tiny toy in heat

Question
QUESTION: I have a three year old tiny toy poodle (Phoebe) who has only been in
heat once and that was around her first birthday.  I own her mom, dad
and dad's mom.  Her mom is spayed now but she had very regular, every
6 months, heat cycle.  I have another female (also tiny toy) who goes in
heat about every 8 months but this doesn't seem to trigger anything in
Phoebe.  

I had wanted to breed her at least one time before having her spayed
because we wanted to keep her mom's line going but at this point it
doesn't look as though that will happen.

Is this normal?  Any suggestions?

Thank you!
ANSWER: She could still be having cycles and you are not seeing them because they are what we call silent heats.  You see no blood at all.  Usually the only way to know when a silent heater comes in is with a male smelling it.  There are tests that your vet can do to check to see if there are issues with her fertility.  The first test I would do is a thyroid test.  If her thyroid is low then she will be unable to become pregnant.  Yes there are drugs that can be given to help this BUT... you will be passing the problem on to the next generations.  If there is a problem in your line perhaps it would be best to spay the female and bring a totally new female in that does not have fertility issues.

---------- FOLLOW-UP ----------

QUESTION: Since I have a male dog who hasn't sensed her in heat since the first
time I have assumed she hasn't been having them.  Sounds as though
her grandmother on her father's side had silent heats but even in her
case males could tell.  

I always thought that females took after their mom's, is that true?

Sooooo . . .  (sigh) . . . it's to the vet for Phoebe!   You are right, I do NOT
want to pass this on to another generation.

Thank you so much!  

Answer
No its not true that they take after only the mothers.  That is genetically impossible since each parent contributes 50% of the genes respectivly.
If you male is not sensing it then I would be inclinded to think that she has a thyroid problem or other fertility issue.  I would rule the thyroid out first as it is a major factor and a little more easily diagnosed.  If the throid comes up as normal then you can go on to other testing to see what the problem is if you wish.