from our vet 6 months ago. She is spayed & has never had a heat. The 2nd is a male Tabby who was abandoned and we found. He is neutered and declawed and about 1-2 years old. The 3rd is my problem and the newcomer. She is a young female who was given to us by a concerned neighbor who found her on their porch & couldn't keep. She is very aggressive with my other 2 cats, chasing and hissing, even though we have had her with the other 2 for almost a month now. She is scheduled to be spayed this coming Friday, and just had a heat last week, since then she has really been picking on my little girl cat, seeking her out and chasing her out of the house and I'm wondering if the spaying will stop the aggressive behavior. All 3 share 2 litterboxes, food, and the house without any problems other than the random chasing and hissing. All 3 are very affectionate with my husband and I, and up until the heat were getting on relatively okay. Thanks.

Answer
Rachel,

One issue that I can see right off the bat is that you need more litter boxes...Litter box rule of thumb is one box per cat plus one, in your case that makes four litter boxes. I would also suggest having more than one place where food and water is available. The aggression you describe could be territorial which is why I am suggesting some of the changes that I have. If the aggression gets out of hand isolate your newest cat again for 1-2 weeks and see if that makes a difference, just be careful not to ignore her during this time period. Since your new cat is going to be spayed shortly you may see a decrease in aggressive behavior, just with the hormones out of the way. When you have her spayed wait 2-3 weeks for the estrogen to leave her bloodstream, then reassess her behavior. If you have any further questions or concerns, please do not hesitate to contact me again.