when do female dogs get their first period
Some General Rules of Thumb for Canine Estrus. 1  The first estrus cycle usually occurs by age 6-12 months; for some small breeds, as early as 5 months, and for some large and giant breeds, the first cycle may not occur until 14 months of age or older. 2  On average, dogs have two cycles a year. The estrus cycle lasts on average 12-21 days, but maybe be as short as a few days to four weeks. The estrus period length varies widely between breeds and individual dogs. The length of a cycle varies widely, even for dogs of the same breed.