Canine Reproduction


Canine reproduction is an area of veterinary medicine that has received relatively little attention in recent decades. Given the magnitude of the crisis of pet overpopulation and canine homelessness in this country (characterized by catastrophic mortality rates), it stands to reason we might choose to disavow this branch of veterinary science.

Despite the flagging popularity of this subject, it’s nonetheless important for dog owners to understand its fundamentals. After all, without a proper background in reproduction, we’re unable to make effective decisions about topics like sterilization, pregnancy, and reproductive disease, among others that might help us better understand and combat the dilemma of canine overpopulation.

The Basics

Bitch and dog are the proper animal husbandry terms for the female and male members of the canine species, respectively. They typically reach puberty between six and eighteen months of age, at which time a female’s first estrous cycle will commence.


Estrus is the 2-3 week period during which the female is said to be “in heat.” This is when she ovulates and becomes receptive to breeding. Estrus recurs every 6-18 months, with most young to middle-aged dogs tending to come into estrus more frequently than older bitches. Geriatric females will typically stop coming into heat (ovulating) completely.

The signs of estrus typically include more than one of the following:

  • Vulvar swelling

  • Increased frequency of urination

  • Increased activity level

  • Vaginal bleeding

  • Increased attractiveness to males

  • Increased receptiveness to male attention

Pre-breeding Exam

Ideally, both male and female and will be examined by a veterinarian in advance of breeding. The following tests and procedures may be undertaken as part of the pre-breeding exam:

  • Physical examination

  • CBC (complete blood count)

  • Chemistry (biochemistry screen)

  • Urinalysis

  • Sperm analysis for breeding males

  • Brucellosis testing for both males and females (see a related article on brucellosis)


Planned breeding takes place after measuring levels of progesterone once the female comes into heat or, less accurately, by examining the cells lining the vaginal wall (cytology).

Once that level of progesterone reaches an optimum level (or the cells take on specific characteristics if cytological examination is elected), females ovulate. At this time, they’ll become more receptive to males and breeding may ensue.

Among dogs and other canids, the mating process itself is relatively simple. A male will mount a receptive female, inserting a flaccid penis. A bone (the os penis) makes this intromission possible. Once within the vagina, the male’s penis will engorge. The male will subsequently dismount the female and remain in a position called “tying” until ejaculation is complete. At this point, the dog and bitch separate, and the process is concluded.

Dogs may mate many times for several days. Conception rates are considered very high among dogs. This is because of the extraordinarily long life of canine sperm (up to a week) and the unwillingness of most bitches to be mounted before they’re ready to ovulate.

Artificial insemination is also commonly undertaken in planned breeding settings. The conception rate after artificial insemination is significantly lower.


The gestation period for dogs is 63 days long. Early on, pregnancy can be detected by measuring levels of a hormone known as relaxin. From mid-pregnancy onwards, ultrasound may be used to confirm the presence of fetuses and assess their viability. Late in pregnancy, X-rays will reveal the bony structures of the fetuses. The static nature of X-rays allows veterinarians to determine the number of pups. 

During this period, pregnancy termination is feasible via routine sterilization of the female.


Whelping is the process by which pups are delivered. Most females are considered quite capable of delivering them on their own, without human intervention. Nonetheless, some females may require simple assistance in extraction of larger pups. Occasionally, veterinary intervention may become necessary.


Dystocia is the term veterinarians use to describe either an overlong gestation where whelping has been abnormally delayed or a delivery that isn’t progressing normally. This can happen for a variety of reasons. The following are the most common of these:

  • Pups are too big

  • Pups are not viable

  • Uterine inertia (uterus is not contracting normally)

Caesarian Section

C-sections are commonly required in veterinary medicine as a consequence of dystocia. They’re undertaken by way of an incision in the abdominal wall and then a uterine incision. In some cases, this procedure may be planned, as when pups have been determined to be over-large.

Breed Variations

Some breeds of dogs can mate traditionally while others may require assistance. Bulldogs and other breeds whose abnormal shape may preclude normal intromission of the penis and tying.

Brachycephalic (short-headed) breeds often require planned Caesarian sections. This is due to the abnormal shape and size of the pups’ skulls.


P.W. Concannon. Canine Pregnancy: Predicting Parturition and Timing Events of Gestation [PDF]. (Last Updated: 9-May-2000)

R.V. Hutchison. Elective Cesarean Sections: Risks, Planning, and Timing [PDF]. (Last Updated: 12-May-05)

K. Blendinger. Techniques of artificial insemination by fresh, chilled and frozen semen [PDF]. (Last Updated: 3-Jun-07)

S. Arnold, I. Reichler and M. Hubler. Canine Pyometra: New Approaches to an Old Disease. (Last Updated: 14-Oct-06)

Merck Veterinary Manual. Breeding Management of Small Animals.

Merck Veterinary Manual. Principles of Therapy Of the Reproductive System.