Shih Tzu First Estrus

Question
My female Shih Tzu puppy was whelped 3-8-07.  My neutered grown male Shih Tzu is suddenly very interested in her. I don't notice any discharge from the female.  It's my intention to have her spayed. Questions:  Is she in heat?  Isn't it too soon for her to be in heat?  When can I have her spayed?  Why does my neutered male exhibit sexual tendencies?

Answer
females usually begin first heat cycle between 6 months and 1 year of age they can sometimes have a earlier cycle a puppy heat with some swelling etc.  You can have your little girl spayed right now any time before her heat cycle preferred!  Your male is probably not really interested in her as much as in a sexual way as he is in a dominance way animals exhibit the behavior of "humping" to show dominance and rank over others.  He is basically letting her know that although he may have had surgery he is still "the man" of the pack .. so to say... once she rolls over and becomes submissive or he plain wears tired it will be over.  But you can have her spayed and not worry about the heat mess to come.. and let things get back to some normalcy at home.
Hope this all helps and best of luck with your Tzu family.