Not totally sure, but I think the main reason you would wait until the 2nd heat cycle is to be sure the dog was mature enough. So, if she is 1 1/2 years old, then I would GUESS it was ok to breed. I think it's just the "average" that they cycle every 6-7 months, so that is why the rule-of-thumb is the 2nd or even 3rd cycle.
I could be totally wrong, though. |