Abnormalities of Sexual Differentiation. Genetic errors that effect sexual development of an individual dog may occur during one of three time points following conception: 1) during chromosomal establishment of gender (chromosome monosomy [XO], trisomy [XXX or XXY], or chimerism [some cells XX, others XY in the same individual]; 2) when chromosomal gender is translated into gonadal gender (disagreement between actual chromosomal sex and reproductive organ sex such as when a bitches' ovaries are XY instead of XX); or 3) during actual development of the reproductive tract and organs (disagreement between actual chromosomal sex and reproductive organ development such as having an outward appearance of a bitch, but the internal organs of a male). When any of these situations occur, normal reproductive function is inhibited and there is a permanent and irreversible state of anestrus. Diagnosis of abnormal sexual differentiation can be confirmed by analyzing the chromosomes, a process known as karyotyping, from a blood or skin sample of the bitch.

Lymphocytic Oophoritis. This condition is an autoimmune mediated disorder that results in premature ovarian failure. The autoimmune disease may be isolated to the ovaries or occur in conjunction with a more wide-spread, systemic disease manifesting as skin lesions or polyarthritis. This disorder is diagnosed by surgical biopsy of the ovaries which reveals follicular degeneration and lymphocytic infiltration (suggestive of the immune-mediated reaction). Recommended treatment for this disorder is ovariohysterectomy since immunosuppression using corticosteroids to treat this disease has not been examined in terms of safety and efficacy in the dog.

Luteal Ovarian Cyst. Ovarian cysts are occasionally found in conjunction with occurrence of persistent anestrus. It is unknown if this finding is coincidental or if ovarian cysts play a contributory role in persistent anestrus. In any event, ovarian cysts should be suspected when progesterone levels exceed 2 ng/ml for more than the normal 2 month duration during a bitches' cycle. Symptoms of abnormal cycling combined with appearance of ovarian enlargement on ultrasound are indicative of an ovarian cyst but should be confirmed by biopsy. Ovarian cysts usually respond to treatment with prostaglandins; those that do not respond to drug therapy are treated by surgical excision.

Pituitary Insufficiency. Persistent anestrus occurs commonly in bitches with dwarfism resulting from hereditary abnormalities of the pituitary gland. Because pituitary function is critical for maintaining endocrine organ (thyroid, adrenal, ovary) functions, various endocrine abnormalities typically occur concurrently in bitches with this disorder. Additionally, the bitch will retain the size, haircoat and dentition of a puppy. Because there is a hereditary basis for this disorder, the recommended treatment for persistent anestrus resulting from pituitary insufficiency is ovariohysterectomy.

Ovarian Aplasia/Hypoplasia. Incomplete development and/or maturation of the ovaries will result in a state of persistent anestrus. Compromised anatomy of the ovaries and subsequent insufficient production of ovarian hormones result in an inability to regulate pituitary hormones. As such, chronic elevation of LH and FSH serum concentrations in the bitch is highly indicative of this disorder. This condition is irreversible and ovariohysterectomy is the usual course of action.

Brucellosis. Bacteria of the Brucella sp. are well known for inducing spontaneous abortion in the bitch. B. canis is the most common of the brucellosis-causing bacterial strains found in dogs and, as such, is routinely screened for by serological testing as part of the breeding management plan. Limitations to serological testing for B. canis, however, do exist and typically occur with use of the rapid slide agglutination test (RSAT) or the tube agglutination test which may result in false-positives or false-negatives. False-positives should be suspected if a dog is asymptomatic or concurrent blood cultures drawn at the same time as serological samples are negative for bacterial growth. Follow-up assessment with the agar-gel immunodiffusion (AGID) test will rule-out the possibility of false-positive results.

False-negatives will occur if serological testing is conducted within a 4 week period after the dog has initially contracted B.canis. Therefore, all negative tests should be confirmed by repeat testing 30 days from the first test before considering a dog to be free of infection.

B. canis infections in pregnant bitches will typically cause spontaneous abortions between 49 and 59 days after breeding, however, infections may also induce early spontaneous abortions with resorption of the fetuses, result in stillborn puppies, or cause death of puppies shortly after birth. A bitch that aborts a litter due to B. canis will demonstrate a brown or greenish-gray discharge that contains a large number of bacteria that will be infectious to both dogs and humans. Extreme caution, therefore, should be used when caring for a bitch suspected of harboring B.canis. At such point, collection of the vaginal discharge and specific culture testing for B.canis is usually sufficient to obtain the diagnosis.

Though B. canis is most often conceived as being transmitted from dog to dog during the actual act of copulation, the primary mode of transmission actually occurs via oronasal contact with infected body fluids. Therefore, spread of infection is not limited to breeding contact and as such, once introduced into a breeding kennel, the highly infectious B. canis will quickly spread through the population. Long-term, multiple treatments with antibiotics may assist in controlling symptoms and extent of infection within an individual dog, however, antibiotic treatment has limited efficacy for cure and the dog will remain potentially infectious to other dogs. As such, infected dogs should be neutered and removed from the breeding kennel environment to prevent spread to other breeding dogs. Retesting should be performed 6 months following completion of the antibiotic regimen to assess treatment efficacy. The alternative for controlling spread of B. canis is euthanasia of all confirmed-infected dogs.

Dogs may also become infected with other strains of Brucella sp. that typically infect livestock. Dogs with a history of spontaneous abortion, negative serological testing for B. canis, and exposure to livestock may harbor one of the other strains such as B. abortus, B. suis, and B. melitensis. Since serological tests for B. canis will not cross react with these other Brucella sp., dogs suspected of carrying an alternate strain of Brucella should be tested specifically for these other strains.

Canine Herpesvirus Infection. Canine herpesvirus infection occurs as a relatively mild viral infection in the average dog, however, new infection in a pregnant bitch or newborn puppies will usually result in spontaneous abortion or neonatal fatality. Greatest risk occurs in the last three weeks of pregnancy and the first 3 weeks of birth. The virus is commonly found in dogs, and as many as 80% to 100% of dogs with a history of high exposure to other dogs (such as show dogs and kennel dogs) will be found to have life-long, latent states of infection (asymptomatic infection). Bitches that become infected with herpesvirus during pregnancy will usually experience pregnancy complications resulting in fetal death, fetal mummification, spontaneous abortion, or premature birth. Newborns that become infected with the virus usually succumb to septicemia. Additionally, surviving puppies will typically show indications of permanent nerve, kidney and lymphatic system damage. Bitches previously infected with canine herpesvirus may have normal pregnancies and litters without fatality, but at other times have a spontaneous abortion or lose puppies following birth. Outcome in bitches harboring infection prior to breeding appears to rely on the maternal immune system status at the particular point in time.

Serological testing showing any degree of titer for canine herpesvirus infection is considered positive since humoral immunity to this virus is minimal and short-lived. Monitoring titer, however, may provide an indication of viral "flare-up" at a particular point in time and may be helpful for assessing immune status and potential pregnancy complications in those bitches that have previously lost litters to canine herpesvirus complications. Additionally, serological titer is useful for diagnosis of canine herpesvirus as a cause for spontaneous abortion in the pregnant bitch. When abortion occurs late in the pregnancy, histopathological examination of tissues from the aborted fetuses can be used to confirm the presence of canine herpesvirus infection.

Toxoplasmosis. The cat is the definitive host for the toxoplasmosis organism, however, dogs may serve as an intermediate host. As in humans, toxoplasmosis infection in the dog may produce spontaneous abortion, but more commonly causes developmental problems that will impact upon the puppies in life.

Dogs may become infected with toxoplasmosis by ingesting the organism when eating the feces of an infected cat, by eating infected meat, or in utero if the dam is acutely infected during the pregnancy (chronic infections in the dam are usually not transmitted to the fetuses). In the latter instance, if an infected litter survives, the puppies will usually develop symptoms of neurological, respiratory and gastrointestinal abnormalities.

Diagnosis of toxoplasmosis is accomplished by serological titers sampled 2 weeks apart. A significant increase in the second titer compared to the first titer is indicative of an acute toxoplasmosis infection. Chronic infections may present a high baseline titer (initial titer).

Prevention is the recommendation for reducing risk of toxoplasmosis infection in the pregnant bitch. Bitches should not be exposed to cat feces or raw meat, both of which may pose palatable temptations to the bitch. Since cats only shed toxoplasmosis during a brief time after exposure, chronically infected cats are not of particular concern.

Mycoplasma and Ureaplasma. These organisms are of the Mycoplasmataceae family and normally inhabit the canine urogenital and nasopharyngeal tracts. If, however, there is an increase in the number of these organisms in comparison to the other common organisms also inhabiting the vaginal tract of the bitch, then there is an increase in infertility, spontaneous abortion resulting in resorption or premature birth, stillbirth, weak puppies, or neonatal death. Bitches kept in large, overcrowded breeding kennels are at greatest risk for acquiring these infections.

Diagnosis of spontaneous abortion caused by Mycoplasma or Ureaplasma is obtained by vaginal cultures and cytological examination of the vaginal discharge for signs of inflammatory cells. Cultures may also be obtained from aborted fetuses for confirmatory results.

Administration of chloramphenicol or tetracyline is effective for Mycoplasma or Ureaplasma infections. These antibiotics, however, are not safe for pregnant bitches. Therefore, if a bitch is diagnosed with an infection during pregnancy, before complications occur, Erythromycin, which is less effective against the infection but safer to the developing fetuses is the recommended treatment.

Miscellaneous Bacterial Infections. The vaginal tract of the bitch houses a multitude of various organisms, anyone of which may become opportunistic pathogens under certain conditions. Some of these bacterial organisms that have been associated with spontaneous abortions or post-delivery complications most commonly include Escherichia coli and Streptococcus, or less commonly Salmonella or Campylobacter (particularly if diarrhea has been observed in the bitch or any humans in contact with her). Infections can occur in any bitch, however, endometrial hyperplasia that occurs with aging places older bitches at increased risk for these infections.

Bacterial infections of the uterus and urogenital tract during pregnancy usually present with clouded, sometimes green-tinged discharge and if left untreated often results in spontaneous abortion. When puppies survive they usually have neonatal conjunctivitis (infection of the eyes) and often die shortly after birth due to septicemia (systemic infection).

Culture and examination of the vaginal discharge will indicate bacterial infection and processes of inflammation, respectively (a special culture must be run separately if Campylobacter is suspected). Additionally, the bitch may have a fever. For treatment, the antibiotic administered will be based on efficacy as determined by sensitivity screening as well as safety to the developing fetuses if the bitch is still pregnant. When spontaneous abortions occur, care must be taken to ensure that the uterus is completely evacuated in order to control infection.

Miscellaneous Causes. Fetal genetic defects may result in resorption or stillbirth of effected fetuses, but generalized spontaneous abortion typically only occurs if all the fetuses are afflicted. Such defects are diagnosed by chromosome analysis of the fetal tissue.

Hypothyroidism has been linked to spontaneous abortion in bitches, however, its role in the occurrence of spontaneous abortion has not been established. In general, bitches with any type of endocrine disorder are discouraged from being bred because of the hereditary nature of many of these diseases.

Though nutritional deficiencies, particularly manganese deficiency, may lead to fetal demise, the widespread availability of nutritionally-balanced, commercial dog foods has made this a rare cause for spontaneous abortion. In regard to diet, however, the practice of calcium supplementation still has implications for producing pregnancy complications, such as uterine inertia and prolonged gestation, that may increase risk to both the fetuses and the dam.