A dog’s period, or estrus cycle, is a stage in the reproductive cycle where a dog can become pregnant. When a puppy gets her first estrus cycle, as well as the frequency or her cycles, depends on her size and breed.
A puppy has her first estrus cycle when she reaches sexual maturity, or puberty. On average, this occurs between 10 and 12 months of age. However, the breed and size of your dog play a role in sexual maturity. Smaller dog breeds, such as Chihuahuas, reach puberty and estrus as early as 6 months of age. Larger dog breeds, such as Newfoundlands, may not begin estrus until 18 to 24 months of age. The normal range of initial estrus is anywhere between 6 and 24 months.
Frequency of Estrus Cycles
On average, your unsprayed female dog begins an estrus cycle every six months, or twice a year. During the first two years, your dog’s cycles may not come in regular intervals, as it takes some time for the body to develop and cycle. Breed and size can also play a role in estrus frequency. Smaller breeds may have up to three estrus cycles a year, while larger dogs may only have a cycle every 12 to 18 months. On average, a complete estrus cycle lasts 18 days.
What Occurs During Estrus
As estrus approaches, your dog’s hormone levels begin to change. Early symptoms of an estrus cycle, and especially the first cycle, may not be noticeable. You may see slight behavioral changes, such as nervousness, alertness and an increase in urination frequency. During this initial stage, the external vulva swells. Within a couple of days, a bloody vaginal discharge begins. This discharge typically lasts for seven to 10 days before changing to a clear discharge. When this discharge changes to a clear appearance, your dog is able to become pregnant.
Spaying Before Puberty
If you do not plan to breed your dog, spaying should take place before puberty and the first estrus. In addition to reducing accidental pregnancy and dealing with estrus cycles, spaying reduces the risk of breast and other reproductive system cancers. Contrary to previous beliefs, waiting until after the first heat cycle to spay does not provide any health benefits -- it actually increases the risk of breast cancer. Spaying can occur as early as 2 months of age. Talk to your vet about the best time to spay your pup.