A female dog goes into heat again between 4 and 6 months of having her puppies. The non-spayed dog goes into heat twice a year, and this is known as estrus.
The estrus cycle lasts between 12 and 21 days but often varies between breeds and dog size. The cycle can last for only a couple days, or it can continue for up to an entire month. While dogs can conceive during their primary estrus cycles, it is not recommended. A young dog is not fully mature, and a pregnancy in a 6-month-old or younger dog has the potential to lead to complications for both the mother and her puppies.