The Heat Cycle of the Female Dog

dog nursing

Estrus is the period of sexual receptivity during the reproductive cycle, when a bitch will breed with a dog. It is important to be familiar with the signs of heat in your bitch, whether you are planning to breed from her or not.

At what age does a female dog first become sexually active?

The onset of puberty is extremely variable in dogs, and depends largely on the breed and size of the dog. While small breed dogs may have their first estrus cycle at 6 months, it may take as long as 2 years before a large breed dog shows any signs of estrus. On average the first season will occur between 6-12 months.

How frequently will the dog go into estrus?

Again, the frequency of cycling will depend on the particular breed of dog. The Basenji, for example, typically breeds only once a year. Seasons can occur every 4-12 months (on average). Owners usually become familiar with the frequency of their particular dog’s cycles. However, as the bitch gets older, she will tend to go into estrus less frequently.

What are the different stages of the reproductive cycle?

The reproductive cycle is made up of four phases: proestrus, oestrus, diestrus, and anestrus. The actual period of when the bitch is “in heat” is made up of the proestrus and estrus stages, and can last from 3-21 days.

Proestrus (lasts 9-10 days on average)

This is the stage preceding oestrus, when there are high levels of estrogen in the bloodstream. The bitch may begin to be attractive to male dogs, but will show little interest or even aggression toward males. The vulva may appear swollen and red, with a slight bloody discharge from the vulva – this is normal. Other signs that she is going into heat are restlessness, roaming, frequent urination, and licking her back end.

Estrus (lasts 5-9 days on average)

This is the period of the reproductive cycle when the female ovulates, and when she will accept male dogs for breeding. The female will crouch and elevate her hindquarters toward the male, with her tail moved to one side. The discharge from the vulva usually becomes a clear or straw-coloured mucus, and the vulva will appear more flaccid. The female dog may roam in order to find a mate, so it is important to keep her locked up.

Diestrus (last 9 weeks on average)

When the bitch enters this phase, she becomes unattractive to males. Dogs that do not become pregnant will have very high levels of progesterone circulating in the blood for 2-3 months. Dogs in diestrus can show signs of pseudopregnancy, or develop womb infections (pyometra).

Anestrus (last 3-4 months on average)

During anestrus, the levels of sex hormones in the dog’s bloodstream are at their lowest. This is a period of sexual inactivity for the dog.

How do I know when is the best time to breed my female dog?

Differentiating between proestrus and estrus is not always easy. You cannot reliably tell which is stage of the oestrus cycle a dog is in, based on her clinical signs. However, a veterinarian can identify the best time to breed the bitch based on two methods:

1. Vaginal Cytology: Swabs are taken of the lining of the vagina. The cells from these swabs are then examined under a microscope. The appearance of these cells changes from proestrus to estrus.

2. Progesterone Assays: Blood samples are taken daily or every day. The level of progesterone (one of the reproductive hormones) in the blood is an indicator of when the bitch should be bred.

How can I recognize if my dog has a false pregnancy?

Pseudopregnant dogs will show all of the signs of dogs that are actually pregnant. The mammary glands may enlarge, they can produce milk, there is abdominal enlargement, and they can show a number of behavioural changes. Common behavioural changes are nesting behaviour and trying to “mother” inanimate objects like socks or stuffed toys.

These dogs should be seen by a vet to determine that they are not actually pregnant. The condition usually spontaneously resolves in 1-3 weeks, although your vet may recommend treatment with cabergoline (e.g. Galastop). Dogs that have had false pregnancies tend to have them again, so it is suggested that they be either bred or spayed.

Is it possible to prevent my dog from going into heat?

There are drugs that can suppress the heat cycle. However, in most cases the benefit of the bitch skipping a season is outweighed by the many adverse side effects that occur with such drugs. Because of the serious health effects of drugs used to prevent heat, most veterinarians will suggest keeping the bitch locked up for the 2-3 weeks of her season, rather than risk her health.

Does a spayed female dog still show signs of oestrus?

No. Oestrus is induced by hormones circulating in the bitch’s bloodstream. When a female dog is spayed, the source of these hormones is removed, and thus she no longer comes into heat.  Many owners decide to have their animals spayed to avoid the inconvenience of having to manage the regular heat cycles of their female dog.

Can I get my dog spayed while she is heat?

Female dogs that are in good health can be safely spayed at any time, whether they are in heat or pregnant. Your veterinarian may suggest delaying the spay till after the heat cycle. The reason for this is that when the dog is in heat, the womb enlarges and the blood supply to the reproductive organs increases, increasing the possibility of haemorrhage.

(photo: robinelaine)