
Hi, A bitch's seasons last for an average of 21 days, roughly twice a year. She won't be fertile for all of that time, but you can't take any chances and she needs to be kept away from male dogs for the entire period. Some bitches get a form of PMT, others don't (much like people, really!), and most will get a phantom pregnency to a certain degree after the season....some hardly notice, some poor bitches go through hell.
Hope this helps.
:)