An adult male cat may bother a female kitten because it is trying to mate with it. The older cat may also attempt to establish hierarchy by displaying physical aggression, such as biting the back of the cat's neck, hissing or swatting at it. If you cannot get the male cat to leave the kitten alone through training and discipline, you might want to separate them or have the male cat neutered.
Have the male cat neutered. If the male cat and female kitten are unfixed and the male shows interest in mating, it will not stop until it has succeeded, even if the female does not show interest. The male cat will continue to seek opportunities to mate with the female, even if you interrupt its previous attempts. Getting the cat neutered will stop it from trying to mate and will decrease its overall aggression. It is a good idea to have the female kitten spayed as soon as possible.
Supervise the interaction between the two cats. Stay in the room or area where the adult cat and kitten are together. Be prepared to move the kitten away if the male cat begins to bother it. Distract the male cat with a toy or by playing with it. Be sure that each cat has its own toys and its own particular area to go to, such as a cat bed.
Separate the cats when you cannot supervise. This will be most useful if the adult is still adjusting to the kitten. Put the kitten in a carrier to protect it when you are not around. The adult cat will still hear the kitten and pick up its scent but realise it cannot get to it and may lose interest in bothering the kitten. If you do not want to put the kitten in a carrier for too long, shut one or both cats in a separate room or area so that the adult cannot access the kitten.
Discipline the male cat. Teach the cat that bothering the kitten is not acceptable behaviour. Use a strong tone and commanding voice to discourage the cat from bothering the kitten. You can also lightly tap it on the nose to show it that you are displeased.
Consider inside and outside placement. If the male cat continues to bother the kitten after you have temporarily separated them and disciplined the cat, then you may want to consider keeping one cat inside and one cat outside. If the male cat has never been outdoors before, then you might not want to suddenly change its environment. You may consider starting the kitten as an outside cat from an early age. If you do not want to keep either cat outdoors all the time, place one cat's food bowl and bedding in a separate area of your home, so that each cat has its defined territory.