Sudden aggression towards brother

Hi, im Dan, im new to this forum but after reading a few threads it seems very helpful indeed.. i hope someone can offer me some advice ..

I have a problem with my 2 kittens..

They are brothers, aged 23 weeks. Up untill now they have both been kept indoors, but get on absolutley fine together, spending their days eating, playing and sleeping (at times) pretty much on top of each other. They are almost inseperable.

Yesterday they were both spayed, and to my pleasant surprise they seemed to take it in their stride and were both fine when they got home.

The vets told us it was fine to allow them outside so today they we let out for the first time, for about a hour or so. Murphy (the slightly smaller one) was out in the garden like a shot, exploring and having fun. Sid (the larger one) on the other hand had a few steps outside but didnt seem interested and stayed inside.

However, now they are both settled back indoors, Sid flairs up, hisses and flashes his teeth whenever Murphy comes near him - something he has never done before.

This just seems such strange behaviour and totally out of charactor as they are normally so close.

Any advice about this behaviour would be brilliant

Thanks in advance!

Sid may be associating Murphy's scent with that of the Vet or possibly Murphy came into contact with something outside which has effected his scent. You may want to consider a Feliway diffuser. You may also put a dab of pure vanilla extract on each of them under their chin, between their shoulders and at the base of their tail several times a day, giving them the same scent. I would also wonder if Sid is exhibiting this aggression because he is feeling poorly.

thanks very much! Sid is showing no other signs of being ill and he was given a look over from the Vet just 2 days ago, so i dont think thats the problem. I will go and try the vanilla extract idea now! - fingers crossed!!

Hi Dan, I'm also new to this forum and have seen our cats act like that towards their littermates. I assumed it to be the action cats take to determine who will be alpha male. None of my cats has ever been seriously injured, I hope this is your case as well.

Maybe Sid feels the need to use aggression on Murphy to secure his position in the household?