Breeding Soundness Examination of Bulls: Standards and Interpretation

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• The Breeding Soundness Examination (BSE) is a multi-faceted assessment predicting a bull's fertility potential, encompassing a physical examination, scrotal circumference measurement, semen collection, and detailed semen evaluation (motility and morphology).
• Semen morphology assessment is critical, with the Society for Theriogenology classifying defects as major (e.g., abnormal heads, proximal droplets) or minor, and requiring at least 70% normal sperm with no more than 20% primary defects for a satisfactory classification.
• Spermatogenesis takes approximately 61 days, meaning insults like fever or trauma will manifest as seminal abnormalities 2-3 months post-event, necessitating careful interpretation of single ejaculates and consideration of recent health history.
• Scrotal circumference is the most reliable non-invasive predictor of sperm production capacity, with age-dependent minimum thresholds (e.g., 30 cm at 12-14 months, 33 cm over 24 months) that must be met for a satisfactory classification.
• Bulls are classified as satisfactory, questionable (deferred), or unsatisfactory potential breeders based on combined physical and seminal findings, with a deferred classification allowing for re-evaluation of transient issues like illness or stress.
• The BSE is a prediction, not a guarantee of fertility; factors such as libido, mating behavior, and subclinical pathology (e.g., abnormal chromatin condensation) can impact breeding success even in bulls passing routine BSE criteria.

The breeding soundness examination (BSE) is the standard method for assessing a bull's potential to achieve pregnancy in a defined breeding season. This article provides a procedural reference for veterinarians performing BSEs in bulls, covering the physical examination, reproductive tract evaluation, semen collection and evaluation, and interpretation of results against established standards. It is written for practicing veterinarians and senior veterinary students who require a structured approach to bull fertility assessment and the clinical reasoning needed to classify bulls as satisfactory, questionable, or unsatisfactory potential breeders.

The BSE serves two distinct purposes. For the individual bull, it identifies physical or seminal abnormalities that would impair fertility. For the herd, it functions as a risk management tool, reducing the economic consequences of a subfertile bull being turned out with a large group of females. The examination must therefore be performed with sufficient rigor that a satisfactory classification carries real predictive weight, while avoiding over-interpretation of findings whose relationship to fertility is weak or unproven.

This article follows the framework used by the Society for Theriogenology and related professional bodies, and it incorporates current evidence on sperm morphology, testicular imaging, and infectious disease screening. Advanced reproductive technologies such as semen freezing, sexed semen production, or in vitro fertilization are outside the scope of this article.

At a Glance

Purpose and Limitations of the Breeding Soundness Examination

The BSE is a prediction of fertility, not a guarantee. A bull classified as a satisfactory potential breeder may still fail to settle females due to mating behavior, libido, or undetected pathology. Conversely, a bull with marginal semen quality may achieve acceptable pregnancy rates when bred to a small number of females under low-demand conditions. The examination identifies animals with a high probability of normal fertility and flags those with conditions likely to impair it.

The Society for Theriogenology publishes the most widely used classification system in North America, and its resources provide the procedural basis for the examination described here. The system assigns bulls to one of three categories based on physical soundness, scrotal circumference, sperm motility, and sperm morphology. A bull must meet minimum standards in all four areas to be classified as satisfactory.

The predictive value of the BSE depends on the quality of the semen evaluation. Morphology assessment, in particular, requires consistent staining technique, adequate magnification, and a systematic classification scheme. Studies of beef bulls in western Canada have shown that approximately 17% of bulls presented for breeding soundness evaluation are classified as unsatisfactory on the basis of sperm morphology alone, with the most common defects being detached heads, distal midpiece reflexes, and bent tails. These findings underscore the importance of a rigorous morphology assessment instead of a cursory scan of the smear.

Reproductive Physiology Relevant to the BSE

Spermatogenesis in the bull takes approximately 61 days from spermatogonial stem cell division to the release of mature spermatozoa into the seminiferous tubule lumen. Epididymal transit adds another 8 to 11 days. This timeline has direct clinical implications: a bull that experiences fever, severe illness, or testicular trauma will not show seminal abnormalities until 2 to 3 months after the insult. A single normal ejaculate does not rule out a recent insult to spermatogenesis, and a single abnormal ejaculate does not confirm permanent infertility.

The testis has a high metabolic demand and a correspondingly high requirement for blood flow. The seminiferous tubules, which constitute 70% to 80% of testicular mass, operate in a relatively hypoxic environment that is essential for normal spermatogenesis. Disruption of testicular perfusion, whether from torsion, trauma, or degenerative disease, rapidly impairs sperm production. Color Doppler ultrasonography has been investigated as a means of assessing testicular blood flow in bulls and other domestic species, and pulsed-wave Doppler velocimetric parameters have shown associations with seminal quality. However, these techniques remain research tools instead of established components of the routine BSE, and their clinical utility is still being defined.

Scrotal circumference is the single best non-invasive predictor of sperm production capacity in the bull. It reflects the mass of functional testicular tissue and is positively correlated with daily sperm output and with the number of sperm in an ejaculate. Scrotal circumference also has a heritable component, so selection for adequate scrotal size has a cumulative effect on herd fertility across generations. Measurement technique matters: the testes should be firmly pushed into the ventral scrotum, and the tape should be placed at the point of maximum circumference, with the tape snug but not compressing the tissue.

Sperm Morphology and Its Relationship to Fertility

Sperm morphology assessment is the most informative component of the semen evaluation, but it is also the most technically demanding. The Society for Theriogenology classification system divides defects into major and minor categories. Major defects are those associated with reduced fertility, including abnormal heads, proximal droplets, abnormal midpieces, and coiled tails. Minor defects, such as distal droplets and bent tails, are less strongly associated with infertility. A bull is classified as unsatisfactory if it has more than 30% total abnormal sperm or more than 20% defective heads.

The interpretation of morphology findings requires an understanding of the origin of specific defects. Some defects arise during spermatogenesis in the testis, while others develop during epididymal transit or during ejaculation. Defects of nuclear condensation, for example, can be detected with Feulgen staining or acridine orange staining, and research has shown that high numbers of abnormally condensed sperm nuclei can occur without an increase in other defects. These nuclear abnormalities can lower fertility, but the effect can be partially compensated by increasing the number of normal spermatozoa in the insemination dose. This finding has practical implications for the interpretation of morphology results: a bull with a high percentage of a single defect type may have a different fertility prognosis than a bull with a similar total percentage of mixed defects.

Breed and age influence the prevalence of sperm abnormalities. In a large study of beef bulls in Alberta, tail defects were more prevalent in Angus and Hereford bulls than in other breeds, while breed, age, and scrotal circumference did not significantly affect the prevalence of head or midpiece defects. These breed differences suggest that breed-specific reference data may be more appropriate than a single universal threshold, although the Society for Theriogenology system remains the standard for classification.

Testicular Imaging and Emerging Techniques

Ultrasonography of the bull reproductive tract is not a required component of the standard BSE, but it can provide valuable information in specific circumstances. B-mode ultrasound allows assessment of testicular parenchymal homogeneity, detection of abscesses, cysts, or neoplasia, and evaluation of the epididymis and accessory sex glands. The technique is well established in stallions, where routine ultrasound evaluation has been shown to detect pathological conditions that impact reproductive performance, including varicocele and thickened vaginal tunics. The application of similar techniques to bulls is reasonable, although the evidence base in cattle is less developed.

Color Doppler ultrasonography has been proposed as a method for quantifying testicular perfusion, and research in domestic animals has demonstrated relationships between Doppler velocimetric parameters and seminal quality. The technique is non-invasive and can be performed during a routine examination, but it requires specialized equipment and training, and the optimal measurement sites and reference values are not yet standardized across breeds and ages. At present, Doppler evaluation of the bull testis should be considered an adjunct to the standard BSE, useful for investigating suspected vascular or degenerative disease instead of for routine screening.

The role of ultrasonography in the BSE is likely to expand as reference data accumulate. For the practicing veterinarian, the immediate value lies in the ability to characterize palpable abnormalities, to confirm or exclude suspected pathology, and to provide the owner with a more precise prognosis than physical examination alone can offer.

Physical Examination and Locomotor Assessment

The physical examination precedes semen collection and follows a fixed sequence. Observe the bull at rest and in motion before handling. Assess body condition, temperament, and gait. Musculoskeletal soundness matters because a bull that cannot mount and thrust effectively will not settle cows regardless of semen quality. Examine the feet and legs for lameness, particularly the hind limbs and stifles. Evaluate the eyes for lesions that impair vision and therefore breeding activity.

Examine the external genitalia systematically. Palpate the scrotum and its contents. The testes should be firm, freely movable within the scrotum, and free of palpable nodules or adhesions. Palpate the epididymides, especially the tail, which should be distinct and resilient. Palpate the spermatic cords for thickening or pain. Examine the penis and prepuce visually and by palpation. Phimosis, balanoposthitis, preputial lacerations, or persistent frenulum are disqualifying or at least require treatment before the bull is used. Examine the internal genitalia by transrectal palpation. The ampullae, vesicular glands, and prostate should be symmetrical and free of enlargement or pain. Seminal vesiculitis is a recognized cause of purulent semen and poor fertility.

Scrotal circumference is measured with a scrotal tape at the widest point, with the testes pulled firmly to the bottom of the scrotum. The measurement is age-dependent and breed-dependent. Minimum acceptable values are published by the Society for Theriogenology and are typically 30 cm at 12 to 14 months, 31 cm at 15 to 18 months, 32 cm at 19 to 24 months, and 33 cm at over 24 months. Scrotal circumference correlates with testicular mass, daily sperm production, and age at puberty in female offspring. A bull below the minimum for his age is a candidate for classification as a satisfactory potential breeder only if all other parameters are excellent, but most protocols require the minimum to be met.

Semen Collection

Semen is collected by electroejaculation or, less commonly, by artificial vagina. Electroejaculation is the standard in practice because it is safe, repeatable, and does not require a teaser animal. Use a rectal probe with three longitudinal electrodes and a rheostat-controlled power source. The bull is restrained in a chute, the rectum is emptied, and the probe is inserted with the electrodes oriented ventrally. Stimulation is delivered in a pattern of increasing voltage, typically 2 to 5 seconds on and 2 to 3 seconds off, with the operator monitoring the bull for signs of discomfort. The penis is extended manually or by the bull's response, and the ejaculate is collected into a warmed, insulated collection cone or artificial vagina liner. The first jets of fluid are often seminal plasma and may contain urine or smegma, the sperm-rich fraction follows.

The electroejaculation protocol should be standardized within a practice. The response to stimulation varies between bulls, and the operator must balance the need for a representative sample against the bull's tolerance. Overstimulation causes pain and can produce a poor sample. The collection equipment must be clean and free of residues, as soap, disinfectant, or water can damage sperm. The sample is kept at body temperature and protected from light, cold shock, and contact with latex.

Semen Evaluation

Evaluate the ejaculate immediately after collection. Record volume, gross motility, and sperm concentration. Volume is read from the graduated collection tube. Gross motility is assessed by placing a drop of semen on a warm slide and examining it at low magnification under a coverslip. A swirling motion indicates good progressive motility. Individual motility is assessed at 200 to 400x magnification on a diluted sample. The Society for Theriogenology requires a minimum of 30% progressively motile sperm, though many practitioners and studs use a higher threshold of 50 to 60%.

Sperm concentration is measured by spectrophotometry, by hemocytometer, or by a commercial counting chamber. Spectrophotometry is rapid and accurate when calibrated for bovine semen. Total sperm per ejaculate is calculated as concentration multiplied by volume. The minimum acceptable total sperm per ejaculate is generally 500 million for a satisfactory classification, though this is a guideline instead of a fixed standard.

Morphology is assessed on a stained smear. Eosin-nigrosin stain is the standard for live-dead determination and morphology. A drop of semen is mixed with a drop of warm stain on a warm slide, smeared, and air-dried. Count at least 100 sperm under oil immersion. Classify defects as primary (head defects, proximal droplets, abnormal midpieces) or secondary (distal droplets, bent tails, detached heads). The Society for Theriogenology classification requires at least 70% normal sperm, with no more than 20% primary defects and no more than 30% total defects. Associations between sperm abnormalities, breed, age, and scrotal circumference in beef bulls reported that 17% of bulls presented for breeding soundness examination were classified as unsatisfactory solely on sperm morphology, with detached heads and distal midpiece reflexes being the most common defects.

Nuclear chromatin condensation is not assessed on routine stained smears. Abnormal chromatin condensation can lower fertility even when conventional morphology is normal, and it may be of epididymal origin. Flow cytometric and microscopic evaluation of abnormal chromatin condensation in bovine sperm nuclei demonstrated that high numbers of abnormally condensed nuclei can occur without an increase in other defects and that the defect can be compensated by increasing the number of normal sperm in the insemination dose. This technique is not part of the standard BSE but is relevant when investigating unexplained subfertility.

Classification and Decision Framework

The Society for Theriogenology classification system assigns bulls to three categories: satisfactory potential breeder, classification deferred, and unsatisfactory potential breeder. A satisfactory bull must pass the physical examination, meet the minimum scrotal circumference for age, and meet the semen thresholds for motility, morphology, and total sperm. A bull that fails any single criterion is classified as unsatisfactory, unless the failure is judged to be temporary or collection-related, in which case classification is deferred and the bull is re-examined in 30 to 60 days.

The deferred category is clinically useful. A bull that is thin, stressed, or recently transported may produce a poor sample that improves on re-testing. A bull with a fever, injury, or recent illness may have a transient decline in semen quality. The spermatogenic cycle in the bull is approximately 61 days, so a bull that suffered a febrile episode will show abnormal sperm for 6 to 8 weeks after the insult. Re-testing at 30 to 60 days is therefore a minimum, and a full recovery may take 90 days.

Breed and age influence the prevalence of sperm abnormalities. Associations between sperm abnormalities, breed, age, and scrotal circumference in beef bulls found that tail defects were more prevalent in Angus and Hereford bulls than in other breeds, and that the percentage of satisfactory bulls ranged from 78.8% in Herefords to 90.6% in Limousins. These differences are not large enough to change the classification thresholds, but they justify caution when evaluating young bulls of breeds known to have slower testicular maturation.

Documentation and Reporting

Record all findings on a standardized BSE form. The form should capture the bull's identification, age, breed, body condition score, scrotal circumference, physical examination findings, semen collection method, ejaculate volume, concentration, total sperm, motility, morphology, and the final classification. Include the date and the veterinarian's signature. The form serves as a legal record and as a baseline for future comparisons.

The classification should be communicated to the owner in writing, with an explanation of any deferred or unsatisfactory findings and a recommended re-test date. For bulls that pass, state the expected breeding load. A satisfactory bull can generally be expected to breed 25 to 40 cows in a natural service setting, but this depends on pasture size, cow-to-bull ratio, and the bull's age and condition. The BSE does not guarantee fertility. It identifies bulls that are likely to be fertile, but a bull can pass a BSE and still have subfertility due to factors not assessed by the examination, such as mating behavior, libido, or immunologic infertility.

The BSE is a point-in-time assessment. A bull that passes in the spring should be re-examined before each subsequent breeding season. Bulls lose condition during breeding, and testicular function declines with age, injury, or disease. Annual examination is the minimum standard for bulls used in natural service.

Recognized Complications and Failure Modes

The BSE can misclassify a bull when a complication is present but undetected. The most consequential failure modes are ejaculatory dysfunction, collection-related artefacts, and subclinical testicular pathology.

Ejaculatory dysfunction presents as failure to mount, failure to ejaculate, or ejaculation of low volume. The discriminating check is a second collection attempt after a rest period. A bull that ejaculates normally on the second attempt after an extended libido test has a behavioral problem, not an organic one. A bull that repeatedly fails to ejaculate despite normal libido warrants examination of the penis, prepuce, and accessory sex glands. Hemospermia or urospermia in the ejaculate indicates a different failure mode, usually balanoposthitis, seminal vesiculitis, or urethral pathology.

Collection artefacts are the most common source of false classification. Poor collection technique produces sperm with artifactual distal midpiece reflexes, bent tails, and detached heads. The discriminating check is repeat collection with proper electroejaculation technique, including adequate stimulation and a clean collection cone. A bull with a high percentage of distal midpiece reflexes on first collection and a normal morphology on second collection had a collection artefact, not a fertility problem.

Subclinical testicular pathology is the most dangerous failure mode because it is silent. Testicular degeneration may be present with normal scrotal circumference and normal palpation findings in early stages. The discriminating check is semen evaluation, specifically the presence of increased numbers of proximal droplets, nuclear vacuoles, or abnormally condensed chromatin. The relationship between abnormal chromatin condensation and reduced fertility has been demonstrated in breeding trials, and this defect can occur without an increase in other sperm abnormalities Dobrinski et al., 1994. Bulls with high numbers of abnormally condensed nuclei may be classified as satisfactory on routine morphology yet have reduced fertility.

Common Errors in Examination and Interpretation

Less experienced clinicians most often err in sperm morphology classification. The most frequent error is overclassifying borderline defects as compensable when they are uncompensable. A distal midpiece reflex is compensable, a proximal droplet in a high percentage is not. The corrective action is to apply the Society for Theriogenology classification strictly and to count at least 100 sperm per smear Menon et al., 2011. Counting fewer than 100 sperm produces unstable estimates of defect prevalence.

A second common error is ignoring the interaction between scrotal circumference and age. A yearling bull with a scrotal circumference of 30 cm may be classified as satisfactory on morphology alone, but the breed and age-adjusted standards exist for a reason. The corrective action is to apply age-adjusted scrotal circumference thresholds and to flag bulls that pass morphology but fail scrotal circumference for re-evaluation.

A third error is failure to examine the penis and prepuce adequately. Many clinicians rely on observation during semen collection and miss preputial adhesions, penile hair rings, or persistent frenulum. The corrective action is a directed examination of the penis and prepuce during collection, including visualization of the glans and the free portion of the penis.

Limitations of Current Evidence

The evidence base for the BSE has significant gaps. The relationship between individual sperm defects and fertility is well established for some defects, such as proximal droplets and nuclear vacuoles, but poorly established for others. The threshold of 30% abnormal sperm for classification as satisfactory is a practical standard, not a biologically derived cutoff. Data from 1,642 beef bull evaluations in Alberta show that 17% of bulls were classified as unsatisfactory on morphology alone, but the fertility consequences of that classification in natural service are not fully quantified Menon et al., 2011.

Expert opinion differs on the role of testicular ultrasound in the BSE. Color Doppler evaluation of testicular blood flow has shown associations with seminal quality in several domestic species, but the technique has not been standardized across breeds, seasons, or measurement locations Velasco and Ruiz, 2020. The clinical utility of Doppler parameters for predicting fertility in individual bulls remains uncertain, and the technique is not yet part of the standard BSE Samir et al., 2021.

Infectious disease screening is another area of evolving evidence. Bovine leukemia virus provirus has been detected in smegma of infected bulls but not in semen, suggesting that venereal transmission risk may be lower than previously assumed Benitez et al., 2019. However, the sample size was limited, and the clinical significance for herd biosecurity remains debated.

Referral, Consultation, and Regulatory Reporting

Referral to a theriogenology specialist is warranted when a bull fails the BSE on repeated examination without an identifiable cause, when testicular pathology is suspected but cannot be confirmed with available imaging, or when a bull has a history of normal fertility but fails a current BSE. Specialist evaluation may include testicular biopsy, advanced semen analysis, or hormonal profiling.

Laboratory involvement is indicated for specialised semen evaluation, including chromatin structure assays, when routine morphology is normal but fertility is suspected to be reduced. The sperm chromatin structure assay using acridine orange and flow cytometry provides a quantitative measure of abnormal chromatin condensation that correlates with Feulgen staining Dobrinski et al., 1994.

Regulatory reporting obligations vary by jurisdiction. Veterinarians should be aware of reportable diseases in their region and of international trade requirements for bulls intended for export. The World Organization for Animal Health maintains terrestrial animal health standards that apply to international movement of breeding animals WOAH terrestrial animal health standards. Practitioners should consult current regional requirements before certifying bulls for interstate or international movement.

Frequently Asked Questions

How Should I Proceed When a Bull Fails the Physical Examination but Passes Semen Evaluation?

A bull that fails physical examination cannot be classified as a satisfactory potential breeder regardless of semen quality. The physical examination is the first gate in the sequential BSE process. Common physical failures include lameness, ocular lesions, penile abnormalities, and excessive body condition that impairs mounting ability. These conditions may be temporary or correctable. Document the specific defect, estimate its impact on breeding capacity, and recommend a recheck interval appropriate to the lesion. For example, a bull with mild lameness may be re-examined in 30 days, whereas a bull with a persistent penile hematoma may require surgical assessment. Refer to Society for Theriogenology resources for current classification standards and recheck recommendations.

What Minimum Equipment Is Required to Perform a Defensible BSE in Field Conditions?

A functional chute or head gate, a rectal sleeve and lubricant, an electroejaculator or service cow for collection, glass slides, eosin-nigrosin stain, a microscope with 400x and 1000x magnification, and a scrotal tape are the core requirements. A phase-contrast microscope improves morphology assessment but is not mandatory if eosin-nigrosin smears are prepared properly. If an electroejaculator is unavailable, collection by artificial vagina requires a trained teaser animal and handler. When equipment is limited, prioritize scrotal circumference measurement, physical examination, and a stained smear for morphology over accessory gland evaluation. Record any equipment limitations in the report. The MSD Veterinary Manual provides guidance on standard BSE procedures and equipment expectations.

How Do I Interpret a BSE in a Bull Younger Than 12 Months?

Yearling bulls often have smaller scrotal circumference and higher percentages of proximal cytoplasmic droplets than mature bulls. The Society for Theriogenology standards were developed primarily for bulls 12 months and older. For bulls younger than 12 months, report the raw data and compare against age-matched reference values instead of applying adult thresholds. A scrotal circumference below the minimum for age does not automatically classify the bull as unsatisfactory, but it warrants a recheck at 12 to 14 months. Proximal droplets above 20% in a yearling may resolve with sexual maturity. Advise the client that a definitive classification should wait until the bull reaches 12 to 14 months of age. Consult Society for Theriogenology resources for age-specific reference tables.

What Should I Tell a Producer Whose Bull Has Marginal Semen Quality?

Frame the conversation around risk instead of a binary pass-fail label. A bull with 25% abnormal sperm, for example, is not sterile, but his fertility is likely reduced relative to a bull with 10% abnormalities. Explain that conception rates may be acceptable in a single-sire, low-pressure breeding season but could fail in a multi-sire pasture or a synchronised timed-AI program. Recommend a recheck in 60 days, as spermatogenesis takes approximately 61 days and transient stressors may resolve. If the bull is valuable genetically, discuss semen collection and cryopreservation as an alternative. Note that abnormal chromatin condensation can lower fertility even when routine morphology appears acceptable, as described in flow cytometric evaluation of bovine sperm nuclei.

How Should I Document a BSE When the Owner Declines Recommended Tests?

Document the declined tests explicitly in the medical record and in the written report to the owner. State which components of the standard BSE were performed, which were omitted, and the reason given by the owner. Classify the bull only on the basis of completed tests, and add a clear statement that the classification is provisional pending the omitted evaluations. For example, if the owner declines semen collection, the report should state that physical examination and scrotal circumference were normal but that the bull cannot be classified as a satisfactory potential breeder without semen evaluation. This documentation protects you if the bull is later used heavily and fertility problems arise. The AVMA practice resources offer guidance on medical record standards.

Does a Bull That Passes a BSE Guarantee Normal Fertility?

No. A satisfactory classification indicates that the bull meets minimum thresholds for physical soundness, scrotal circumference, and semen quality at the time of examination. It does not predict fertility with certainty. Bulls can develop injuries, infections, or degenerative conditions after the examination. Seasonal heat stress can transiently depress semen quality for several weeks. Additionally, the BSE does not assess libido, mating behavior, or serving capacity under natural conditions. Some bulls with normal semen quality fail to breed cows effectively due to behavioral issues. The correlation between BSE results and field fertility is imperfect, and breed, age, and individual variation influence outcomes, as shown in associations between sperm abnormalities, breed, age, and scrotal circumference. Recommend annual re-examination before each breeding season.

Related Clinical & Scientific Guides

• Diagnostic Approach to Canine Infertility in the Bitch
• Canine Neonatal Resuscitation: Protocol and Monitoring
• Equine Breeding Soundness Examination of the Stallion

References and Further Reading

• Flow cytometric and microscopic evaluation and effect on fertility of abnormal chromatin condensation in bovine sperm nuclei.. 1994.
• New Approaches to Assess Fertility in Domestic Animals: Relationship between Arterial Blood Flow to the Testicles and Seminal Quality.. 2020.
• Associations between sperm abnormalities, breed, age, and scrotal circumference in beef bulls.. 2011.
• Advances in applications of color Doppler ultrasonography in the andrological assessment of domestic animals: A review.. 2021.
• Breeding bulls as a potential source of bovine leukemia virus transmission in beef herds.. 2019.
• Diagnostic applications of ultrasonography to stallion's reproductive tract.. 2005.
• Society for Theriogenology Resources. Society for Theriogenology.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.
• American Veterinary Medical Association Practice Resources. American Veterinary Medical Association.

Related Articles

• Breeding Soundness Examination of the Canine Male
• Equine Breeding Soundness Examination: Mare Evaluation
• Equine Breeding Soundness Examination of the Stallion
• Bovine Reproductive Ultrasonography: Applications and Interpretation
• Feline Breeding Management: Estrus Detection and Mating

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.