# Pregnancy Diagnosis in the Bitch: Methods and Interpretation


## Key Takeaways

- Canine pregnancy diagnosis requires careful timing due to the species' unique reproductive physiology; palpation, ultrasonography, and relaxin assays each have specific windows of reliability and failure modes.
- Ultrasonography is the most versatile method, confirming pregnancy as early as day 20 post-ovulation, assessing fetal viability via heartbeat detection by days 23-25, and estimating gestational age through fetal measurements.
- Relaxin is the only practical pregnancy-specific hormone assay for bitches, detectable from days 22-27 post-LH surge, but it confirms placental presence, not fetal viability or litter size.
- Progesterone assays are not diagnostic for pregnancy in bitches, as progesterone levels remain elevated throughout the luteal phase in both pregnant and non-pregnant states; they are useful for ovulation timing and luteal support monitoring.
- Radiography is primarily useful in the final third of gestation (after day 45) for accurate fetal counting and assessing skeletal maturation, guiding decisions for elective cesarean sections.
- Common errors include over-interpreting early negative results (e.g., ultrasound before day 21, relaxin before day 25) and misidentifying uterine fluid or other abdominal structures; repeat testing at appropriate intervals is crucial for accurate diagnosis.

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Pregnancy diagnosis in the bitch presents a distinct clinical challenge because the reproductive physiology of the dog diverges from that of most domestic species. The clinician must select among palpation, ultrasonography, and hormonal assays, each with a defined window of reliability and characteriztic failure modes. This article provides a procedural comparison of these methods for the practicing veterinarian, with emphasis on timing, accuracy, and interpretation within the context of the canine estrous cycle.

The reader is assumed to be a qualified veterinary professional who can integrate these techniques into a breeding management program. The clinical questions addressed are direct: when can pregnancy be confirmed, which method is most appropriate at a given gestational stage, and how should equivocal results be interpreted? The article also covers the physiologic basis for each diagnostic approach, because a method applied outside its valid window produces misleading results.

## At a Glance

| Parameter | Palpation | Ultrasonography | Relaxin assay |
|---|---|---|---|
| Earliest reliable detection | Day 21 to 24 post ovulation | Day 20 to 25 post ovulation | Day 22 to 25 post ovulation |
| Optimal window | Day 28 to 35 | Day 25 to 40 for confirmation, serial imaging for viability | Day 28 or later for high sensitivity |
| Confirms fetal viability | No | Yes, via heartbeat detection | No |
| Confirms fetal number | Unreliable | Reliable after day 28, accuracy varies with litter size | No |
| Provides gestational age estimate | No | Yes, via fetal measurements | No |
| Principal limitation | High false negative rate, obesity, tense abdomen | Operator dependent, requires training | Cannot distinguish viable from nonviable pregnancy |
| Key interpretation caveat | Uterine fluid can mimic pregnancy | Anembryonic vesicles may be seen before day 23 | Progesterone is not a pregnancy test in the bitch |

## Physiologic Basis for Diagnostic Timing

The canine pregnancy is short, and accurate gestational dating depends on understanding the endocrine events that precede implantation. Ovulation occurs approximately 48 hours after the luteinizing hormone surge, and oocytes require an additional 2 to 3 days to mature before fertilization. The corpora lutea secrete progesterone throughout diestrus in both pregnant and nonpregnant bitches, so plasma progesterone concentrations do not discriminate between these states. This fundamental point underpins why progesterone measurement, although essential for ovulation timing, has no role as a pregnancy test in the dog. As reviewed in the endocrinology of pregnancy in the dog, increased progesterone secretion in pregnant animals follows implantation and relaxin secretion by the feto-placental units, and no placental source of progesterone has been identified.

Relaxin is the only practical pregnancy-specific hormone currently measurable in the bitch. It is produced by the feto-placental unit, and its appearance in maternal plasma coincides with implantation. Prolactin secretion increases in response to relaxin production, independent of estrogen, and prolactin becomes absolutely required for luteal maintenance as gestation progresses. The respective roles of LH, FSH, and prolactin remain incompletely defined, with conflicting evidence across studies, but this does not affect the clinical utility of relaxin as a pregnancy marker.

Pre-implantation events remain poorly characterized in the bitch, and no embryonic factors have been isolated that would permit earlier diagnosis. This physiologic gap explains why no method currently available can detect canine pregnancy before approximately day 20 post ovulation.

## Palpation

Abdominal palpation is the oldest method of pregnancy diagnosis in the bitch and remains useful when performed within its narrow optimal window. Uterine swellings, representing the embryonic vesicles, become palpable as discrete, tense, fluid-filled enlargements between day 21 and day 24 after ovulation. The optimal palpation window is day 28 to 35, when the swellings are largest relative to the surrounding uterine tissue and before they coalesce into a single elongated mass.

The technique requires a relaxed bitch in a standing or lateral position. The clinician palpates gently but deliberately, sweeping the abdomen from caudal to cranial while identifying the uterine horns between the bladder and the colon. The swellings feel like a string of beads, and their number does not reliably predict litter size because of overlapping loops of intestine and the limited field of palpation.

The principal limitation is the false negative rate. Obesity, a tense abdominal wall, or a nervous bitch can render the uterus impalpable. Uterine fluid accumulation from cystic endometrial hyperplasia or pyometra can produce swellings that mimic pregnancy. Conversely, a small litter may produce swellings too subtle to detect. Palpation cannot confirm fetal viability, and it provides no estimate of gestational age. For these reasons, palpation is best used as a screening tool in the hands of an experienced clinician, with ultrasonography reserved for confirmation.

## Ultrasonography

Ultrasonography is the most versatile method for canine pregnancy diagnosis because it can confirm pregnancy, assess fetal viability, estimate gestational age, and detect fetal maturation. Transabdominal scanning with a 5 to 10 MHz transducer is standard. The bitch is examined in dorsal or lateral recumbency, and the hair coat is clipped or wetted with alcohol to ensure acoustic coupling.

The earliest detectable sign of pregnancy is the gestational sac, an anechoic fluid-filled structure within the uterine lumen, visible from approximately day 20 post ovulation. The embryonic vesicle appears as a small echogenic thickening within the sac. Fetal heartbeat is typically detectable by day 23 to 25, and its presence confirms a viable pregnancy. Before day 23, anembryonic vesicles can be seen, and a single examination at this stage may produce a false positive if the vesicle fails to develop. Serial examinations are therefore recommended when an early diagnosis is required.

Fetal number can be estimated after day 28, but accuracy declines with large litters because of overlapping fetal structures. Gestational age estimation relies on serial measurements of fetal structures, including the crown-rump length in early gestation and the biparietal diameter and organ dimensions later. As reviewed in the literature on estimation of gestational age and assessment of canine fetal maturation using radiology and ultrasonography, breeding dates alone do not provide due dates with adequate accuracy, and imaging-based dating is particularly valuable when ovulation timing is absent. Ultrasonography also permits assessment of fetal maturation near term, which guides the timing of elective cesarean section in high-risk pregnancies.

The principal limitations are operator dependence and the cost of equipment. A clinician who does not scan canine pregnancies regularly will have lower sensitivity and may misidentify uterine fluid as gestational sacs.

## Hormonal Assays

Endocrine testing offers the earliest non-imaging confirmation of pregnancy, but interpretation requires a clear understanding of what each analyte does and does not indicate. Progesterone measurement has no role in pregnancy diagnosis. As reviewed by Verstegen-Onclin and Verstegen in their [review of canine pregnancy endocrinology](https://pubmed.ncbi.nlm.nih.gov/18556055/), plasma progesterone concentrations are similar in pregnant and non-pregnant bitches throughout the luteal phase, so a single progesterone value cannot distinguish gravid from non-gravid animals. Progesterone testing remains useful for ovulation timing and for monitoring luteal support in bitches with a history of pregnancy loss, but it should never be used to answer the question "is this bitch pregnant?"

Relaxin is the only practical hormonal marker of pregnancy in the bitch. It is secreted by the feto-placental units after implantation, and commercially available qualitative and quantitative immunoassays detect it in serum or plasma. Relaxin becomes detectable between days 22 and 27 after the luteinizing hormone surge, depending on the assay. A positive result before day 22 should be treated with caution, as false negatives are common at this stage. A negative relaxin test performed at or after day 30 is highly reliable for ruling out pregnancy, provided the bitch is not experiencing fetal resorption or abortion at the time of sampling. A positive result confirms that placental tissue is present and functional, but it does not confirm fetal viability, litter size, or the absence of fetal death.

The same endocrinology review notes that prolactin secretion increases in response to relaxin production, and that prolactin becomes the primary luteotropic support in the second half of gestation. Prolactin measurement has no role in pregnancy diagnosis and is reserved for research or for investigating specific luteal insufficiency syndromes.

Practical assay selection depends on the clinical question. A qualitative relaxin test is appropriate when the owner simply needs confirmation of pregnancy. A quantitative relaxin assay adds little clinical information beyond the qualitative result, because relaxin concentrations do not correlate reliably with litter size or fetal viability. If the clinical question involves fetal health, ultrasound is the superior tool. If the question is whether the bitch is pregnant at all, relaxin testing at day 30 or later is simple, inexpensive, and accurate.

## Radiography

Radiography becomes useful only in the final third of gestation, after fetal skeletons have mineralised. The [review of gestational age estimation and fetal maturation by Lopate](https://pubmed.ncbi.nlm.nih.gov/18534674/) describes the timing of skeletal mineralisation and its clinical application. Vertebral bodies and ribs are typically visible from day 45 after the luteinizing hormone surge, with the skull and long bones becoming more distinct over the following days. By day 50, fetal skeletons are reliably visible in most bitches.

The primary indications for radiography are not early diagnosis but rather fetal counting, fetal maturation assessment, and detection of fetal death. A radiograph taken after day 55 can provide an accurate fetal count, which is valuable when ultrasound has been inconclusive or when dystocia is anticipated. Radiographic signs of fetal death include loss of the normal fetal posture, overlapping of skull bones, and the presence of gas within the uterus or within a fetus. These findings are not always reliable, and a single radiograph cannot exclude fetal death with certainty.

Radiography also contributes to the decision to perform an elective cesarean section. The Lopate review emphasizes that breeding dates alone do not provide adequate accuracy for due date prediction, and that radiographic assessment of fetal maturation is necessary when ovulation timing is lacking. The appearance of mineralised fetal teeth is a specific indicator of pulmonary maturity, and their presence supports a decision to proceed with delivery. In high-risk pregnancies where the bitch is receiving supplemental progesterone, radiographic confirmation of fetal maturation guides the timing of progesterone withdrawal so that delivery occurs at a point where fetal survival is likely.

The correct choice between radiography and ultrasound depends on gestational age and the clinical question. Ultrasound provides earlier diagnosis and superior assessment of fetal viability, but radiography provides a more reliable fetal count in late gestation and is less operator dependent. A bitch with a suspected singleton fetus or oversize fetuses, as described in the Lopate review, benefits from late-gestation radiography to inform the cesarean decision.

## Method Comparison and Selection

| Method | Earliest reliable detection | Sensitivity | Practical considerations | Primary clinical use |
|---|---|---|---|---|
| Palpation | Day 21 to 28 | Moderate, operator dependent | Requires relaxed bitch, false positives from uterine fluid, false negatives from small litters or obesity | Rapid screening in cooperative patients |
| Ultrasound | Day 21 to 25 for gestational sac, day 25 to 28 for embryo heartbeat | High after day 28 | Requires equipment and training, provides viability and count, operator dependent | Confirmation, viability, gestational aging, litter count |
| Relaxin assay | Day 22 to 27 | High after day 30 | Simple, inexpensive, no imaging needed, does not assess viability or count | Confirmation when ultrasound is unavailable |
| Radiography | Day 45 to 50 | High for fetal count after day 55 | Provides fetal count and maturation, no viability information | Late-gestation count, maturation, cesarean planning |

The selection algorithm begins with the date of the luteinizing hormone surge or ovulation, when known. If the bitch is at day 25 or later and ultrasound is available, it is the method of choice. If ultrasound is not available, a relaxin test at day 30 or later provides reliable confirmation. If the bitch is at day 45 or later and the question is fetal count or maturation, radiography is indicated. Palpation is reserved for situations where imaging and laboratory testing are unavailable, and its limitations must be communicated to the owner.

Patient status changes the algorithm. A bitch with a history of fetal resorption or pregnancy loss benefits from early ultrasound to confirm viability, also a positive relaxin test. An obese bitch is a poor palpation candidate. A valuable litter with known breeding dates may justify serial ultrasound examinations to monitor fetal growth. A bitch with a single fetus, as noted in the Lopate review, requires late-gestation radiography to confirm fetal size before a planned cesarean.

## Documentation and Monitoring

Every pregnancy diagnosis should be documented with the method used, the gestational age at the time of examination, and the specific findings. For ultrasound, record the number of gestational sacs, the presence or absence of embryonic heartbeat, the crown-rump length or other biometric measurements, and any abnormalities such as fetal fluid accumulation or placental separation. For radiography, record the fetal count, the presence of mineralised teeth, and any signs of fetal death. For relaxin testing, record the assay used and the result, and note the gestational age at sampling.

Serial monitoring is indicated when the pregnancy is high risk, when the bitch has a history of reproductive failure, or when the owner requests confirmation of fetal viability. Ultrasound examinations performed at weekly intervals from day 25 to day 45 can document fetal growth and cardiac activity. After day 45, radiography can confirm fetal count and maturation. The Lopate review notes that in cases where ovulation timing is lacking, gestational age estimation at the time of pregnancy diagnosis, or closer to term, is necessary to plan delivery. This is particularly relevant for bitches receiving progesterone supplementation, where the timing of medication withdrawal must be coordinated with confirmed fetal maturation.

The distinction between confirming pregnancy and confirming fetal health must be maintained throughout. A positive relaxin test confirms placental presence. A visible heartbeat confirms fetal life at that moment. A radiograph showing mineralised skeletons confirms that the fetuses have reached a developmental stage compatible with survival. Each method answers a different question, and the clinician should select the method that answers the question the owner is actually asking.

## Recognized Complications and Early Detection

Pregnancy loss in the bitch is frequently silent. Resorption may occur without vulvar discharge or systemic signs, particularly before day 45. Ultrasonography at 28 to 35 days provides the first reliable opportunity to confirm fetal viability through detection of heartbeat motion. A litter that appears normal at first examination may still undergo partial or complete resorption, so repeat imaging at 45 to 50 days is advised when breeding management depends on confirmed pregnancy.

Failure to detect pregnancy at an expected time point does not always indicate loss. Bitches examined before day 21 may have conceptuses too small for reliable identification, and an apparently empty uterus at day 25 can still yield a normal litter. The reverse error also occurs: the uterine enlargement of pyometra or mucometra can be mistaken for gestational sacs by an inexperienced sonographer. Discriminating features include the absence of embryonic poles, lack of heartbeat motion, and the characteriztically tubular instead of spherical shape of a fluid-distended uterus.

Fetal death after day 45 is more readily recognized. Loss of heartbeat motion, collapse of the thoracic cavity, overlapping skull bones, and loss of normal fetal contours are sonographic indicators. Radiography can contribute late in gestation: loss of the normal fetal skeletal alignment or the presence of intrafetal gas suggests maceration. The [review of canine fetal maturation using radiology and ultrasonography](https://pubmed.ncbi.nlm.nih.gov/18534674/) notes that radiographic assessment of fetal skeletal development is most useful in the final week before whelping, when mineralisation of specific structures becomes visible.

## Common Errors and Corrective Action

The most frequent error in canine pregnancy diagnosis is overinterpreting a single negative result. A negative ultrasound examination before day 21, a negative relaxin assay before day 25, or a negative palpation before day 24 does not exclude pregnancy. The corrective action is to schedule a repeat examination at the appropriate gestational window instead of advising the owner that the bitch is open.

Palpation errors follow a predictable pattern. Novice examiners mistake uterine edema or fluid accumulation for gestational swellings, or they palpate the kidneys and mistake them for fetuses. The swellings of pregnancy are discrete, symmetrical, and arranged in a chain within the uterine body and horns. Kidneys are larger, more cranial, and not movable within the abdomen. When palpation is equivocal, ultrasound should be the arbiter.

Ultrasound errors include misidentifying the urinary bladder as a gestational sac, failing to distinguish the uterine body from the colon, and using excessive transducer pressure that compresses the uterus against the body wall. The bladder has a thin, uniform wall and no internal structure, whereas a gestational sac contains an embryo with visible heartbeat from day 23 onward. The [endocrinology of pregnancy in the dog](https://pubmed.ncbi.nlm.nih.gov/18556055/) emphasizes that pre-implantation events remain poorly defined and no embryonic factors have been isolated, which is why hormonal diagnosis before implantation is not possible.

Relaxin assay errors are usually timing errors. Testing before day 25 produces false negatives because placental relaxin secretion has not yet reached assay threshold. Testing after day 60 can produce false negatives in some assays as relaxin concentrations decline near term. The corrective action is to confirm the assay's validated window and to pair a negative result with ultrasound when clinical suspicion remains high.

| Observation | Likely cause | Discriminating check |
|---|---|---|
| Negative ultrasound before day 21 | Conceptuses too small to resolve | Repeat at day 28 to 35 |
| Negative relaxin before day 25 | Assay before placental secretion threshold | Repeat after day 30 |
| Uterine fluid without embryos | Pyometra, mucometra, or early pregnancy | Repeat in 5 to 7 days, look for heartbeat |
| Palpable swellings, negative ultrasound | Fecal mass, kidney, or uterine pathology | Confirm with ultrasound |
| Fetal heartbeat absent after day 28 | Fetal death or incorrect dating | Repeat in 48 hours, assess litter mates |

## Evidence Limitations and Divergent Expert Opinion

The evidence base for canine pregnancy diagnosis is thinner than for production species. Comparative reviews of pregnancy diagnosis methods in cattle, such as the [review of early pregnancy diagnosis in bovines](https://pubmed.ncbi.nlm.nih.gov/24382949/), illustrate the range of sensitivity and specificity achievable across methods, but these figures cannot be extrapolated directly to the bitch. Canine studies are smaller, often use different gestational dating schemes, and rarely report sensitivity and specificity with confidence intervals.

Expert opinion diverges on the optimal timing for a single confirmatory examination. Some authorities recommend a single ultrasound at day 28 to 30, arguing that this balances detection reliability against the need for early confirmation. Others prefer day 25, accepting a small false-negative rate in exchange for earlier owner notification. Both positions are defensible, the choice depends on whether the owner needs early confirmation for management decisions or can wait for a more definitive result.

The role of progesterone measurement in pregnancy diagnosis remains contested. Progesterone concentrations do not distinguish pregnant from non-pregnant bitches because luteal function is similar in both states, as noted in the [review of canine pregnancy endocrinology](https://pubmed.ncbi.nlm.nih.gov/18556055/). Progesterone is valuable for monitoring luteal sufficiency in bitches with a history of pregnancy loss, but it is not a pregnancy test.

## Referral and Escalation Criteria

Most pregnancy diagnoses are completed in general practice without specialist input. Referral to a theriogenologist or veterinary radiologist is warranted when ultrasound findings are ambiguous despite adequate equipment and experience, when fetal death is suspected but the owner requires confirmation before deciding on intervention, or when gestational dating is critical for planned caesarean section and breeding dates are unknown.

Laboratory involvement is indicated when relaxin assay results conflict with ultrasound findings, when serial progesterone monitoring is required for a bitch with suspected luteal insufficiency, or when a non-pregnant bitch has persistent uterine fluid and hormonal testing is needed to distinguish pyometra from other causes.

Regulatory reporting is rarely relevant to routine pregnancy diagnosis in companion animals. However, veterinarians working with endangered canids, wildlife rehabilitation programs, or assisted reproductive technology involving non-domestic species should be aware that [standards published by the World Organization for Animal Health](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) may apply to the movement, breeding, or export of these animals. The use of ultrasound to confirm pregnancy in surrogate canids has been documented in conservation programs, and the same imaging standards apply regardless of species.

## Frequently Asked Questions

### How should I proceed when high-frequency ultrasound is unavailable for early pregnancy diagnosis?

When high-frequency equipment is unavailable, rely on a combination of methods that compensate for individual limitations. Palpation between days 21 and 28 provides a rapid screening but cannot distinguish pregnancy from pyometra or other uterine enlargement. A relaxin assay performed after day 28 offers high specificity for pregnancy, as relaxin is produced only by the feto-placental unit. Radiography after day 45 confirms fetal skeletal mineralization and provides fetal counts, though it cannot diagnose pregnancy earlier. The [Society for Theriogenology resources](https://www.therio.org/) include practical guidance on method selection under varying equipment constraints. Document the methods used and their timing so that gestational age estimates account for the reduced sensitivity of lower-frequency transducers.

### What is the most reliable way to confirm pregnancy when ultrasound findings are equivocal?

Equivocal ultrasound findings most often arise from examinations performed before day 20, when embryonic vesicles are small and easily missed, or from maternal obesity and patient motion degrading image quality. Repeat the ultrasound examination 5 to 7 days later, as gestational sacs and embryonic structures develop rapidly during this window. If repeat imaging remains inconclusive, a relaxin assay performed after day 28 provides a definitive answer, since false positives are rare when the assay is run correctly. The [endocrinology of pregnancy in the dog](https://pubmed.ncbi.nlm.nih.gov/18556055/) confirms that relaxin secretion by the feto-placental units begins after implantation, making it a reliable pregnancy-specific marker. Correlate the imaging findings with breeding dates and ovulation timing when available.

### How do I explain a false negative relaxin result to a concerned breeder?

A false negative relaxin result usually reflects testing too early, before feto-placental relaxin production reaches detectable concentrations. Sampling before day 28 of gestation is the most common cause. Less frequently, a single pup litter produces lower relaxin concentrations that fall below the assay's detection threshold. Explain that the test measures a pregnancy-specific hormone, not a hormone present in all bitches regardless of pregnancy status, and that repeat testing in 5 to 7 days is the standard approach. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides background on assay interpretation that supports client discussions. Advise the breeder that ultrasound remains the preferred confirmatory method when timing is uncertain.

### What records should I maintain for serial pregnancy monitoring?

Record the breeding dates, ovulation timing results if available, and the date and method of each pregnancy examination. For ultrasound, document the transducer frequency, the structures identified, and measurements such as crown-rump length or gestational sac diameter. For radiography, record the number of fetal skeletons visible and the degree of mineralization. Note any complications, including suspected fetal loss or maternal illness, with the date of detection. The [Society for Theriogenology resources](https://www.therio.org/) emphasize that complete reproductive records support accurate gestational age estimation and delivery planning. Provide the breeder with a written summary of findings and the estimated whelping date, and update this summary after each examination.

### How does pregnancy diagnosis differ in a maiden bitch compared with a multiparous bitch?

Maiden bitches often have tighter uterine tone and smaller uterine horns, which can make early palpation more challenging and increase the risk of false negative findings. Their smaller body size, particularly in toy breeds, may limit the utility of transabdominal ultrasound due to reduced acoustic windows. Multiparous bitches frequently have uterine laxity from previous pregnancies, which can make palpation findings less specific and ultrasound interpretation more dependent on identifying discrete gestational structures instead of uterine enlargement alone. Relaxin assays are unaffected by parity and provide a consistent diagnostic option across both groups. The [estimation of gestational age using radiology and ultrasonography](https://pubmed.ncbi.nlm.nih.gov/18534674/) notes that fetal measurements are reliable regardless of parity, supporting their use when breeding dates are unknown.

### What should I tell a client who asks about at-home pregnancy testing kits?

At-home relaxin test kits are available, but their accuracy depends on correct sample handling, appropriate timing, and strict adherence to the manufacturer's instructions. Advise clients that testing before day 28 risks false negatives and that a negative result does not exclude pregnancy. A positive result from a home kit should be confirmed with ultrasound, which provides fetal viability assessment and fetal counts that a hormone assay cannot offer. The [endocrinology of pregnancy in the dog](https://pubmed.ncbi.nlm.nih.gov/18556055/) explains that relaxin is pregnancy-specific, which supports the biologic basis of these tests, but assay performance varies between manufacturers. Recommend that clients schedule an in-clinic ultrasound between days 25 and 35 for confirmation and gestational age estimation.

## Related Clinical & Scientific Guides

* [Diagnostic Approach to Canine Infertility in the Bitch](/knowledge/veterinary-medicine/theriogenology/diagnostic-approach-to-canine-infertility-in-the-bitch)
* [Canine Neonatal Resuscitation: Protocol and Monitoring](/knowledge/veterinary-medicine/theriogenology/canine-neonatal-resuscitation-protocol-monitoring)
* [Equine Breeding Soundness Examination of the Stallion](/knowledge/veterinary-medicine/theriogenology/equine-breeding-soundness-examination-of-the-stallion)


## References and Further Reading

- [Estimation of gestational age and assessment of canine fetal maturation using radiology and ultrasonography: a review.](https://pubmed.ncbi.nlm.nih.gov/18534674/). 2008.
- [Endocrinology of pregnancy in the dog: a review.](https://pubmed.ncbi.nlm.nih.gov/18556055/). 2008.
- [Early pregnancy diagnosis in bovines: current status and future directions.](https://pubmed.ncbi.nlm.nih.gov/24382949/). 2013.
- [Strategies for improving fertility in the modern dairy cow.](https://pubmed.ncbi.nlm.nih.gov/16280156/). 2006.
- [Endangered wolves cloned from adult somatic cells.](https://pubmed.ncbi.nlm.nih.gov/17386020/). 2007.
- [Prevalence of bovine subclinical endometritis 4h after insemination and its effects on first service conception rate.](https://pubmed.ncbi.nlm.nih.gov/18801562/). 2009.
- [Society for Theriogenology Resources](https://www.therio.org/). Society for Theriogenology.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.

## Related Articles

- [Pregnancy Diagnosis in Cattle: Methods and Accuracy](/knowledge/veterinary-medicine/theriogenology/pregnancy-diagnosis-in-cattle-methods-and-accuracy)
- [Equine Pregnancy Diagnosis: Methods and Clinical Application](/knowledge/veterinary-medicine/theriogenology/equine-pregnancy-diagnosis-methods-and-clinical-application)
- [Ovine Pregnancy Diagnosis: Transabdominal Ultrasound and Management](/knowledge/veterinary-medicine/theriogenology/ovine-pregnancy-diagnosis-transabdominal-ultrasound-management)
- [Uterine Infections in the Bitch: Diagnosis and Management](/knowledge/veterinary-medicine/theriogenology/uterine-infections-in-the-bitch-diagnosis-and-management)
- [Canine Pregnancy Diagnosis: Ultrasound and Hormonal Assays](/knowledge/veterinary-medicine/theriogenology/canine-pregnancy-diagnosis-ultrasound-hormonal-assays)

> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.