An intact male dog has a biological drive to make puppies. But, a male's success and interest is limited by their potential mate's reproductive cycle.
Canine Mating Habits
These days, domesticated dogs reproduce under the watchful eye of breeders and don't have to go to the same lengths as their ancestors or feral counterparts. After reaching puberty between six and 12 months of age, females will enter heat every six months. There are four stages of reproduction: anestrus, proestrus, estrus and diestrus. Anestrus is a prepatory phase lasting about two to four months. Following that, the "heat" cycle begins -- the cycle where potential mates start to take notice. Estrus marks the stage where the female is physically receptive to a mate and lastly, diestrus, a period of sexual inactivity follows.
Males Pursue Females in Proestrus
Proestrus is a period of time lasting anywhere between nine and 28 days when the female displays vaginal discharge, or "bleeding," and through urination, gives off a hormone and pheromone signal to males that she is seeking a potential mate. Males will cover great distances to vie for her attention during this entire time. When she allows mating, the estrus phase begins and she may mate with more than one male for a period of approximately four days. The males' pursuit of the female ends, until this cycle repeats itself -- a seasonal occurrence.
Males Move On
Males are receptive to mating at anytime and do not have a mating cycle per se. In domesticated species, females do all the parenting, leaving males to pursue other potential mates in the same manner. In contrast, wild dogs parent puppies as a team with all members of the group contributing to the caring of a single dominant male and female.
A male's desire to pursue a female is based on olfactory senses and he is able to smell the pheromones and hormones released in her urine from over a mile away. The more she "marks," territory, the more he will pursue. As this scent weakens through the reproductive cycle, he will turn his interests toward a more fertile potential. Neutered male dogs will not engage in this pursuit because their own hormonal urge to do so is non-existent.