Female dogs usually go through sexual maturity at around their sixth month, with smaller breeds going into heat earlier than their larger counterparts—some of the extra-large breeds may not go through a heat cycle until they are around age two.
A dog’s heat (oestrous) cycle usually lasts between two to three weeks, and is bookended by the start and finish of vulvar discharge. On average a female dog will go into heat twice per year (roughly once every six months), and become more regular as the dog ages. Smaller breeds tend to have a larger number of heat cycles per year, as many as four, where larger breeds may enter heat cycles once every twelve to eighteen months.
Signs that a Dog Is Entering a Heat Cycle
The most obvious sign of an oestrous cycle is vaginal bleeding; however, the bleeding may not happen or become noticeable a few days after the start of the heat cycle. Increased licking of the vaginal area, and generally paying more attention to it are good indicators; however, the first sign that a female has come into oestrus will be the swelling of the vulva.
Males will be drawn to a female in heat from the start of the heat cycle; however, females generally don’t allow mating activities until well into the cycle (usually around 6 to 10 days), around the time when there is only minor presence of blood in the vaginal discharge.
If you notice heavy vaginal bleeding, it would be advisable to seek the advice of a veterinarian to rule out any complications, though usually it will just be an abnormality for some dogs.
When is a Female Dog Fertile?
As a rule of thumb, a female dog will usually become fertile twelve days after the bleeding starts, which is around the time when it slows down and can only be noticed as a pinkish color. If you are trying to mate dog, it will be required to check with your veterinarian in order to determine when she is fertile, unless of course the sire with which she is to mate is on hand—he’ll be able to tell when she is ready by licking and evaluating her readiness.
Diestrus & Anestrus: The Heat Cycle Winds Down
The third phase of a dog’s heat cycle is called diestrus, and it can last from 50 to 80 days. This phase will begin whether or not a dog has become pregnant (or even if she has not been mated). During this time, the dog’s body will show signs of pregnancy despite not being pregnant, and she will not accept male advances.
The diestrus is followed by the anestrus (the fourth and final phase), which lasts between 130 to 250 days. During this period the body rests in preparation for the next heat cycle.
During a heat cycles, it is important to understand the intense desire by the dog to mate, which may result in escape attempts. So keep an eye on her and make sure she is safe, and doesn’t end up getting lost and end up with an unwanted pregnancy.
