My neutered cat mounts his sister. How to stop their fighting?

Such behavior can be a dominance issue and in older pets may be a sign of changing social dynamics and i would schedule a vet check to rule out any medical causes. The comfort zone diffusers for multicat household or the original feliway pheromone diffuser may help but i would not introduce a new kitten until things settle down

They may always be enemies but there are a few things you can try to help calm them. I would start by putting some feliway diffusers throughout the house. They have a multicat version now. Feliway is a feline pheromone which is helpful to calm cats. It doesn't work on all. You could also consider putting some essential oils throughout the house. Be sure to get ones that are safe for cats. Visit oilyvet.com for more information. Also, make sure you have at least 3 litterboxes throughout the house, if possible, to prevent competition. If all this fails, you could talk to your vet about putting one (the instigator) or both on an antianxiety medicine to help calm them. I hope this helps!

If the new cat isn’t neutered that needs to be done right away. If he’s neutered then I would use a pheromone diffuser like Feliway, and consider giving a calming supplement like Solliquin. If needed clap you hands and say No, or distract him with a treat, toy or laser pointer so he has another acceptable thing to do. Usually once the dominance issue is resolved this behavior will stop. Thanks for using Petco Pet Education Center, formerly Petcoach to help you care for Zeplin.

It does usually take a few months for all the hormones to dissipate post neutering, however if the cat was neutered at a much older age, he may still have some of the behaviors/interest even without the ability. Keeping the cats separated if this behavior occurs, or even adding in a pheromone diffuser (such as Feliway) may help with inter-cat interactions.

If he is neutered it is a dominant behaviour rather than a sexual behaviour, in other words he is bullying her. you can try separating them during the night but there is no easy fix for such a behaviour.

Cats can exhibit mounting behavior of other cats and objects like pillows. The behavior is generally benign (there is not penetration) unless one cat bites the back of the neck too hard (this could break the skin an cause an abscess). Most cats will not tolerate this and will let the other cat know. Certainly stop the behavior is one cat is being bullied or there is a risk of physical harm. Some play behavior can also look like mounting (with mouthing, climbing on the other cat) but it's just wrestling. I hope this helps and please feel free to post any additional questions.

Socks and Prince are adorable! Thanks for posting pictures! Mounting behaviors are often dominance related and not sexual. So, since Prince has now reached sexual maturity at 6 months of age, Socks may be trying to make it clear to Prince that Socks is the more dominant cat. This can be a problem if it causes fighting, but is a normal behavior. The only solution I could offer you would be to have Prince (or both cats) fixed. And certainly if they are fighting with each other, then they will need to be separated. Good luck! I hope that was helpful. Thanks for using Petco Pet Education Center, formerly Petcoach.