Age male is fertile

Question
My female and my daughter's male shih tzu (also my female's son)were together for 5 minutes without supervision and got locked.  He is 5 1/2 months old.  Can she be pregnant?  Is he fertile?

Answer
A male shih tzu is fertile at around 6 months of age, so it is  highly possible that your boy is shooting live ammunition.  And a tie means that it was a breeding of success.  You will need to take her to the vet and inform him of the situation and decide what steps should be taken.  You do not want to have a litter of puppies from a mother/son relationship.  Whenever you have a female in heat always keep her kenneled or never allow un-neutered males to visit unless it is a planned mating.  Hope things work out for you. Maybe, just maybe he was shooting blanks...