A dog typically bleeds during the first phase of her heat cycle, called proestrus, which lasts about 7 to 10 days. This bleeding marks the beginning of the heat cycle and is usually blood-tinged discharge from the swollen vulva. The bleeding tends to lessen or stop during the next phase, estrus, which lasts about 5 to 10 days, when the dog is receptive to mating. Overall, the bleeding or bloody discharge usually lasts around 7 to 10 days but can vary between individual dogs, with some bleeding more heavily and others very little. The entire heat cycle lasts roughly 2 to 4 weeks

. In some cases, there may be lighter spotting or pinkish discharge that continues into the estrus phase, making the total duration of any colored discharge closer to 2 to 3 weeks, especially in first heats or larger breeds

. However, the most noticeable bleeding is generally confined to the first week to 10 days. Summary:

• Bleeding phase (Proestrus): ~7 to 10 days
• Total heat cycle: 2 to 4 weeks
• Bleeding amount and duration can vary by dog size, breed, and individual

If you notice irregular or excessive bleeding, consulting a veterinarian is advisable.