Normal Heat Cycle
A “heat” refers to the time when a female dog becomes sexually responsive to a male dog in attempts to conceive a pregnancy. Most female dogs will demonstrate signs of their first heat sometime after she is 6 months old, with smaller dogs tending to start earlier than larger dogs.
Most dogs will have a heat cycle routinely every 6 to 8 months, with the heat lasting on average a total of 14 to 20 days. During this time frame it is normal to see a bloody vaginal discharge for the first 7 to 10 days. The female may not necessarily ovulate, or release the eggs, until this bleeding subsides. It is during this period when she will typically allow a male dog to breed her.
If successful, a pregnancy will last 60 to 63 days from the mating, although the time will vary depending on when the actual ovulations and fertility occurred.