If the cats have been living together in peace and harmony for a while and are still doing so, I'd tend to look at the cat litter itself first as the potential problem. I remember my cat, Sylvester, got some really obnoxious chemical burns on the pads of his feet that were the result of the new-fangled clumping litter. Poor kitty. We didn't realize it until the vet asked if he had walked through something, and even then it took a few more days to figure it out.
We never did figure out why Sydney (his younger, adopted "sibling") started peeing in a corner all the way across the house. They had both been neutered at a young age, and Syd had already been in the household for two or three years before he began marking. By the time we noticed the scent, it was too late -- nothing could adequately break it down or mask it. Thoroughly soaked the baseboards. But Sydney was a very insecure kitty and very jealous of Sylvester when he got any attention at all. Ultimately, he found a new home (as the only pet) for a woman who had just lost her own cat to cancer. Our vet knew she wanted a replacement kitty. It was a fortunate relocation for everyone. ... But until that point, we tried just about everything we could to alleviate the problem.
Our current cat, Seven, is about the simplest-minded, most easy-going, friendliest, no-problem cat you could ever meet. (Although I dread the task of replacing our furniture some day and trying to teach her not to use the couch as a scratching post. Seven may have to lose her claws. We'll see.)
We never did figure out why Sydney (his younger, adopted "sibling") started peeing in a corner all the way across the house. They had both been neutered at a young age, and Syd had already been in the household for two or three years before he began marking. By the time we noticed the scent, it was too late -- nothing could adequately break it down or mask it. Thoroughly soaked the baseboards. But Sydney was a very insecure kitty and very jealous of Sylvester when he got any attention at all. Ultimately, he found a new home (as the only pet) for a woman who had just lost her own cat to cancer. Our vet knew she wanted a replacement kitty. It was a fortunate relocation for everyone. ... But until that point, we tried just about everything we could to alleviate the problem.
Our current cat, Seven, is about the simplest-minded, most easy-going, friendliest, no-problem cat you could ever meet. (Although I dread the task of replacing our furniture some day and trying to teach her not to use the couch as a scratching post. Seven may have to lose her claws. We'll see.)
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