Neutered brothers/mating season?

I adopted two seven year old neutered males (brothers from same litter) six months ago, from a widow who could no longer look after them. Both cats gradually adapted to their new home and everything seemed to be going well. They are mostly house cats, who sometimes go out onto a patio to nibble on grass. Neither cat showed any aggression towards each other, often play chasing around the house and sharing night crazies. The dominant cat always seem interested in the "rear end odors' of his brother, by often sniffing at the anus.
Two days ago, he became quite aggressive in his sniffing approach, to the point that the sibling began to hiss and snarl at him, eventually ending with the subordinate cat running away, chased by his dominant brother. Now the subordinate cat stays in hiding... his brother is stalking him when ever he leaves his hidout. The behaviour of the dominant brother is very similar to mating behaviour I've witness when a tom is singleminded on pursuing a female in heat. He has the same look, when eyes are fixed on his brother.
What is the solution? In order to give the subordinate cat some peace, I will seperate them for several hours at a time. One cat in the house, the other on the patio with me.

Awwww, I am not sure really...

Hopefully someone will be by to help you shortly..and I am sending lots of good luck that you can get it figured out

Maybe he smells different from being outside so your other cat doesn't recognise him. Or he may be sick, cats can smell illness on other cats.

Originally Posted by missymotus

Maybe he smells different from being outside so your other cat doesn't recognise him. Or he may be sick, cats can smell illness on other cats.

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I agree with these ideas. Were they accustomed to going out at their previous house? Even if they were, there could be some stray cat smells that they are picking up outside at your place. Cats are so sensitive to that type of thing.

If it goes on much more, I would seriously consider taking the victim to the vet to get checked over. He could be letting off an odd smell from being ill, like missymotus said.

there could be a female cat in heat outside. all my males except one who is 5 months are neutered , but when we had a female go into heat after she had a litter of kittens the house went mad, the females were fighting and moaning at each other (all spayed) the males were fighting and still trying to mount the female who was in heat so i had to seprate them even though they couldnt get her pregnant they still had an urge. i think it just upsets the blanace in the house. you could try a freliaway SP? plug in or spray. that might help calm things back to normal.

I am not aware of any other cats in the neighborhood that are wandering around free. Prior to me taking over these cats, they had never left their previous house.
After more observation, this may be jealousy. The dominant brother was the most friendly, affectionate and the first to accept his new surroundings. The other remained recluse and shy for about six weeks after his brother "came out". When the subordinate brother finally emerged and became comfortable with his new surroundings, he became very vocal, as if demanding attention, which he received. Things settled down for about three months, without any animosity. In the several days before this episode, the subordinate probably received more attention than his brother.
The subordinate brother is now so afraid of his sibling that all the dominant one has to do is show himself, walking towards him with purpose and the other runs away and hides.
If this is indeed jealousy... any suggestions? The subordinate brother is quite stressed out. They do not actually fight at this stage. When it first started they did trade a few harmless paw swipes, but once the dominant one reasserted his dominance, they was no more of that.

Might be the possiblity that one or both of them at one time DID breed and still remembers. I'd try a bit of vanilla extract on their noses/butts to help them calm down.

There could be a female in heat in the neighborhood that is triggering the response. Keep them inside for a few weeks so that they forget whatever is out there.