A complete discussion of breeding and reproduction in dogs is beyond the scope of this book. 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 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.
During the proestrus stage, female dogs become attractive to males but still do not allow them to mate. A discharge from the vagina can be seen and the vulva starts to enlarge. Blood levels of the hormone estrogen rise during proestrus. In most dogs, proestrus lasts about 9 days.
During estrus female dogs are receptive to breeding by males. At this point estrogen levels are declining and progesterone levels increase. Estrus can be as short as 3 days or as long as 3 weeks, but is about 9 days long on average.
During the last phase, diestrus, female dogs again become resistant to breeding by males. Vaginal discharges diminish. The uterus enlarges due to stimulation by progesterone. Progesterone levels increase during the first half of diestrus, then slowly decline. Diestrus usually lasts for 2 to 3 months. If the dog becomes pregnant, progesterone levels stay high and the pregnancy lasts for about 65 days.
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 and changes in the skin and liver. 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 the hormone prostaglandin F2alpha or the corticosteroid dexamethasone.
Pregnancy and Delivery
Pregnancy in dogs can be detected by physical examination (palpation of the uterus) at about day 30 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. This is also 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 65 days in dogs, but predicting the timing of delivery can be difficult. 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. During Stage II, abdominal contractions can be seen and the puppies are delivered. The puppies are usually delivered at intervals of 1 to 2 hours, but that can vary considerably. Stage II can last up to 24 hours. Stage III is defined as the delivery of the placenta. Dogs typically alternate between stages II and III until delivery is complete.
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 or II or more than 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 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. 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 Routine Care and Breeding of Dogs: Puppy Care).
Problems Associated with Delivery
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 (see Metabolic Disorders of Dogs: Disorders of Calcium Metabolism in Dogs). 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 (see Reproductive Disorders of Dogs: 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 (see Reproductive Disorders of Dogs: Mastitis) is usually caused by a bacterial infection and can be treated with appropriate antibiotics.
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.
Last full review/revision July 2011 by Cheri A. Johnson, DVM, MS, DACVIM (Small Animal); Brad E. Seguin, DVM, MS, PhD DACT; Autumn P. Davidson, DVM, MS, DACVIM; Fabio Del Piero, DVM, DACVP, PhD; James A. Flanders, DVM, DACVS; Mushtaq A. Memon, BVSc, MS, PhD, DACT; Paul Nicoletti, DVM, MS; Robert C. Rosenthal, DVM, PhD, DACVIM (Small Animal, Oncology), DACVR (Radiation Oncology)