My adult male cats have always been suspicious of or even hostile to new cats regardless of the status of their reproductive organs. At present, I have two fixed males and one unfixed younger female, and their reaction was initially hostile to her. One is now very good friends with her, and the other started ignoring her completely after a month or so. It’s very important to have one litter box per cat, if you don’t already, and to give them time away from humans to establish their hierarchy.
Keep them seperated when you aren’t there to referee. They’re just establishing an pecking order. Older male will bully young female for a while. Eventually, they’ll either become friends or divide the house up.
Since he’s an adult, he could hurt her, if left alone before the sort it all out.
BTW, females are spayed, males are neutered. Spaying specificly means removing the ovaries.
Here is a little tip I learned when trying to do the same thing.
Put the kitten where the other cat can’t see it, but can hear it. Whatever you do, don’t let the big cat near the kitten for about 5 days. Cats are curious, he’ll be so anxious to find out what it is that he’ll be relieved.
It worked when we introduced a kitten to my mothers 10 year old male. They could sort of see each other under the door way and it drove the big cat nuts. They were great friends after that. Good luck.
My oldest cat, a neutered male, has been the adoptive “mother” of almost all the cats I have brought home ever since he became the oldest male. He licks them and lets them snuggle with them. He doesn’t play with them anymore though, he’s too old for that, which is why he wasn’t very tolerant of my second to last kitten that was a bit of a handful.
I believe he learned to be a mommy from a previous male cat who mothered him when he was a kitten. That cat probably learned this from my dog who treated him like one of her puppies. I do hear stories from other people that their male cats tend to be more motherly than females. So, I say it isn’t gender based but more a problem of getting the formerly only cat used to another cat in the house. Introduce them gradually and don’t force things.
Just reminds me of my own situation where we brought in a female kitten as company for our neutered male. He was inquisitive, but she reacted with surprising hostility and I’ll never forget the whunk! sound she made when he got too close and she flipped over in about 1.2 nanoseconds, hitting her spine on the hardwood floor and jamming all four feet toward him, claws flailing.