Healthy Cat Rejecting Ill Cat

My 15 year old cat, Sunny, has Congestive Heart Failure. We have spent near $1000 on him so far. Thank goodness we had a medical credit card we where able to use because we don't have alot of money right now. Anyway, his sides are shaved. Sassy, our younger cat, will sniff his shaved sides, hiss, and run away. Now she mostly just avoids him all together. They used to be very close. Why is she doing this? Oh and the vet gave Sunny about 6 months to a year to live. It's incredibly sad but I'm glad I have some time to spend with him and get used to the idea he wont always be here. He has to take two meds a day.

Last night one of my cats, Leo, was injured (fractured leg) and now Roxy is doing just as you described... sniffing and then hissing, but she was so bold as to smack him on the face. But on the other hand, Taco hasn't left Leo's side except for to eat and use the litter box. He's been laying right next to him, keeping him warm and comforting him. I don't think I'll ever understand why cats do the things that they do.

I'm so sorry to hear about Sunny!

There may be a couple of things going on between your cats:

In their "native" environments, cats will often reject a cat that is old or in poor health. Cats live cooperatively and when one can no longer help with the group, they can be driven out. Also, Sunny was came from the vet and was shaved. He smells differently than before so Sassy might not fully recognize him right now. Give it a while and see if things change between them. If they don't reform their bond, give them ample space away from each other.

It could be survival instinct. In nature, old sick animals are rejected. That's why cats often hide that they are sick, cause of instinct.