Why are my neutered cats suddenly fighting aggressively for no reason?

It can take several weeks for testosterone levels to decrease after neutering. Until then, consider using a pheromone product, such as Feliway spray or plug in diffuser, to decrease any anxiety or aggression in the home. Provide extra litter boxes, bowls, toys and bedding to prevent food aggression or resource protection.

You should have him checked, or rechecked, by your veterinarian. Neutering typically does not result in more aggressive behavior. Additionally, any sudden behavioral change can be due to illness or injury. Once medical causes have been ruled out, you can focus on behavioral issues. Consider a pheromone product, such as Feliway Spray or plug in diffusers, to help decrease anxiety or aggression. Provide additional litterboxes, bowls, toys and bedding to prevent resource protection. You may have to separate them for a week or two then gradually reintroduce them while employing the measures described above.

That is unusual behavior so he may be irritable from being in pain. Outdoor unneutered male cats often fight and he may have an injury you can’t see which is painful. I recommend confining him to another room until he calms down so no one else gets injured, and see if he is eating normally. If this behavior continues please take him in for an exam to check for a wound or area of pain. In addition I would consider neutering him also. Neutered male cats seldom fight, they are more docile and less aggressive. Thanks for using Petco Pet Education Center, formerly Petcoach to help you care for Timmy.

Thank you for submitting your question regarding your cats. I suspect that the carrier ride and the surgery were stressful experiences for both cats. This can cause a cat to act out aggressively. You may want to keep the cats separate from each other for a few days to let them calm down. Then re-introduce them slowly and only when they can be fully supervised. Things should go back to normal between them, but it may take some time. I hope this information helps!

Have him examined by your veterinarian to diagnose illness or injury. Either are common culprits of a sudden behavioral change. Being an intact male may also be playing a role in the behavior. Consider having him neutered. In the meantime, provide additional food/water bowls, beds, toys and litterboxes to prevent food aggression or resource protection. Consider a pheromone product, such as Feliway Spray or plug in diffusers, to decrease any anxiety or aggression in the home.

I would recommend getting them neutered as soon as possible. As they have gotten older they are becoming more aggressive and controlling of there territory. I would recommend neuter, increase number litter boxes, increase food and water dishes to start. Hopefully once all the added hormones are gone they will settle down

I am sorry to hear about your concern for Tumbles! I would suspect he smelled another male cat's urine/marking which got him excited/worked up. If it becomes a routine issue you can consider using Feliway multicat products https://www.feliway.com/us/Products/FELIWAY-MultiCat-Diffuser