The ability of female domestic dog to come into estrus at any time of the year and usually twice a year is also valued. The amount of time between cycles varies greatly among different dogs, but a particular dog's cycle tends to be consistent through her life. This is also called in season or in heat.
Conversely, undomesticated canine species experience estrus once a year, typically in late winter.
Becoming fertile (menarche)
Most dogs come into season for the first time between 6 and 12 months, although some larger breeds delay until as late as 2 years.Like most mammals, the age that a bitch first comes into season is mostly a function of her current body weight as a proportion of her body weight when fully mature. The different rates of maturation are responsible for the menarche, not the chronological age.
