My neutered male cat often mounts my spayed female and thrusts. Are they really having coitus, or is this just a common behavior?
There are a few reasons that this can happen. When a tom is neutered about 90% won't display tom behaviors anymore. However, in about 10% of the cases they continue the behavior although they can't reproduce.
There are the cases of the cryptorchid cats that could come into play...read this: Cryptorchid Cat .