Several unique features of the canine estrous cycle, together with dog sperm longevity, allow for dog's high conception rate after a single mating. Many bitches, however, are seemingly infertile; that is, they fail to conceive or whelp a normal litter. Determining the cause of apparent infertility requires a logical diagnostic plan. Because of the relatively long interval between estrous cycles in the bitch, dog owners are encouraged to seek veterinary consultation after a bitch's first reproductive failure. Failure to do so may lead to a false assessment, misguided treatment, and possible harm to a potential breeding bitch. The approach to infertility in the bitch described here is used in the clinical practices of the authors and is presented as a guide for dog owners and veterinarians to use together.


A brief review of the canine estrous cycle, including reproductive hormone patterns and vaginal cytology, follows to provide the necessary background for understanding the rationale of the diagnostic approach discussed in this article.


The initial evaluation of an apparently infertile bitch includes collecting a general medical history and complete physical examination. The approach to infertility outlined here is designed for treating bitches that have no apparent systemic disease. Also, the current and previous use of any medication, especially corticosteroids for flea-allergic dermatitis, must be known in making an accurate evaluation. Routine laboratory testing (e.g., complete blood count, serum biochemical profile, and urinalysis) may be indicated on the basis of the animal's history and physical examination.

The possibility of Brucella canis infection must be considered in any bitch presented for infertility, and all dogs should be screened for antibody to B. canis on a routine basis before breeding.

It is also prudent to rule out infertility in the male used for breeding before investigating a bitch for apparent infertility. This is commonly done on the basis of the male's history (e.g., Was the dog siring litters at the time the bitch in question was bred?). Semen evaluation may be necessary to determine the viability of sperm if there is no historical evidence of male fertility.


The apparently infertile bitch can be classified on the basis of prior oestrous-cycle characteristics as follows:

  • normal oestrous cycle length and normal estrous cycle events

  • failure to cycle

  • prolonged interestrous intervals (>10 months); 

  • shortened interestrous intervals (<4 months)

  • persistent estrus 

1) Normal Oestrous Cycles

Bitches with normal Oestrous cycles are the most common group to present for failure to conceive or whelp a litter. The potential differential diagnosis can be investigated by answering the following questions.

Does normal mating occur? If a bitch will not accept the male for breeding, it is important to determine if the bitch is in estrus. common management practices may dictate that bitches be bred on predetermined days of the cycle such as days 11 and 13 (the first day of proestrus is considered day 1). A bitch may not be in estrus on these days, however, if her proestrus or oestrus deviates from the average duration. The use of daily vaginal cytology and observations of the bitch's behavior in the presence of a male dog (a teaser) are the most accurate means for determining the onset of behavioral oestrus.

If the bitch appears to be in oestrus but refuses breeding, it is possible that a vaginal or vulvar anatomical obstruction prevents intromission or causes painful breeding. Careful digital vaginal palpation and vaginoscopic examination by the veterinarian are indicated. Contrast radiographic procedures may be necessary to outline anatomical abnormalities, including vaginal masses; and surgery may be necessary for resolution of the problem.

Other possible causes of a bitch's refusal to be bred include the use of an inexperienced male, behavioral problems (of the bitch or the male), and mate preferences. the female should be taken to the male's environment so that he can dominate the breeding event. some bitches that are transported early in estrus, however, may abruptly terminate estrus behavior as a result of stress or tranquilization. in such cases, transportation in advance of an expected proestrus, or the use of transported semen, may be necessary.

Does mating occur during the bitch's fertile period? The bitch may display estrus behavior for longer than the duration of the time in which she is capable of conceiving. the fertile period can be estimated retrospectively from vaginal cytology by counting back five to six days from the onset of cytologic diestrus. again, a bitch that is routinely bred on predetermined breeding dates may be bred at a time she is not fertile. this problem most commonly occurs in bitches that are bred early in estrus. because dog sperm is viable in the female genital tract for four to 11 days, however, conception can occur even if the bitch is bred at a non-fertile time. to optimize the possibility of conception in bitches that have failed to conceive in the past, we recommend a management program as follows: 

the owner should obtain daily swabs for vaginal cytology beginning on day 1 of proestrus and continuing throughout estrus. 
to determine accurately the onset of oestrus, the bitch should be "teased" with a male dog every one to two days beginning when the vaginal cytology shows signs of late proestrus/early oestrus. 
once in oestrus, the bitch should be bred every two to four days throughout the duration of oestrus regardless of the number of matings that occur. 
the owner should observe the breedings to be able to report whether they were normal (ie: whether there was a normal "tie"). 
pregnancy should be assessed by ultrasonography 16 to 21 days after breeding. 
The vaginal cytology obtained by this protocol will allow the veterinarian to: 

determine when the bitch is likely to be in estrus which should be substantiated by response to the teaser male 
determine retrospectively on the basis of the first day of diestrus, the likely fertile period of the bitch. if the bitch was bred during this fertile period, is not pregnant, and the male has been shown to be fertile, then the bitch should be further investigated for infertility. 
Does the bitch ovulate? A bitch that is determined not to be pregnant by ultrasonography 21 to 28 days after oestrus should be evaluated to determine if ovulation occurred. Serum progesterone concentration at that time in the cycle should be in excess of 5 ng/ml. concentrations between 2 and 5 ng/ml may indicate the bitch has ovulated but is unable to maintain a corpus luteum (hypoluteoidism, to be discussed later). If the progesterone concentration is <2 ng/ ml, it is likely the bitch did not ovulate and should be observed for the occurrence of a "split heat." Split heat is defined clinically as the situation of a bitch that goes into estrus, does not ovulate, and is again in estrus within two to four weeks; it is most common in pubertal bitches. Often, ovulation will occur after the second estrus. Ovarian cysts can cause ovulation failure and may be detected by ultrasonography. If ovulation failure without apparent cause has been documented, the bitch may be induced to ovulate at the next cycle by injections of human chorionic gonadotropin. Signs of false pregnancy (a response to a decrease in progesterone levels) at the end of diestrus can serve as an indirect and inexpensive indication that ovulation did occur.

Does the bitch have a normal uterus? When it appears that the bitch's ovarian function is normal (i.e., she has normal estrous cycles and ovulates), it must be determined whether the uterus is capable of maintaining pregnancy. Ultrasonography is a non-invasive method that can be used to evaluate the uterus. In the healthy non-pregnant bitch, during any phase of the oestrous cycle other than estrus the uterus is sonographically small and free of luminal fluid and is commonly not detected at all. An enlarged or fluid-filled uterus may be an indication of chronic pyometritis or cystic endometrial hyperplasia. Pyometra can be medically managed with prostaglandin therapy. Cystic endometrial hyperplasia is most common in older bitches or in those previously treated with progestational agents, is diagnosed by uterine biopsy obtained at abdominal surgery, and is not reversible.

Vaginal cultures are often obtained in an effort to determine whether a bacterial infection may be the cause of infertility. The theory behind this practice is that bacteria present in the cranial vagina may indicate bacteria in the normally sterile uterus; the problem with this hypothesis, however, is that bacteria of many types have been isolated from the cranial vagina, and hence it cannot be considered a normally sterile environment. A positive culture from the cranial vagina does not necessarily reflect the presence of bacteria in the uterus. the only way to determine accurately whether there are bacteria within the uterus is by uterine biopsy and culture of uterine tissue. bacterial cultures of the caudal vagina are commonly positive and are indicative of the normal bacteria that inhabit that area. Overall, vaginal cultures are of little use in the infertility evaluation unless vaginitis is present. vaginitis is treated by antiseptic douching.

Does the bitch resorb or abort fetus'? A bitch that become pregnant then loses the litter before day 30 of gestation will most likely resorb the fetus', whereas if the litter is lost later in gestation, the fetus' will likely be aborted. Potential causes of such a problem include fetal development abnormalities, uterine or systemic disease of the bitch (including b. canis or canine herpes virus infection), drug administration and hypoluteoidism. Resorption or abortion may be suspected in the bitch that is diagnosed pregnant by abdominal palpation (at approximately day 28 of gestation), and does not whelp a litter. to determine accurately that a bitch is pregnant early in gestation, ultrasonography should be performed after day 16 to 21 of gestation. Routine abdominal radiography can be used to diagnose pregnancy only after fetal bone calcification-after approximately day 44 of gestation. when a resorption problem is suspected, the bitch should be sequentially monitored by ultrasonography during the next pregnancy and should have a concurrent serum progesterone analysis to determine if hypoluteoidism occurs. If the progesterone concentration falls below 2 ng/ ml, the bitch will likely resorb or abort the fetus', depending on the stage of gestation; therapy in such cases involves supplementation with progesterone until day 50. Inappropriately treating a bitch that does not require such therapy, however, can lead to abnormal development of the fetus' (e.g., masculinization of the females) and potential problems with parturition.

2) Failure to Cycle:

Potential differential diagnoses for a bitch that apparently fails to cycle may be investigated by answering the following questions.

Has the bitch ever had an oestrous cycle? The age of the bitch that has never displayed signs of an oestrous cycle (primary anestrus) must first be determined. A bitch is not routinely evaluated for primary anestrus until she is beyond two to three years of age, although bitches of many breeds (especially of smaller stature) normally experience a first oestrus (pubertal oestrus) at a younger age. A bitch with primary anestrus should be evaluated for signs of an intersex condition. The female genitalia may appear normal, but the bitch may have abnormal internal reproductive organs and hence will not cycle. Chromosome analysis may be performed with a blood sample.

Bitches may have a silent heat, i.e., they may ovulate but show minimal to no signs of proestrus or oestrus. This can be determined by monthly evaluation of serum progesterone concentration to determine whether the bitch recently ovulated. Weekly determination of vaginal cytology may alert the owner to the onset of the next proestrus and estrus even though signs may not be observed, such bitches may be fertile but require artificial insemination. Future cycles may be associated with normal clinical signs.

Has the bitch had estrous cycles in the past and now fails to cycle? This problem can occur in a bitch that has concurrent systemic disease, such as an endocrine disorder, a generalized infectious process, or cancer. Common endocrine diseases include hypothyroidism and hyperadrenocorticism (cushing's disease). Laboratory tests are necessary to diagnose definitively such disorders, and with proper treatment the bitch may become fertile. Another consideration is that the use of some medications may suppress the hormonal events necessary for ovarian function. Corticosteroids, frequently administered in the treatment of skin allergies, may be the cause of secondary anestrus.

The functional longevity of the ovaries in the bitch is unknown. although ovarian function generally declines after the bitch is eight to 10 years old, the ovaries may cease to function earlier (premature ovarian failure). Pituitary hormone serum concentrations reflect ovarian function because when the ovaries fail, the pituitary gonadotropins (follicle stimulating hormone [fsh] and lh) continue to be produced and reach high serum concentrations. Currently, few centers in the united states have the facilities for determining fsh and lh concentrations. Premature ovarian failure is not a treatable condition. This diagnostic approach also can be used to determine if a bitch with an unknown past history has been ovariohysterectomized.

3) Prolonged Interestrous Intervals :

Interestrous intervals greater than 10 months are considered prolonged in dogs, with the exception of the Basenji. In aging females (those older than eight years) the interestrous interval may lengthen. If such prolonged cycles are fertile, an investigation into the cause of the long interval is not indicated. Possible differential diagnoses for infertile cycles that have a prolonged interestrous interval may be explored by answering the following questions.

Does the bitch have undetected cycles? A bitch that has a prolonged interestrous interval should be evaluated to determine if a silent heat is occurring between observed estrus periods. This may be determined as discussed above. housing the bitch with another female may induce an earlier cycle.

Does the bitch have an underlying disease process? The bitch should be evaluated for underlying disease that can delay the onset of an estrous cycle. hypothyroidism, in addition to causing persistent anestrus, can cause a prolonged interestrous interval. diagnostic testing, including a response of thyroid hormone (t4) concentration to an injection of exogenous thyrotropin (tsh), is indicated. when hypothyroidism is the cause of the prolonged interestrous intervals, other concurrent signs of hypothyroidism, including dermatologic abnormalities, inappetence, and lack of energy, are usually apparent.

In bitches with persistent anestrus or prolonged interestrous intervals, an attempt can be made to induce estrus hormonally. At the university of California - Davis, studies are currently under way to evaluate the administration of gonadotropin-releasing hormone (gnrh) to induce oestrus and ovulation in bitches. Endogenous gnrh is released from the hypothalamus and causes the pituitary to release fsh and lh. Administering gnrh therefore simulates normal physiologic events of the estrous cycle.

4) Shortened Interestrous Interval:

Cycles that recur every four months or more frequently are considered abnormal. 

Possible differential diagnoses for this problem can be investigated by answering the following questions.

Does the bitch ovulate? Determining the serum progesterone concentration will indicate whether frequent oestrus periods are associated with ovulations. If they are not, the bitch may be having a split heat. When she does ovulate, she should be fertile. Split heat is most frequently associated with young or pubertal bitches; it is therefore advisable to wait until the bitch is two to three years old before intervening.

Does the uterus have time to involute? In bitches that cycle every four months or less and ovulate, the uterus may not have time to recover from the previous cycle. A uterine environment that cannot support a pregnancy may develop. In such cases, one approach to management is to suppress estrus with mibolerone (cheque drops - Upjohn), an androgenic compound, administered orally for six months. Suppression of estrus will allow the uterus to involute completely. The bitch should be bred when estrus recurs after withdrawal of the drug.

5) Prolonged / Persistent Oestrus:

Oestrus is considered prolonged in a bitch that has behavioral signs of oestrus for longer than 21 days. Possible causes include an estrogen-secreting ovarian tumor or cyst. Abdominal ultrasonography can be used to observe ovarian structures. A negative scan does not rule out such a problem, however, and exploratory surgery may be necessary to visualize the ovaries. Another possible explanation in cases of apparently prolonged estrus is that the bitch may have vaginitis, in which case she may attract males, and this may be mistaken for a sign of oestrus. Vaginitis can be differentiated from oestrus by vaginal cytology.

A Clinical Approach to Infertility in the Bitch 
by J.L. Cain and E.C. Feldman

Canine Pregnancy Failure

Determining the cause of pregnancy loss in the dog can be frustrating. Despite a thorough investigation, identifying a specific cause of abortion is not always possible. It is very important to obtain proper tissue and blood samples for submission to Antech laboratories when attempting to find the reason for abortion, premature delivery, still-birth or the birth of weak neonates. 

The maintenance of pregnancy depends on many biological interactions between the pregnant female and the embryo or fetus. Before implantation, the fluid environment within the uterine tubes and the uterus supports early embryonic development. If this environment is inhospitable, embryos may not survive. Embryonic deaths that occur before or during implantation are not recognized because the embryos are lost before pregnancy can be diagnosed. Specific causes of early embryonic death are difficult to identify. 

Aged gametes, chromosomal and developmental defects have been associated with an increased incidence of early miscarriage in women. In bitches, these could result in early embryonic death and infertility. After implantation, the conceptus depends almost entirely on the dam. The conceptus will not survive if the dam is unable to adjust to the physical requirements and demands of pregnancy. Hypothyroidism, hypoluteoidism, nutritional deficiencies, uterine abnormalities, and exposure to some medications or infectious agents during pregnancy may contribute to impaired placental function, resulting in abortion. A list of chemical agents that may be harmful during pregnancy has been published in Kirk's Current Veterinary Therapy X, W B Saunders, pp 1291-1299, 1989. 

Abortion is defined as the expulsion, before full term, of a conceptus incapable of independent life. Clinical signs of abortion in the bitch include vaginal discharge and abdominal contractions with expulsion of live or dead fetuses. Vaginal discharge associated with abortion should be differentiated from that occurring with conditions such as vaginal masses or foreign bodies, endometritis, and open-cervix pyometra. Signs of septicemia may also be present in some cases of abortion. 

A thorough reproductive background including the breeding dates for the current and previous pregnancies; litter data for the sire or sires used; previous whelping dates, and the results of previous pregnancies (e.g. the number of puppies and whether live or stillborn, assisted or unassisted delivery, abortion), as well as the vaccination history; results of previous Brucella canis serologic testing; and information about the animal's housing and diet are important for determining potential causes of pregnancy losses. The physical examination will indicate the general health and nutritional status of the bitch as well as the possibility of any concurrent disease process. Potential infectious causes of abortion are included in Table 1

Recommended laboratory diagnostic tests include a CBC, serum chemistry profile, comprehensive thyroid hormone profile, urinalysis, and serologic tests for B. canis, Toxoplasma gondii, and canine herpes virus. Any canine herpes virus titer present at the time of abortion is of diagnostic significance because the antibody response is short-lived. Also, antibody titers for B. canis may be undetectable until as late as 4-8 week postinfection, and so titers may not be elevated at the time of abortion. Interpretation of titer results is difficult and should be done with the assistance of a clinical pathologist. 

To identify the presence of inflammatory cells and bacterial infection, collect samples from the anterior vagina or from vaginal discharge for cytologic examination and culture. Because a variety of organisms can be isolated in healthy animals (e.g. Escherichia coli, staphylococci and streptococci), cytology results and clinical signs must be considered when interpreting vaginal culture results. Place samples to be cultured for Mycoplasma or Ureaplasma species in Amies transport media (Copan swab) for shipment to the laboratory (must be refrigerated). Brucella canis must be cultured on brucella blood agar plates. 

One of the most important, but often overlooked, diagnostic procedures in aborting bitches is the examination of aborted fetuses and their membranes. Advise owners to collect these in a clean manner and to refrigerate and present them with the bitch. Brucella canis infection has been reported in people; therefore aborted tissues should be handled with extreme care. 

Histopathologic examination and culture of selected fetal tissues are recommended. Fetal lung and liver tissues are preferred for isolating B. canis organisms. Cultures of fetal stomach contents are beneficial in identifying other bacterial species. Chromosome analysis can be performed in dogs if genetic abnormalities are suspected; however, this analysis is not commonly available. Contact Antech Diagnostics if you have questions concerning appropriate samples and their handling and submission. 

Table 1: Infectious Causes of Canine Abortion

Brucella canis

Most common bacterial cause of abortion in bitches. Abortion occurs between 45-55 days of pregnancy. Infertility follows infection and abortion, vaginal discharges and aborted fetal tissues are highly infectious to other females.

E. coli, S. aureus, Strep. species

Frequently cultured from vaginal discharges or fetal tissues after abortion; their role is unknown. May be associated with infertility, persistent vaginal discharge, and repeat abortion in older females.

ß-hemolytic Streptococcus

Fetal infection has been reported, resulting in abortion or the birth of weak, non­species viable pups.

Mycoplasma and Ureaplasma

Opportunistic organisms normally found in the vaginal canal. In heavy infections, may species cause infertility, early embryonic death, resorption, abortion, stillbirth, or the birth of weak, nonviable pups.

Canine herpesvirus

Causes fatal infections in newborn puppies and vaginitis in bitches. Can cross the placenta and infect puppies, resulting in fetal death, mummification, abortion, premature birth, or the delivery of weak, nonviable pups.

Canine distemper virus

May cause spontaneous abortion with or without fetal infection. Often abortion results from stress of the clinical disease.

Canine adenovirus (infectious hepatitis)

May cause spontaneous abortion with or without fetal infection. Often abortion results from stress of the clinical disease.

Toxoplasma gondii

Protozoal parasite causing mild disease in adult dogs. May be more severe when present with distemper virus, which is known to suppress the immune system. Fetal infection may occur. T. gondii has been found in the milk of lactating bitches.

Neospora caninum

Protozoal parasite resembling T. gondii. Can infect the brains and spinal cords of developing fetuses or neonates. Newborns have progressive muscular weakness leading to death.

Contributed by Jeanette L. Floss, DVM, MS, Dipl. ACT, Indianapolis, IN.


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