Bringing cat home after Vet stay

Question
Hi Tabbi,

I have two feral cats that I adopted from the SPCA a year ago.
The youngest recently became VERY ill with an inner ear infection that eventually spread to his chest causing pneumonia.
He was at the vet's for about 4 days, being given an IV since he was dehydrated, as well as many antibiotics. We just brought him home today and the older brother is acting quite aggressive towards him. He hissed at him (Something I've NEVER heard him do period!), and just won't have anything to do with him whatsoever.
It's breaking our hearts to see this since all his little brother wants is some affection from him. These two have an incredibly close bond, so seeing this sort of aggressive behaviour came as quite a shock to the both of us.
I understand that he smells different due to being at the clinic for several days, and knew that the older one would have some issues with that.
What I would like to know is how we can help this along, as well as how long this may be before the older boy becomes affectionate towards his brother once again.

Thank you in advance for your help!

Answer
Lily,

That is normal behavior towards cats that come home from the vet. Cats go by smell and not by sight in recognizing other cats (with humans, they go by voice...not by sight). Your cat brought home MANY different smells from the vet: anesthetic, medicinal smells, and smells of other cats...all clinging to his fur and skin. The brother thinks he's another cat because he doesn't smell the same! Things will settle down  when the smells are gone from the spayed female.

As the cat grooms himself he will be replacing his regular scent. You can keep them separated if you want until the smells are gone from his fur. It will take a few days.

You can also rub the cat who did not go to the vet with a towel, then rub the cat who did go to the vet with the same towel to transfer familiar smells but do not do it the opposite way because you will then be transferring the vet's office smells to the other cat.

A trick that I've heard a lot of people use in that situation (though I have never tried it) is to put a drop of vanilla on each cats forehead so they smell the same.

Try giving both cats a special treat, like a can of tuna. Feed them next to each other so that being together is a pleasant experience and not a negative one.

You can try a popular cat calming spray and plug-in called Feliway, or Comfort Zone with Feliway. It is available at pet stores like PetSmart, Petco, etc., a vet's office (they use it too), or on-line. It copies relaxing pheromones that cats produce from rubbing their faces on things.

There is also another cat calming product that you can add to her food or water that reduces anxiety called Bach's Rescue Remedy. It is available on-line and in health food stores. Here is a link about it: (copy and paste, or type the whole links into your address bar)
http://www.bachflower.com/Pets.htm

Things will settle down once the smells are gone from the cat that went to the vet.

Tabbi