Just like all mammals, dogs have a distinct reproductive cycle that helps ensure successful mating. In female dogs, this is called going into heat. During this time, the female dog becomes fertile and receptive to males, and she excretes hormones that signal to males that it is time to breed. Females undergo significant physical changes during this time, making it very obvious that they are receptive to breeding. When they are not in heat, females will not tolerate breeding behavior and will rebuff a male's advances. In this respect, male dogs do not go into heat, as there is no set time at which they are receptive to breeding and there are no physical changes that are not directly related to the presence of a female dog that is in heat.
Male response to females in heat
If a male dog senses that a nearby female is in heat, he will generally show an increase in marking behavior. This means that even if he has previously been very well housetrained, he is likely to urine-mark walls, doorways and furniture, as well as outdoor features to which he has access. He may be responding to a female in his own home, or an unaltered male will also respond to female dogs in heat anywhere within his scent range. He may become agitated and repeatedly attempt to escape his yard in order to come in contact with the female.
Female response to males
When a female is not in heat, she will often be intolerant of a male's advances. She may snap or bite, and she will at least sit down at any mounting attempts. While in heat, however, she is likely to work harder at coming into contact with a fertile male. At his advance, she will stand and move her tail to the side, signaling to the male that she will accept him. It is important to note that after the initial bloody discharge, females are not out of heat-they are only just entering the fertile part of their cycle, and are most likely to become pregnant at this time.
Breeding responses in males
Upon encountering a receptive female, the male will generally fully assess the situation in terms of the female's scent and her likelihood of being receptive to him. Then he will mount her, and proceed with copulation. Unlike humans, a male dog needs no preparation for this act, as he actually has a bone inside his penis that allows for penetration at any time the female will allow it. Once coupled, it then swells in a manner similar to a human erection. The dog will be unable to pull free until copulation is complete, which may take anywhere from several minutes to an hour.
How to avoid mating behaviors in dogs
If you do not intend to breed your dogs, then the easiest way to avoid mating behaviors is to have your dog spayed or neutered as early as it can safely be done. In addition to avoiding the strong musky odor of a female in heat, or the aggravation of an excited male marking all over your house, the procedure can have many health benefits. Unspayed females are at risk of uterine infections, and both genders have an increased risk of hormone-dependent diseases such as some cancers. Breeding, especially when it's done too early, also comes with a wide variety of risks for your pet, and the puppies are a very time-consuming and expensive responsibility.