A complete discussion of breeding and reproduction in dogs is beyond the scope of this website. And considering the surplus of pet dogs in the US and other countries, casual rearing of litters by pet owners is not recommended. However, the following section includes a basic discussion of reproduction in dogs.
Dogs can be bred naturally or artificially. Artificial reproduction techniques include insemination with fresh, chilled, or frozen-thawed semen. Because male dogs are more likely to breed successfully in their home environment, females are generally taken to the male rather than the reverse.
Female dogs usually have estrous cycles twice a year, but the interval between cycles can range from 4 to 13 months. The average interval between cycles is 7 months, but some large breeds (for example, Great Danes) may cycle normally every 9–12 months. The anestrus phase is the nonbreeding portion of the cycle and is marked by inactive ovaries and a small uterus. A female dog in this phase is not attractive to male dogs and will not allow them to mount. The end of anestrus is marked by an increase in luteinizing hormone and follicle stimulating hormone. Anestrus normally lasts 1–6 months.
During the proestrus stage, female dogs become attractive to males but still do not allow them to mate. A bloody discharge from the vagina can be seen and the vulva starts to enlarge and becomes firm. Blood levels of the hormone estrogen rise during proestrus. In most dogs, proestrus lasts about 9 days (with a range of 2 days to 3 weeks).
During estrus, female dogs are receptive to breeding by males. At this point estrogen levels are declining and progesterone levels increase. The amount and consistency of vaginal discharge varies between dogs, but it may decrease and become straw colored during estrus. The vulva becomes soft and "wrinkly" as the dog nears estrus. Estrus can be as short as 3 days or as long as 3 weeks, but is about 9 days long on average. Ovulation occurs during estrus, about 2–3 days after luteinizing hormone levels peak. Dogs ovulate even if they are not bred (a process called spontaneous ovulation).
During the last phase, diestrus, female dogs again become resistant to breeding by males. Vaginal discharges diminish, and the vulva begins to slowly shrink in size. The uterus enlarges due to stimulation by progesterone. Progesterone levels increase during the first half of diestrus, then slowly decline. In dogs that are not pregnant, diestrus usually lasts for about 2 months. If the dog becomes pregnant, progesterone levels stay high and the pregnancy lasts for about 62–64 days.
Timing ovulation can help to accurately determine the length of pregnancy and expected date of delivery, evaluate infertility, optimize litter size, and plan breeding. Veterinarians can help time ovulation through the use of physical examinations, hormone testing, and by evaluating cells taken from the vagina (called vaginal cytology). Discuss breeding with your veterinarian before your dog comes into season. Then, notify your veterinarian as soon as you notice evidence of heat, such as vaginal discharge, swelling of the vulva, or attraction to male dogs. Your veterinarian will examine your dog and take appropriate blood or vaginal samples, usually every 2 days. Based on these results, your veterinarian will recommend which days are appropriate for breeding.
Artificial insemination is becoming more common in dogs. Veterinarians can collect semen from males and then deposit it into a female during the appropriate time in her cycle. The semen can be treated so that it can be shipped and used at a distant location or used at a later time. It can also be frozen for longterm storage.
Unlike in other domestic species, manipulation of the estrous cycle is not easy in dogs. Prevention of estrus is typically accomplished by spaying, although short-term suppression of estrus can also be achieved by medication. Side effects of medical suppression can include inflammation of the vagina, changes in the skin and liver, and birth defects in female puppies. It is also possible to use medications to speed up the onset of estrus in dogs that are in the late anestrus phase of the cycle.
Unplanned and unwanted mating of dogs is a common concern. Pregnancy can be completely prevented by spaying or neutering. Pregnancy can also be ended by having your veterinarian give a synthetic prostaglandin or the corticosteroid dexamethasone. The pregnancy should be confirmed before treatment, because 60% of misbred dogs do not become pregnant.
Pregnancy in dogs can be detected by physical examination (palpation of the uterus) at about day 21 of gestation. A blood test is also available that measures the hormone relaxin and can detect pregnancy by day 30 to 35 of gestation. The developing fetuses can be seen on x-rays after about day 45. X-rays taken more than 55 days into pregnancy are the best way to determine the litter size. Ultrasonography can reliably detect pregnancy by 25 to 35 days and also allows your veterinarian to confirm that the fetuses are alive.
Pregnancy lasts about 62 to 64 days in dogs, but predicting the timing of delivery can be difficult because the date of breeding does not always match the date of conception. The length of pregnancy can also vary with breed and litter size. A drop in rectal temperature usually precedes delivery by about 8 to 24 hours.
Labor and delivery in dogs is divided into 3 stages. Stage I lasts 12 to 24 hours. During this stage uterine contractions begin, but are not visible externally. The cervix also begins to dilate. Dogs may show behavior changes (such as becoming restless, nesting, hiding), refuse to eat, vomit, pant, or tremble during stage I. They may also have clear, watery discharge from the vagina. During stage II, abdominal contractions can be seen and the puppies are delivered. The puppies are usually delivered at intervals shorter than 1 to 2 hours, but that can vary considerably. Stage II can last up to 24 hours, but normal delivery is typically shorter. Stage III is defined as the delivery of the placenta. Dogs typically alternate between stages II and III until delivery is complete. A placenta should be delivered for each puppy, but they are not always delivered together.
Abnormal labor and delivery (dystocia) can be diagnosed if the uterine contractions are too infrequent or too weak to deliver the fetuses. This can lead to prolonged labor (more than 24 hours for stage I, more than 12–24 hours for stage II, or more than 1–4 hours between delivery of puppies during stage II). Other signs of difficult birth include puppies that are born dead or near death or excessive maternal distress. Uterine and fetal monitors can be used to assess the condition of the uterus and fetuses. Dystocia can be treated either medically or surgically. Medical treatment includes injection of calcium and/or the hormone oxytocin to increase the strength and frequency of uterine contractions. Neither should be given without the specific advice of a veterinarian. If these measures are not successful, cesarean section is performed to remove the fetuses.
Physical examination, and in some cases x-rays, are used to ensure that all puppies have been delivered. Post-delivery injections of oxytocin are not routinely given unless the dog has not delivered all of the placentas. The mother's body temperature, vaginal discharge (lochia), and milk should be monitored. Normally, the lochia is dark red to black and is heavy for the first few days after delivery. It is not necessary that the mother eat the placentas. Disinfection of the umbilicus (belly button) with tincture of iodine helps prevent bacterial infection in the newborn puppies. Puppies should be weighed as soon as they are dry and then twice daily for the first week. Any weight loss after the first 24 hours indicates a potential problem and should be given immediate attention, such as extra feeding, assisted nursing, or examination by a veterinarian (see Puppy Care). Newborn puppies should gain 10% of their body weight each day.
Dogs should be allowed to deliver their puppies in a familiar area where they will not be disturbed. Unfamiliar surroundings or strangers may hinder delivery, interfere with milk letdown, or adversely affect maternal instincts and cause the dog to neglect her newborn puppies. This is especially true for a dog delivering her first litter. A nervous dog may either ignore the newborn puppies or give them excess attention. This can lead to nearly continuous licking and biting at the umbilical stump, which can potentially cause serious injury to the puppy. If the dog’s maternal instincts fail, she may lie down in an upright position that does not allow the puppies to nurse, or she may leave the puppies unattended.
Following delivery and because of the demands of nursing, calcium levels in the bloodstream of the dog may fall to abnormally low levels. This problem is most common in dogs weighing less than 45 pounds (20 kilograms) and may be worsened by an improper diet or a very large litter.
Common inflammatory diseases in the period after delivery include inflammation of the uterus (metritis) and breasts (mastitis). Retention of a placenta usually leads to metritis. Signs include continued straining as if in labor, vaginal discharge, fever, and depression. Drugs that help stimulate uterine contractions, such as oxytocin or prostaglandin F2alpha may help expel the placenta. Mastitis is usually caused by a bacterial infection and can be treated with appropriate antibiotics. Excessive bleeding from the vagina after delivery is rare and requires veterinary intervention when seen. However, small amounts of blood loss ("spotting") that lasts 12–16 weeks or more can be normal and does not usually require treatment unless excessive blood is lost.
Lack of milk production (agalactia) is uncommon in dogs, but can be associated with premature delivery of the litter. Dogs that do not produce enough milk should be examined by a veterinarian to check for other underlying diseases. The normal presence of colostrum (a clear, watery fluid produced before milk and containing important antibodies) should not be confused with agalactia. Contented puppies that gain weight daily after the first 24 hours are a good indication that milk production is adequate. If necessary, milk production can be stimulated by injections of oxytocin. If milk production is inadequate, puppies may need supplemental feeding.
Also see professional content regarding management of reproduction.