THIRTY-SEVEN: Abortion, Abnormal Estrous Cycle, and Infertility


Problem Definition and Recognition

Abortion can be spontaneous or induced. In this chapter all discussion will be confined to spontaneous abortion in the bitch and queen. Spontaneous abortion refers to a clinical condition describing the loss of a fetus/conceptus prior to its ability to survive in an extrauterine environment. The exact frequency of spontaneous abortion in the general population is unknown. However, with the increasing use of ultrasonography in early pregnancy diagnosis, better information is being gathered. In all domestic species it is estimated that more pregnancies are lost spontaneously than are actually carried to term.

The exact incidence of embryonic and fetal loss is difficult to determine. If fetal death occurs during the first half of pregnancy, an unobserved abortion or resorption often occurs. Because external signs of pregnancy and/or pregnancy loss often are undetectable at this stage, both veterinarians and bitch owners may be uncertain if a pregnancy was ever established and if so how many embryos originally entered the uterus. There have been several studies suggesting approximately a 10% early embryonic loss rate.

If fetal death occurs during the second half of pregnancy, abortion or birth of stillborn pups occurs. Often abortion is accompanied with a serosanguineous to uteroverdin vulvovaginal discharge and the passage of fetal tissues. If a fetus dies in late gestation and is not aborted, fetal emphysema and maceration often result. Bitches that retain macerated fetuses frequently have a foul and fetid uterine discharge and may become systemically ill, showing signs of toxemia or septicemia. However, overt clinical signs may be absent or go unnoticed in bitches who abort and bitches may consume or hide the aborted fetuses making diagnosis more difficult.


Abortion may occur at any stage of gestation and may be manifested by embryonic death, abortion of a live or dead fetus, stillbirths, or fetal death with expulsion or mummification and retention within the uterus (or rarely, peritoneal cavity) beyond normal gestational length. Whether the fetus is “resorbed”/sloughed unnoticed, aborted, a full-term stillbirth, or retained as mummified tissue depends on the etiology, stage of gestation at which death occurs, and other varied maternal and fetal factors.

Fetal death occurring in late gestation, not associated with abortion or maceration, may be followed by fetal mummification. Fetal mummification does not occur during the first half of pregnancy because embryonic or fetal death prior to the development of fetal bones usually is followed by unobserved discharge or tissue resorption.

Causes of Abortion

Canine. The causes of embryonic loss/fetal death in the bitch are both noninfectious and infectious. Infectious causes of embryonic and fetal loss include viral, bacterial, protozoal, and possibly mycoplasma infections. See Table 37-1 for the causes of canine abortion.

Viral causes in the bitch include canine herpes virus, canine parvovirus types 1 and 2, and canine distemper virus.

Bacterial causes in dogs include Brucella canis and other Brucella species, Campylobacter, Salmonella, Escherichia coli, Streptococcus species, and other bacteria. B. canis infections may cause embryonic death, abortions, testicular atrophy, epididymitis, scrotal dermatitis, infertility, and generalized lymphadenitis in both sexes. Canine brucellosis has been diagnosed in many breeds throughout the United States, as well as in several other countries.

Protozoal causes of abortion may include Neospora caninum. This organism has been associated with abortion in cattle for several years and has been studied experimentally in the bitch. Whether N. caninum is a significant cause of naturally occurring canine abortion is unknown, in that they are a known natural reservoir for this organism. Toxoplasma gondii has been reported to infect pups in utero resulting in neonatal death.

Under noninfectious causes of embryonic or fetal death, hypoluteoidism has been suggested. The maintenance of canine pregnancy is dependent on serum progesterone concentrations greater than or equal to 2 ng/mL. Therefore, abortion often results when concentrations of progesterone drop lower than this for greater than 24–48 hours. Hypo-luteoidism may be a factor in pregnancy loss if infectious and other causes for fetal death are absent.

TABLE 37-1. Causes of abortion in the bitch

Infectious Noninfectious
  1. Canine herpes virus   1. Hypoluteoidism
  2. Canine parvovirus types 1 and 2   2. Exogenous drugs
  3. Canine distemper virus   3. Trauma
  1. Brucella canis  
  2. Other Brucella sp.  
  3. Campylobacter  
  4. Salmonella   
  5. Escherichia coli   
  6. Streptococcus sp.   
Mycoplasma and Ureaplasma   
  1. Neospora caninum   
  2. Toxoplasma gondii   

TABLE 37-2. Causes of abortion in the queen

Infectious Noninfectious
Viral   1. Nutritional deficiencies
  1. Feline herpesvirus   2. Genetic abnormalities
  2. Feline immunodeficiency virus   3. Exogenous drugs
  3. Feline infectious peritonitis virus   4. Environmental factors
  4. Feline panleukopenia virus  
  1. Brucella sp.  
  2. Salmonella sp.  
  3. Escherichia coli  
  4. Streptococcus sp.  
  5. Staphylococcus sp.  
  1. Toxoplasma gondii  

Hypothyroidism has occasionally been linked to infertility due to the role of iodine in proper thyroid gland function and reproduction in many species; however, available information fails to correlate hypothyroidism with infertility or pregnancy loss in the bitch.

Exogenous drugs, as well as, genetic, immunologic and environmental factors, and trauma must also be considered as potential causes of pregnancy loss.

Feline. In the queen infectious causes of spontaneous pregnancy loss may be associated with viruses, bacteria, and protozoa (see Table 37-2). Infection with T. gondii has also been associated with feline abortion due to debilitating systemic illness and not due to uterine, placental, or fetal lesions. See Table 37-2 for a list of infectious and noninfectious causes of feline abortion.

Diagnostic Plan—Canine Abortion

Transcutaneous abdominal ultrasonography is a reliable and sensitive method to ascertain pregnancy diagnosis, fetal viability and/or fetal demise in both the bitch and the queen. It is a tremendous aid in the diagnosis of abortion or pending abortion as early as 24 days of gestation. It allows the determination of viability of one or multiple fetuses and/or their death. Abdominal radiography can also be used later in gestation to detect collapse or decalcification of bones, the development of intrafetal gas, or an abnormal fetal position.

The post abortion diagnostic plan in the bitch and queen is outlined in Table 37-3.

A proper diagnosis begins with a thorough history with complete breeding records, including previous problems associated with the reproductive tract, and a complete physical examination. Results of prebreeding Brucella testing of the bitch and stud dog, as well as previous breeding mates, are critical. Additional information should include recent travel, potential contact and/or exposure to outside animals, vaccination and deworming protocols, housing, and exposure to other medications and potential toxins. The physical examination of the bitch should include a digital and visual vaginal examination, a complete blood count, vaginal cytology, and urinalysis. Hormone assays for progesterone and relaxin may be of some value.

TABLE 37-3. Diagnostic plan for abortion

  1. History with complete breeding records
  2. Complete physical examination including digital and visual vaginal examination
  3. Results of prebreeding Brucella canis testing of the bitch and stud dog
  4. Complete blood count
  5. Vaginal cytology
  6. Urinalysis
  7. Hormone assays for progesterone and relaxin (±)
  8. Postabortion Brucella canis titer
  9. Aborted fetus
    a. Necropsy
    b. Bacterial culture
    c. Histopathology
    d. Karyotyping
  1. History with complete breeding records
  2. Complete physical examination including digital and visual
  3. Complete blood count
  4. Vaginal cytology
  5. Urinalysis
  6. Feline leukemia test
  7. Aborted fetus
    a. Necropsy
    b. Bacterial culture
    c. Histopathology
    d. Karyotyping

A postabortion B. canis titer should be determined. Several serologic tests are available for presumptive, but not definitive, diagnosis of canine brucellosis. A blood culture at the early stage of infection (5–6 weeks) should be positive; however, a negative culture postabortion does not rule out the disease.

If a freshly aborted fetus is available, necropsy with histopathologic study of major body tissues and culture of stomach contents for bacteria should be performed. All aborted material and discharges from the vagina should be handled carefully (wearing gloves), since B. canis is infectious to humans. Bacterial and/or viral cultures of fetal and placental tissues are important, but can be confusing in the face of contamination and autolysis.

Finally, the abortus can be karyotyped if no maternal causes for abortion are evident. It should be remembered that a specific cause of abortion is often not found, even when all samples are collected and submitted correctly.

Preassembled kits for necropsy and abortion samples are available through several diagnostic laboratories. We recommend contacting your regular diagnostic laboratory to obtain a kit or specific instructions to increase the odds of obtaining a correct diagnosis.

In the postabortion bitch, if a bacterial infection is suggested by vaginal cytology or urinalysis, bacterial cultures should be performed on urine collected by cystocentesis and on discharge collected from the anterior vagina using a guarded culture swab. If the initial diagnostic tests are negative or normal, paired titers for toxoplasmosis are indicated. If abortion has previously occurred with no apparent cause, serumprogesterone concentrations should be monitored during the next pregnancy.

Diagnostic Plan—Feline Abortion

The diagnostic plan for the queen is similar to the one described for the bitch (see Table 37-3). In addition to the tests listed for the bitch, a complete blood count and feline leukemia virus test are always indicated. Vaginal and urine (cystocentesis sample) cultures are indicated when uterine infection is suspected. As with the bitch, if the queen has a history of repeated abortion of unknown cause, serum progesterone concentrations should be monitored during the next pregnancy.

Abnormal Estrous Cycles and Infertility in the Bitch

Problem Definition and Recognition

As described by Feldman and Nelson (see “Suggested Readings”):

Infertility or apparent infertility problems in the bitch are common. Veterinary advice is often sought after a bitch fails to conceive, if she fails to exhibit “normal” breeding behavior, when her cycles appear to be unusual, or for myriad other disturbances. “Infertility” therefore, is a huge category comprising a long list of anatomic, physiologic, and behavioral problems, as well as, a number of apparent husbandry misunderstandings.

Fertility in the bitch requires a normal healthy reproductive tract, the ovulation and proper maturation of normal oocytes, insemination of normal sperm at the appropriate time, and maintenance of pregnancy for a normal gestation of approximately 63 days. The basic reproductive data for the bitch are listed in Table 37-4.

The marked variation in age of onset of estrous is in part due to the variety of breed sizes, with smaller breeds cycling earlier and larger breeds later. The first and second cycles may be irregular, unusual, short, or long; therefore, infertility evaluations are delayed in most dogs until they are 24–30 months of age. Also, as a general rule, almost all breeds cycle once every 4.5–10 months except some African breeds cycle only annually.

Estrous cycle abnormalities associated with infertility may include the absence of estrous cycles in bitches 2–8 years of age, prolonged standing estrus, short, split, false, or silent estrus, prolonged proestral bleeding, and very short or very long interestrous intervals. Infertility can also occur in bitches with normal-appearing estrous cycles.

TABLE 37-4. Normal reproductive data for the bitch

  Associated with the first heat cycle, normally between 3.5 and 24 months of age
  The average age at first heat (estrus) is 10–12 months and generally earlier among smaller
  breeds and later among larger breeds
  Breeding not recommended on first heat
Seasonality of ovarian cycle
  Ovulation can occur at any time of the year
  Winter and spring months appear to be overrepresented
  This may be genetic or management based
Interval between cycles
  7 months with a normal range of 5–12 months for all breeds except the basenji, which is 1 year.
Phases of cycle
  Proestrus: Heightened ovarian (follicular) activity—9 days average (range 0–27 days)
  Estrus: Allows male to mount and will stand for breeding—5–9 days (range 4–24 days)
  Diestrus: Period of corpus luteal activity (56–58 days if pregnant; 60–100 days if nonpregnant)
  Anestrus: quiescence ∼4.5 months


The causes of infertility can be subdivided into three categories: infertility with (1) a normal estrous cycle (behavioral), (2) an abnormal estrous cycle but a normal interestrous interval, and (3) an abnormal estrous cycle with an abnormal interestrous interval. The causes of infertility in the bitch are listed in Table 37-5.

Normal Estrus Cycle. Improper breeding management is the single most common cause of infertility in the bitch. Conception failure caused by mistimed breedings approaches 50% of infertile bitches. Ovulation may occur only 3–4 days or as late as 26 days after the onset of proestrus. Breeding by the day of cycle alone has been reported to produce pregnancies well below 80%. Pregnancy rate can be significantly improved if day of ovulation is determined by vaginal cytology and hormone concentration assessment. Conception rate is best in bitches bred from 3 days before to 4 days after ovulation, with maximal litter size if bred 2 days after ovulation in the “normal” estrus cycle.

Male infertility is the next most common cause of conception failure in bitches. Male infertility is discussed in subsequent sections.

TABLE 37-5. Causes of infertility in the bitch

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May 25, 2017 | Posted by in SMALL ANIMAL | Comments Off on THIRTY-SEVEN: Abortion, Abnormal Estrous Cycle, and Infertility
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A. Infertility with normal estrus cycles
  1. Improper breeding management
  2. Male infertility
  3. Uterine disease and pathology