While dogs don't experience menstruation the same way humans do, they do ovulate. And they'd probably appreciate a treat or two when they do.

By Lacey Howard
August 24, 2020
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Victoria Neer / Getty

When a female dog is in heat (called estrus), she has a bloody discharge from her vulva—similar to a human period or menstruation. But that’s where the similarities end. While humans experience a menstrual cycle every 28 days on average, dogs’ estrous cycle is six months or more. 

A dog’s heat cycle has four stages . The first three can span as much as 30 days and include times of:

  • bleeding (7–10 days)
  • receptivity to breeding  (7–10 days)
  • returning to normal  (7–10 days)

The fourth stage is the months between the end of one estrous and the beginning of the next. 

While the timing of the first heat varies by dog breed and size, a puppy can go into her first heat at as young as 6 months old. Unless she is spayed, she will continue to go into heat every six months or so well into her senior years.