Unlike other species, the heat cycle of canines does not seem to follow any logic such as following a specific seasonality or temperature change. Rather, it just occurs regardless if it is the dead of the winter of the dog days of summer.

Many times the dog's heat cycle, better known as estrous cycle, seems to be quite unpredictable. The first heat generally occurs around six months in small, medium dogs and around 12-18 months in larger breed dogs. However, It is not unheard of some giant dog breeds going into heat at around 30 months of age.

 

Phases of the Dog's Heat Cycle

The cycle is divided in four distinct phases.

• Proestrus

This is when the dog's reproductive tissues swell and appear puffy. A bloody discharge will take place as the female carefully licks herself quite often in order to keep herself clean. Loss of appetite and irritability are not very uncommon. Male dogs may be interested in the female but she will not be interested as of yet. This phase generally lasts seven to ten days.

• Estrus

This is phase is also known by breeders as ''standing heat'' because this phase is actually when the female dog will stand still for the male to breed. Gradually the bloody discharge seen in proestrus will be replaced by a pink or straw colored discharge signaling this important phase. This phase generally lasts six to ten days.

• Diestrus

This phase concludes the mating process, as most females at this point will no longer be interested in males. Males however, may still stick around. This phase if the dog has been impregnated lasts generally from the end of the estrus until the birth of the puppies, averaging therefore 60 days. If the dog has not been impregnated, the diestrus phase will not be any different from the anaestrus stage.

-Anaestrus
This is the longest phase of a dog's heat cycle, indeed it ranges from 100-150 days. It appears to be a quiet time for the dog's reproductive organs, however, the dog's pituitary gland an ovaries are in reality getting ready for the next proestrus cycle.

 

 

Heat Abnormalities

• Split Heat

In this case, the dog's heat is interrupted and then continued at a later time. Basically a female dog will exhibit signs of pro-estrus with the typical bleeding but then once estrus approaches the symptoms disappear for some time.

• Induced Estrus

It appears that in some cases, the presence of a female in heat may awaken the heat cycle as well in other females.

• Silent Heats

In this case, the heat is silent, meaning that there are hardly any outward signs suggesting that the heat has occurred.

How Often does a Dog come into Heat then?
Most dogs generally go into heat every six months...,  twice a year. 

 

Breeding Difficulties

-Picky Females

While males seem to have no problem breeding with the female in heat, females on the other hand may be selective at times.

-Multi Sired Pups

If the female dog is allowed to escape she may breed with various males, often causing what is known as ''multi sired litter'' where there are puppies from different fathers.