How long do dogs have their period?

Female dogs spend 2 to 3 weeks in heat and a bloody discharge is present only for the first 10 days, says VCA Animal Hospitals. The bloody discharge fades to a clear or watery discharge as the heat cycle progresses.

Female dogs go into heat twice a year, says the ASPCA. The organization recommends spaying female dogs before they enter their first heat if the dogs are not intended for breeding. There is no benefit to letting a dog experience heat before spaying, claims the ASPCA. Veterinarians at the VCA Animal Hospitals suggest surgically sterilizing female dogs at 6 or 7 months old.