In female dogs, they reach puberty by 6 months upto 2 years depending on the breed of the dog(small or large).A dog puberty has 4 phases-proestrus(on an average lasts for 9-10 days), estrus(on an average lasts for5-9 days), diestrus(on an average lasts for 9weeks), and anestrus(on an average lasts for 3-4 months). Now the actual period of when the bitch is “in heat” is made up of the proestrus and estrus(period of sexual receptivity during the reproductive cycle, when a bitch will breed with a dog) stages, and can last from 3-21 days. The frequency of cycling will depend on the particular breed of dog. Seasons can occur every 4-12 months (on average). You can come to know if your female dog is in heat by the following symptoms mainly restlessness, roaming, frequent urination, and licking her back end. No female should be mated before the age of 1 yr minimum and the whelping time is about 63 days.