Monkey is 15 years old with arthritis, cancer (a tumor on his adrenal gland which has been operated on once last year to remove it, and has since returned), pancreatitis and kidney disease as a result of the medication required for the other ailments and well... just because he's a cat.
At the end of last year, we decided to adopt a rescue kitten (Audrey) from our Cat Clinic in the hope that it would give Monkey an extra lease on life and some company. The initial introduction period was about as you would expect, but within a month they were getting on pretty well. They would play together and were quite comfortable in each other's company about 90% of the time. Some days when Monkey wasn't feeling great, he was crankier than usual with Audrey but never did more than hiss at her and give her the occasion swat around the ears if she wanted to play and he didn't. He never took it any further than that. (He was desexed years ago, at 3 months old)
Last week she was desexed and since she came home he just will not leave her alone. He stalks her around the house constantly and I've caught him mounting her several times in the last few days. Today I heard her crying out (and she usually doesn't meow much at all unless it's dinner time) and when I ran into the room to see what was happening, she ran out and Monkey was right behind her. I can only assume he was at it again. I separated them after that, and have been keeping them in different parts of the house and will shut her in the study tonight so he can't have another go at her while we're asleep.
He is relentless though, and it's only been since she came home from being desexed. Is this something that can commonly happen with an older male cat and a young female? Is there anything I can do to make things go back to how it was between them before? It has been 2 months since she came to live with us, so they had over a month of really good progression in co-habitation. She actually doesn't seem overly concerned about it or didn't until today when I heard her crying out.