If a dog successfully conceives, what can cause pregnancy loss?
Pregnancy loss may be attributed to several factors. Imbalances in reproductive hormones may result in insufficient hormone levels to sustain a pregnancy. Other hormonal imbalances (e.g., diabetes and hypothyroidism) may affect reproductive hormone levels and result in pregnancy loss. The administration of certain drugs (e.g., corticosteroids) may lead to fetal death, as can some infections (e.g., Brucellosis).
Some of the basis for the diagnosis will be related to whether your dog has conceived or given birth in the past. If she has reproduced successfully before, your veterinarian will consider whether the male mate that has been chosen for breeding is of proven fertility, or whether the timing for the breeding was scheduled in accordance with your dogs ovulation cycle.
A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. These tests will show evidence of infections, either bacterial, viral, or parasitic. Viral infections that will be tested for include toxoplasmosis, protozoal parasite infection, canine herpesvirus, hypercorticolism, hypothyroidism, and Brucella canis. In addition, your doctor will be checking your dogs body thoroughly for any other chronic disease conditions.
Infertility can affect dogs of all ages, but tends to be more common among older dogs. An underlying cystic endometrial hyperplasia — uterine cysts — is more common among dogs past the age of six. Dogs that have had previous uterine infections can also have subsequent difficulties with implantation. However, one of the most causes of seeming infertility is insemination during the improper time in the estrous cycle.
Imaging techniques may be used to look for any abnormalities in the uterus, such as masses (indicating tumors), and anatomic abnormalities that would interfere with conception. In a healthy dog, the ovaries and uterus will not be visible on X-ray imaging. If your veterinarian is able to view the ovaries or uterus, this would suggest that there may be an underlying condition of ovarian cysts, ovarian cancer, or uterine cysts. If it appears, on examination, that your dog has cysts or other masses of tissue in the uterus or reproductive tract, your veterinarian will need to take a sample of tissue from the uterus for biopsy.
Some of the common symptoms that appear in bitches which are unable to reproduce are abnormal cycling, failure to conceive, failure to copulate/mate, and pregnancy loss. Normal fertility in a dog, and the ability to reproduce puppies, requires a normal estrous cycle, with a healthy reproductive tract, normal ova (eggs), normal and stable levels of reproductive hormones, fertilization by normal spermatozoa, implantation of an embryo in the lining of the uterus (endometrium), normal placenta placement, and stable levels of progesterone concentration. These conditions must be maintained for the entirety of the two month gestational period, or the process of reproduction will be altered, with resultant infertility.
What are the causes of infertility in female dogs?
Fertility problems in female dogs can be broken down into broad categories: abnormal estrous cycling, failure to copulate (breed), failure to conceive, and pregnancy loss.
Abnormal estrous cycling is a term used to describe a female dog that is not experiencing normal heat cycles. These abnormalities may include delayed, absent, or irregular cycles. A normal female dog should begin having estrous (heat) cycles by two years of age.
There are several stages in the estrous cycle; the stage called estrus refers to when the female is in heat or is sexually receptive. Once these cycles begin, the dog should experience estrus at regular intervals. Most female dogs cycle every four to ten months, although some dogs may only cycle once per year.
Primary persistent anestrus describes a female dog that has reached two years of age without estrous cycling. This condition may be caused by several factors including malnutrition, excessive physical activity, medications that interfere with fertility, or a lack of exposure to other cycling females.
If a dog has experienced one cycle but does not cycle again, secondary persistent anestrus may be diagnosed. This term describes a delay of over 18 months since the last estrus. In some dogs, this is an age-related condition; dogs under two years of age may experience irregular cycles and the same is typically seen in older dogs.
A variety of infections (e.g., E. coli, brucellosis, ureaplasmosis) and metabolic diseases (e.g., renal failure, hypothyroidism, Cushing’s disease) may cause systemic diseases that can lead to a failure to cycle. Exposure to oral and topical steroids (such as those used by humans), hormonal imbalances, and ovarian tumors may also lead to persistent anestrus.
A dog that remains in heat for over six weeks is diagnosed with persistent estrus. Causes of persistent estrus include exposure to exogenous hormones (intentionally or unintentionally), hormonally active ovarian cysts, and ovarian tumors.
Irregular estrus cycling indicates that the ovaries are not functioning properly. In this case, abnormal hormone levels are often responsible for a failure to trigger regular estrous cycles.
Additionally, hormonal imbalances and genetic disorders may prevent normal estrous cycles. Some dogs experience a condition called silent heat, in which they do ovulate but the characteristic signs of being in heat, such as vulvar swelling and discharge, are not observed. Although rare, some dogs may also have an autoimmune disease that affects their ovaries and interferes with estrous cycling.
If the time of fertility is inaccurately estimated, this may lead to the female being unwilling to copulate. Many cases of female infertility are likely related to poorly timed breeding.
Behavioral factors may contribute to a refusal to copulate. These factors include a dominant female dog refusing to stand for a submissive male, attempts to breed a female that is sexually immature, a stressful or otherwise unpleasant breeding environment, and inappropriate behaviors by either the male or female.
Physical factors may contribute to a failure to copulate if they are a source of pain for the female. Common physical factors include hereditary abnormalities of the vagina, a history of vaginal trauma, or vaginal growths. Additionally, conditions such as osteoarthritis or back pain may make females resistant to standing for a male.