Female dogs do not have periods per se, but they do go through a regular heat cycle if they have not been spayed, or desexed.

The average heat cycle for a dog is anywhere from 1 week to 4 weeks in length. The time between heat periods is usually around seven months but can vary from every 4 months to once a year.

During the first part of the heat cycle, there is swelling and bleeding from the vulva, and male dogs will be hanging around nearby. This is what is generally thought to be a "period". The female will lick herself a lot more than usual, but blood spots may still be left around the house and territory.

Having your dog spayed will prevent this problem, and research has indicated there are health benefits associated with desexing. If you do not intend to breed your dog, having her spayed would be a sensible option.