strange behavior

Question
Hello and thank you for a great website! We have started breeding chihuahuas after much research and thought. So far had one great litter and learned a lot. My question is twofold~  one of my bitches just finished her first heat and quite against our intentions was tied with our older stud dog. We will wait and see what happens but I am concerned that she may be too small to his slightly larger size. The other aspect is that one of my other bitches (due for second heat in June) is actually tying with this stud but she has no estrus  or discharge what so ever! What does this mean and should I stop them? I was quite suprised to see this and thought females only allow mating during estrus. Is this a split or silent heat? We're confused now! Thank you  for your answer~

Answer
When your bred small chi is twenty five to thirty days take her to the vet for an ultrasound to find out how many pups she has and their size and position. You'll need to monitor her to make sure she doesn't get into trouble.
Your bitch who is tying without estrus could be having a silent heat, or could have an infection that is making both her, and the male believe she is in estrus. Take her to the vet for a definite answer. You don't want to take a chance with infection. He should also be able to tell you whether it is a split or silent heat. I would check hormone levels as well.
Good luck
Cindi