
How long she was in for the first time is relevant because it is possible for a bitch to have a 'split season' especially to begin with, until things have settled down.
However, I did have just one, who came in bang on 6 months - unusual for my girls who all started at around 8 months, and cycled at that interval. She came from a mating that only produced her which may or may not have been relevant

. She was one that was quite a few generations into my breeding programme, with them all cycling at 8 monthly intervals. She then came in again 5 months later (the first was a full 21+ day season) and continued to do this for the few seasons she had. This I didn't need - not only was it pulling her down (phantoms), but it was also unnecessarily driving the males nuts

. In the end, as she really wasn't maturing into one I was very happy to show (she did go to a few early shows with some success) or to take a litter from, I made the decision to have her spayed which obviously sorted out all that every 5 months business!