Estrous Cycles in Dogs

When does a female dog have her first estrous (heat) cycle?

Female dogs will have their first estrous (reproductive or heat) cycle when they reach puberty. Each cycle consists of several stages; the stage called estrus refers to when the female can become pregnant. Often, a dog that is in the estrus stage is said to be in heat or season.

On average, puberty (or sexual maturity) is reached at about six months of age, but this can vary by breed. Smaller breeds tend to have their first estrous cycle at an earlier age, while large and giant breeds may not come into heat for the first time until they reach eighteen months to two years of age.

How often does a female dog come into heat?

Most dogs come into heat twice per year, although the interval can vary between breeds and from dog to dog. Small breed dogs may cycle three times per year, while giant breed dogs may only cycle once per year. When young dogs first begin to cycle, it is normal for their cycles to be somewhat irregular. It can take up to two years for a female dog to develop regular cycles. No time of year corresponds to a breeding season for domesticated dogs except for Basenjis and the sled dog breeds, which typically tend to cycle in the spring.

What are the signs of estrus?

The earliest sign of estrus is swelling or engorgement of the vulva, but this swelling is not always obvious. Bloody vaginal discharge is often the first sign that an owner notices when their dog comes into heat. In some cases, the discharge will not be apparent until several days after estrus has begun. The amount of discharge varies from dog to dog.

"Male dogs can detect a female in heat from a great distance..."

The vaginal discharge will change in color and appearance as the cycle progresses. At first, the discharge is very bloody, but it thins to become watery and pinker in color as the days pass. A female dog in heat will often urinate more frequently than normal or may develop marking behavior in which she urinates small amounts on various objects either in the home or when out on a walk. During this phase of her cycle, the urine contains pheromones and hormones, both of which signal her reproductive state to other dogs. This is how dogs in heat attract other dogs, particularly males.

Male dogs can detect a female in heat from a great distance and may begin marking your property with their urine, attempting to claim their territory.

How long does estrus last?

Although it can vary by individual, the average length of the estrus stage is 10-14 days.

At what stage of the estrus cycle can the dog get pregnant?

The female dog usually ovulates at about the time that the vaginal discharge becomes watery; this marks her most fertile stage and is the time when she will be most receptive to breeding. However, sperm can survive for a week in the reproductive tract and still be capable of fertilizing the eggs, so she can get pregnant at any point while she is in estrus. Contrary to popular belief, it is not necessary for the female to tie with the male dog to get pregnant (for further information see the handout "Estrus and Mating in Dogs").

How long does pregnancy last in a dog and when can pregnancy be detected?

Pregnancy in dogs lasts approximately nine weeks (63 days).

How can I prevent my dog from becoming pregnant?

The best way to prevent your dog from becoming pregnant is to have her surgically sterilized (spayed) by ovariohysterectomy or ovariectomy before she has her first estrous cycle. Since it can be difficult to predict when this first cycle will occur, most veterinarians recommend performing the procedure before the dog is six or seven months of age.

What can I do if my dog has been mismated or accidentally mates with another dog?

Contact your veterinarian as soon as possible. There are mismating injections that can be used within the first two days after mating, but there are risks associated with their use. Your veterinarian will discuss your options and any risks associated with them.

Should I let my dog have an estrus cycle or a litter of puppies before spaying her?

"...the consensus at this time is that spaying will increase the lifespan of a dog."

There are no valid reasons for letting a dog have a litter of puppies before she is spayed. Newer research has shown that some larger breeds (e.g., Labrador Retrievers, Golden Retrievers, and German Shepherds) may benefit medically from delaying their spay surgery until after their first heat cycle; however, the consensus at this time is that spaying will increase the lifespan of a dog. Dogs can become pregnant on their very first estrous cycle, increasing the risk of accidental breeding. Dogs are indiscriminate, so a brother may breed with his sister, a father may breed with his daughter, and a son may breed with his mother.

A common belief is that female dogs will become more friendly and sociable if they have a litter of puppies. This is not true and only serves to contribute further to the serious problem of dog overpopulation.