My old girl Chelsea who is 16 was spayed a long time ago probably when she was about two. Although no physical signs she is behaving like a bitch on heat, giving off pheromones and making up to Parker my dog. It is really funny to watch this very old girl behaving like an adolescent. I am not sure how long to let this go on for? At the moment I am having to keep Parker in a separate room, being rather frail an accident with Parker may cause her some injury. Ever since she as spayed at two she has never shown any signs of being in season.