# Equine Reproductive Anatomy: Stallion and Mare


## Key Takeaways

- The stallion's testes are housed within the scrotum, with their long axis oriented horizontally, and are suspended by the mesorchium which carries vital vascular and ductal structures; failure of descent results in cryptorchidism, requiring specific surgical approaches guided by laparoscopic visualization of the vaginal ring and mesorchium.
- The mare's ovaries remain abdominal, suspended by the mesovarium, and are characterized by a unique ovulation fossa; the ovarian artery and vein within the mesovarium are critical surgical landmarks, and the close proximity of the uterine tube's infundibulum to the fossa is essential for oocyte capture.
- Stallion accessory sex glands (ampullae, vesicular, prostate, bulbourethral) contribute seminal plasma, crucial for sperm viability and modulation of the mare's reproductive tract environment, with the ampullae being palpable per rectum.
- The mare's cervix acts as a vital barrier against ascending infection, and its competence is paramount for pregnancy maintenance; the vulvar seal and vestibulovaginal junction are primary defenses against contamination, with vulvar conformation influencing risk of pneumovagina.
- Reproductive tract infections in mares, commonly caused by *Streptococcus equi* subspecies *zooepidemicus* and *Escherichia coli*, necessitate culture and susceptibility testing for targeted antimicrobial therapy, often involving uterine lavage due to poor concentration of systemic antimicrobials in the endometrium.
- Common diagnostic errors include misinterpreting the equine corpus luteum as a tumor and failing to differentiate clitoral sinuses from the urethral orifice during endoscopic examination, which can lead to false-negative cultures for venereal pathogens like *Taylorella equigenitalis*.

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This article reviews the clinically relevant reproductive anatomy of the stallion and the mare, with emphasis on structures that inform breeding management, diagnostic evaluation, and surgical decision making. It is written for veterinary students and practitioners who require a working knowledge of topographic relationships, vascular supply, and functional histology. The content integrates gross dissection findings with laparoscopic observations and addresses how anatomic features predispose the horse to specific reproductive disorders.

A working command of reproductive anatomy underpins every aspect of equine theriogenology, from routine breeding soundness examination to emergency laparotomy. The clinician who cannot predict the course of the ductus deferens or the suspension of the ovary will struggle to interpret rectal palpation, ultrasonography, or surgical findings. This reference provides that foundation and directs attention to structures most frequently implicated in disease.

## At a Glance

| Structure | Stallion | Mare |
|---|---|---|
| Gonadal position | Scrotum, inguinal region | Caudal abdomen, near sublumbar region |
| Gonadal axis | Testis, long axis horizontal | Ovary, ovulation fossa oriented laterally |
| Internal tubular tract | Epididymis, ductus deferens, ampulla | Uterine tube, uterine horn, uterine body |
| Accessory sex glands | Ampulla, vesicular, prostate, bulbourethral | Vestibular glands, cervix |
| Copulatory organ | Penis, retractor penis muscles | Vestibule, vulva, clitoris |
| Key surgical landmark | Vaginal ring, mesorchium | Ovarian pedicle, mesovarium |
| Lymphatic drainage | Inguinal nodes | Iliac and lumbar nodes |

## Development and Descent of the Gonads

The indifferent gonad arises from the urogenital ridge and differentiates under the influence of sex-determining genes. In the male, the testis begins its descent from the sublumbar region through the inguinal canal into the scrotum. The vaginal process, an outpouching of peritoneum, precedes the testis and forms the vaginal tunic. The mesorchium suspends the testis within the vaginal cavity and carries the testicular artery, vein, and ductus deferens. Failure of descent results in cryptorchidism, a condition with both cosmetic and behavioral consequences. The retained testis may lie within the abdomen or within the inguinal canal, and its location determines the surgical approach required for removal. Laparoscopic examination of the abdominal cavity permits identification of the mesorchium and vaginal ring, structures that guide the surgeon to the retained gonad [Laparoscopic anatomy of the equine abdomen](https://pubmed.ncbi.nlm.nih.gov/7785833/).

In the mare, the ovary remains within the abdomen throughout life. It is suspended by the mesovarium from the dorsal body wall, caudal to the kidney. The ovary is bean-shaped and characterized by a distinct depression, the ovulation fossa, which is the only site where ovulation occurs. The ovarian artery and vein course within the mesovarium and are vulnerable to hemorrhage during ovariectomy. The relationship of the ovary to the uterine tube is clinically significant: the infundibulum opens near the ovulation fossa, and the fimbriae partially envelop the ovary at ovulation to capture the released oocyte.

## Stallion Reproductive Tract

### Scrotum, Testis, and Epididymis

The scrotum is positioned high in the inguinal region, between the thighs, and contains two testes separated by a median septum. The testis is ovoid, with its long axis oriented horizontally. The epididymis adheres to the dorsolateral surface of the testis and is divided into head, body, and tail. The tail of the epididymis is palpable per rectum and is the site of sperm storage and maturation. The ductus deferens arises from the tail of the epididymis, courses through the inguinal canal within the spermatic cord, and enters the abdominal cavity through the vaginal ring.

The testicular artery is highly tortuous as it approaches the testis, a feature that facilitates heat exchange and thermoregulation. The pampiniform plexus of veins surrounds the artery and acts as a countercurrent heat exchanger. Disruption of this mechanism, as occurs with fever or scrotal insulation, impairs spermatogenesis. The cremaster muscle and the tunica dartos adjust testicular position in response to ambient temperature.

### Accessory Sex Glands

The stallion possesses four accessory sex glands: the ampullae, vesicular glands, prostate, and bulbourethral glands. The ampullae are dilated terminal portions of the ductus deferentes and contribute a small volume to the ejaculate. The vesicular glands are paired, elongated sacs that lie lateral to the ampullae and secrete a fructose-rich fluid. The prostate surrounds the urethra at the level of the bladder neck and contributes a serous secretion. The bulbourethral glands are small, paired structures located at the pelvic outlet. The combined secretions of these glands form the seminal plasma, which supports sperm survival and modulates the female reproductive tract environment [Seminal fluid and immune adaptation for pregnancy--comparative biology in](https://pubmed.ncbi.nlm.nih.gov/25220746/).

### Penis and Prepuce

The stallion penis is of the musculocavernous type, composed of the paired corpora cavernosa and the corpus spongiosum surrounding the urethra. The glans penis is prominent and expands during erection. The prepuce consists of internal and external folds that retract to expose the penis during urination and copulation. The retractor penis muscles arise from the rectum and insert on the penis, maintaining retraction when not erect. The sigmoid flexure, present in ruminants, is absent in the horse.

## Mare Reproductive Tract

### Ovaries and Uterine Tubes

The equine ovary is unique among domestic species in that the germinal epithelium covers only the ovulation fossa. The remainder of the ovary is covered by tunica albuginea, and the parenchyma is arranged so that follicles and corpora lutea project toward the fossa. This arrangement means that ovulation occurs only at the fossa, and the infundibulum must be positioned accurately to capture the oocyte. The uterine tube is a tortuous tube that runs from the infundibulum to the uterine horn tip. It is divided into infundibulum, ampulla, and isthmus, and it is the site of fertilisation.

### Uterus and Cervix

The equine uterus is a Y-shaped structure with a short body and two long horns. The horns curve dorsally and laterally, and their tips lie near the ovaries. The uterine wall consists of endometrium, myometrium, and serosa. The endometrium contains endometrial cups, which are specialised trophoblast cells that invade the endometrium around day 36 of gestation and produce equine chorionic gonadotropin. The cervix is a thick-walled, muscular sphincter that projects into the vagina. It is normally closed except during estrus, parturition, and certain pathologic states. The cervix is a barrier to ascending infection, and its competence is essential for maintenance of pregnancy.

### Vagina, Vestibule, and Vulva

The vagina extends from the cervix to the external urethral orifice. It is a distensible, muscular tube that accommodates the penis during breeding and the fetus during parturition. The vestibule lies caudal to the urethral orifice and receives the openings of the vestibular glands. The vulva consists of the labia and the clitoris. The clitoris is located in the ventral commissure of the vulva and is homologous to the penis. The vestibular-vaginal junction and the vulvar seal are the primary defenses against ascending infection. The conformation of the vulva, particularly the angle of the vulvar opening relative to the pelvis, influences the risk of pneumovagina and ascending bacterial contamination [Reproductive tract infections in horses](https://pubmed.ncbi.nlm.nih.gov/16882486/).

## Blood Supply and Innervation

The gonads and reproductive tract receive blood from the ovarian, uterine, and vaginal arteries. The ovarian artery arises from the aorta and supplies the ovary and the cranial portion of the uterine horn. The uterine artery arises from the internal iliac artery and supplies the uterine body and horns. The vaginal artery supplies the vagina and vestibule. Venous drainage parallels the arterial supply, with the ovarian vein draining into the caudal vena cava on the right and the renal vein on the left. Lymphatic drainage from the reproductive tract is directed to the iliac and lumbar lymph nodes.

The reproductive tract is innervated by both sympathetic and parasympathetic fibers. The sympathetic supply arises from the lumbar and sacral spinal segments and travels via the hypogastric nerves. The parasympathetic supply arises from the sacral segments and travels via the pelvic nerves. These nerves regulate vascular tone, glandular secretion, and smooth muscle contraction.

## Clinical Examination of the Stallion

A breeding soundness examination begins with signalment, history, and observation of libido and mating behavior. Physical examination should include palpation of the scrotum, testes, epididymides, and spermatic cords. Testicular volume correlates with daily sperm output, and bilateral symmetry is expected. The scrotal skin should be thin and pliable, with the testes oriented vertically. Palpable abnormalities such as firm nodules, heat, or excessive fluid within the vaginal process warrant ultrasonographic assessment.

Rectal palpation and transrectal ultrasonography allow evaluation of the accessory sex glands, the pelvic urethra, and the ampullae. The ampullae are palpable as paired firm cords dorsal to the bladder. The bulbourethral glands are not reliably palpable per rectum. Ultrasonography of the penis and prepuce is reserved for suspected masses, trauma, or neoplasia.

Semen collection with an artificial vagina is the standard method for evaluating ejaculate quality. The stallion should be collected onto a phantom or a live mare in estrus. A breeding phantom with a properly warmed and lubricated artificial vagina minimizes contamination. The ejaculate is evaluated for volume, sperm concentration, total sperm number, progressive motility, and morphology. A second collection one hour after the first is used to assess daily sperm output in stallions with suspected subfertility.

Castration is the most common elective surgery of the male reproductive tract. Open, closed, and semiclosed techniques are described, and the procedure may be performed standing or recumbent. Reported complication rates range from 10.2% to 60%, with most complications being mild. A thorough knowledge of the inguinal canal, the vaginal process, and the relationship of the testicular vessels and ductus deferens is required to avoid hemorrhage, eventration of intestine, or retained testicular tissue. The closed technique, in which the vaginal tunic is not opened, reduces the risk of herniation but requires more dissection. The open technique is faster but exposes the peritoneal cavity to the external environment. The choice of technique depends on patient size, temperament, and surgeon preference.

## Clinical Examination of the Mare

The perineum is examined first. Conformation of the vulva is assessed for vertical orientation, seal, and the angle of the vulvar labia relative to the anus. A mare with a sunken anus and a tilted vulva is predisposed to pneumovagina and ascending contamination. The vestibule and vagina are examined with a sterile gloved hand or a speculum. The vestibulovaginal fold should form a complete seal. The external urethral orifice lies on the floor of the vestibule, and the clitoris lies within the ventral commissure of the vulva.

Transrectal palpation and ultrasonography of the tubular tract are performed in sequence. The cervix is identified as a firm tubular structure between the bladder and the rectum. The uterus is evaluated for symmetry, tone, and the presence of intraluminal fluid. The ovaries are assessed for size, shape, and the presence of follicles or a corpus luteum. Ultrasonography provides real-time information on follicular diameter, endometrial edema, and ovulation. Serial examinations are required to characterize the estrous cycle.

Endometrial cytology and culture are indicated in mares with a history of subfertility, abnormal vulvar discharge, or persistent post-breeding endometritis. A guarded swab or a double-guarded culture instrument is passed through the cervix to minimize contamination from the vestibule and vagina. Cytology is evaluated for the presence of neutrophils. Endometrial biopsy is performed when chronic endometritis, endometrial fibrosis, or uterine neoplasia is suspected. The biopsy is graded histologically, and the grade correlates with the likelihood of carrying a foal to term.

## Reproductive Tract Infections

Reproductive tract infections in the mare are a leading cause of subfertility and early embryonic loss. The most common bacterial isolates include *Streptococcus equi* subspecies *zooepidemicus*, *Escherichia coli*, and *Pseudomonas aeruginosa*. *Taylorella equigenitalis*, the cause of contagious equine metritis, is a notifiable pathogen in many jurisdictions. A diagnosis of venereal disease requires isolation of the organizm from the clitoral fossa, clitoral sinuses, or reproductive tract. The stallion may carry *T. equigenitalis* without clinical signs, and the organizm persists in the urethral fossa and the urethral diverticulum.

Treatment of endometritis is guided by culture and susceptibility testing. Uterine lavage with sterile saline is used to remove inflammatory debris and bacteria. Oxytocin is administered to promote uterine clearance. Mares with delayed uterine clearance have impaired myometrial contractility and may benefit from repeated lavage and ecbolic therapy. The choice of antimicrobial agent depends on the isolate and the route of administration. Systemic therapy is less effective for uterine infections than local infusion, because the equine endometrium does not concentrate systemically administered antimicrobials.

The stallion contributes to the transmission of venereal disease. The penis, prepuce, and urethral fossa should be examined for lesions suggestive of coital exanthema, which is caused by equine herpesvirus type 3. The lesions are vesicular and ulcerative and resolve within two to three weeks. The virus is transmitted by direct contact, and the stallion should not be bred until lesions have healed.

## Laparoscopic Evaluation

Laparoscopy provides a minimally invasive method for evaluating the internal reproductive tract. The procedure is performed with the horse sedated and standing, or under general anesthesia in dorsal recumbency. The abdomen is examined from the left and right paralumbar fossae. In the stallion, the vaginal ring and the mesorchium are visible, and the ductus deferens can be traced from the inguinal region to the pelvic canal. In the mare, the ovaries, uterine horns, and uterine body are visible. Laparoscopy is used to diagnose cryptorchidism, to evaluate the uterus and ovaries in mares with suspected adhesions or neoplasia, and to perform ovariectomy or cryptorchidectomy. The normal laparoscopic anatomy has been described in detail, and the technique is safe when the abdomen is properly insufflated and the portals are placed correctly.

## Mammary Gland Examination

The equine mammary gland is located in the inguinal region and consists of two glands separated by a median septum. Each gland has one teat with two teat canals. The gland undergoes marked postnatal development in association with the reproductive cycle. The epithelial structures are arranged in terminal duct lobular units supported by collagenous stroma. Mastitis is the most frequently described mammary pathology and is most often associated with *Streptococcus* spp. The clinical signs include heat, swelling, pain, and abnormal milk. Mastitis is diagnosed by palpation, ultrasonography, and culture of milk. Mammary tumors are rare and carry a poor prognosis in many cases. The mammary gland should be examined as part of the routine physical examination of the broodmare, particularly in the periparturient period.

| Structure | Function | Clinical Relevance |
| --- | --- | --- |
| Testis | Spermatogenesis and steroidogenesis | Palpate for size, symmetry, and masses |
| Epididymis | Sperm maturation and storage | Palpable along the dorsolateral testis |
| Ampulla | Sperm storage and seminal fluid contribution | Palpable per rectum |
| Bulbourethral glands | Pre-ejaculatory fluid production | Not reliably palpable |
| Ovary | Folliculogenesis, ovulation, progesterone production | Serial ultrasonography for cycle staging |
| Uterine tube | Fertilization and early embryo transport | Not palpable, assessed by inference |
| Uterus | Embryo support, placentation | Evaluate for fluid, tone, and symmetry |
| Cervix | Barrier between uterus and vagina | Must seal during diestrus and pregnancy |
| Vestibulovaginal fold | Physical barrier to ascending contamination | Assess for competence |
| Mammary gland | Lactation | Examine for mastitis and neoplasia |

The correct choice of diagnostic procedure depends on the clinical question. A mare with a history of retained placenta and subsequent endometritis requires culture and cytology before breeding. A stallion with a scrotal hernia requires surgical correction before semen collection. A mare with a suspected granulosa cell tumor requires ultrasonography and hormonal assessment. The evidence base for many reproductive interventions is limited, and the clinician must weigh the cost, risk, and expected benefit of each procedure.

## Recognized Complications and Early Detection

Reproductive tract disease in the stallion and mare often presents with subtle early signs that escalate if missed. In the mare, the most frequently encountered complications include persistent post-breeding endometritis, cervical adhesions or fibrosis, and ovarian hematomas that mimic neoplasia. Endometritis should be suspected when a mare fails to conceive despite apparently normal oestrous cycles, or when ultrasonography reveals intrauterine fluid more than 24 hours after breeding. Cytology and culture of a guarded uterine swab remain the discriminating tests. Cervical damage is detected at speculum examination or during manual palpation per vaginam, a torn or scarred cervix permits air and debris to enter the uterus and perpetuates inflammation. Ovarian hematomas are common after ovulation and appear as enlarging, echogenic masses on ultrasound, serial examinations showing gradual reduction in size over weeks distinguish them from granulosa cell tumors, which persist and are associated with behavioral changes.

In the stallion, the principal complications are post-castration hemorrhage, eventration of omentum or intestine, and infection of the scrotal remnant. Hemorrhage from the testicular artery can be life-threatening and is detected by progressive swelling of the scrotum, tachycardia, and pale mucous membranes in the immediate postoperative period. Eventration is a surgical emergency recognized by omentum or bowel protruding through the scrotal incision. Infection presents with local heat, edema, and purulent discharge within the first week. Early detection relies on owner instruction to monitor the surgical site twice daily and on scheduled re-examination at 24 to 48 hours postoperatively. The reported complication rate for equine castration ranges from 10.2% to 60%, with most events mild, but the serious sequelae demand prompt recognition and intervention.

## Common Errors in Examination and Interpretation

Less experienced clinicians frequently mistake the normal equine ovary for a pathological structure. The equine ovary has a central ovulation fossa and a cortex that is inverted relative to other domestic species, so the palpable and ultrasonographic appearance is dominated by stroma and large follicles. A firm, rounded ovary in dioestrus is often a corpus luteum, not a tumor. The corrective action is to re-examine the mare at a different stage of the cycle before concluding that a mass is abnormal.

A second recurring error is the failure to distinguish the clitoral sinuses from the urethral orifice during endoscopic or speculum examination of the vestibule. The clitoral fossa may harbour the venereal organizm *Taylorella equigenitalis* in carrier mares, and sampling the wrong site yields false-negative cultures. The discriminating check is anatomical: the urethral orifice lies on the floor of the vestibule cranial to the clitoris, and the clitoral sinuses are within the glans itself.

In the stallion, the most common interpretive error is the diagnosis of cryptorchidism in a gelding that has actually undergone incomplete castration with retention of the epididymis or a portion of the tail of the epididymis. These animals show stallion-like behavior but have no testicular tissue. Measurement of anti-Müllerian hormone or human chorionic gonadotrophin stimulation testing discriminates between the two conditions. A second error is the assumption that a unilaterally cryptorchid stallion is sterile, fertility is often preserved, and the retained testis must be located surgically or laparoscopically. Laparoscopic evaluation provides reliable identification of the internal genitalia and is particularly useful when the testis is abdominal.

## Limitations of the Evidence and Areas of Disagreement

The evidence base for equine reproductive anatomy and its clinical application is uneven. Much of the descriptive anatomy is well established, but the pathophysiology of several common conditions remains contested. The role of seminal plasma in priming the mare's uterine immune response is supported by comparative studies across species, yet the clinical relevance in the horse is still debated. Some authors advocate routine uterine lavage after breeding in susceptible mares, while others reserve it for mares with documented fluid accumulation. Neither position is supported by large prospective trials.

The immunology of pregnancy in the mare is better characterized than in many species because the invasive trophoblast can be recovered non-surgically, but the translation of these findings to clinical pregnancy loss is incomplete. Expert opinion also differs on the management of the retained testis in cryptorchid horses, particularly on whether laparoscopic removal or open inguinal approaches carry lower morbidity. The choice depends on surgeon experience and available equipment.

## Referral, Laboratory Involvement, and Regulatory Reporting

Referral to a specialist is warranted when a mare fails to conceive after three or more breeding cycles with apparently normal findings, when cervical or uterine adhesions require surgical correction, or when an ovarian mass cannot be characterized by serial ultrasonography. Stallions with ejaculatory dysfunction, penile trauma, or suspected testicular neoplasia should be referred for andrological evaluation and, where indicated, semen collection and assessment.

Laboratory involvement is required for bacterial and fungal culture of uterine swabs, venereal disease screening, hormonal assays, and histopathology of excised tissues. The clitoral sinus and urethral swabs of breeding stallions and mares should be cultured for *Taylorella equigenitalis* in accordance with regional requirements. Regulatory reporting obligations vary by jurisdiction, but contagious equine metritis, equine viral arteritis, and dourine are notifiable in many countries. Clinicians must consult the relevant national authority and the [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) for current disease notification requirements. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific guidance on the diagnosis and management of reproductive tract infections.

| Observation | Likely Cause | Discriminating Check |
|---|---|---|
| Intrauterine fluid after breeding | Endometritis, poor lymphatic drainage | Uterine cytology and culture, serial ultrasound |
| Enlarging ovarian mass | Hematoma vs granulosa cell tumor | Serial ultrasound over 3 to 4 weeks, hormone panel |
| Stallion-like behavior in a gelding | Incomplete castration vs cryptorchidism | Anti-Müllerian hormone assay or hCG stimulation test |
| Scrotal swelling after castration | Hemorrhage vs infection vs eventration | Physical examination, ultrasound, immediate surgical exploration if progressive |
| Clitoral culture negative in a suspect carrier | Sampling error | Sample the clitoral sinuses specifically, not the vestibular floor |

## Frequently Asked Questions

### How Should I Adapt a Breeding Soundness Examination When Only Basic Restraint and Minimal Equipment Are Available?

A complete examination requires an endoscope, ultrasound, and culture media, but a useful field assessment is still possible. For the stallion, manual palpation of the scrotum, testis, and epididymis, visual inspection of the penis and prepuce, and collection of an ejaculate into a warmed, filtered receptacle allow gross evaluation of volume, color, and motility. For the mare, transrectal palpation of the ovaries, uterus, and cervix can be performed without ultrasound, though it is less sensitive for early pregnancy and endometrial pathology. Record what was assessed and what was not, and state clearly in the record that the examination was limited. Refer cases requiring endoscopic or ultrasonographic evaluation to a hospital setting. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides protocols for field-based reproductive assessment.

### What Are the Minimum Record-Keeping Requirements for Breeding and Reproductive Procedures?

Records should document the identity of the animal, the date, the procedure performed, the person responsible, and any findings or complications. For breeding management, record oestrous cycle stage, breeding dates, the stallion used, and pregnancy diagnosis results. For surgical procedures such as castration, record the technique, anesthetic approach, and postoperative instructions, as complication rates vary with technique and aftercare [complications of equine castration](https://pubmed.ncbi.nlm.nih.gov/34116922/). If reproductive tract infections are diagnosed, document the pathogen, antimicrobial selection, and treatment duration. Regulatory reporting obligations differ by jurisdiction and by the pathogen involved, so consult the [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) and local authorities before proceeding.

### How Does the Approach to Reproductive Anatomy Differ When Examining a Donkey or a Mule?

The general anatomical plan is shared across equids, but size and proportions differ. Donkeys have smaller testes relative to body size, a longer and more pendulous penis, and a narrower pelvic canal in the mare. Mules are usually sterile, and the gonads may be smaller than expected for the body size. The cervix of the jenny is longer and more tortuous than that of the mare, which makes transcervical procedures more difficult. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) notes that reproductive management protocols developed for horses require adjustment for these anatomical differences. When in doubt, use ultrasound to confirm ovarian and uterine dimensions before proceeding with artificial insemination or embryo transfer.

### What Should I Tell a Client When a Stallion Fails to Achieve an Erection or Ejaculation During Collection?

Explain that collection failure is common on the first attempt and does not by itself indicate infertility. Outline the possible causes: environmental distraction, inadequate stimulation, pain from the back or limbs, or a learned aversion. Recommend a quiet collection area, a reliable teaser mare, and a consistent routine. If failure persists across multiple attempts, schedule a full examination including testicular palpation, ultrasound of the accessory glands, and hematology. The [reproductive tract infection review](https://pubmed.ncbi.nlm.nih.gov/16882486/) emphasizes that infection and inflammation can reduce libido and ejaculatory function, so do not assume a behavioral cause without ruling out physical disease.

### How Do I Explain the Importance of the Equine Mammary Gland Examination to a Client Who Sees It as Unnecessary?

Frame the examination as part of routine reproductive health monitoring, not as an optional extra. The equine mammary gland undergoes substantial postnatal development in association with the reproductive cycle, and pathology can present with subtle signs that overlap between mastitis and neoplasia [development and pathology of the equine mammary gland](https://pubmed.ncbi.nlm.nih.gov/33280071/). In a non-pregnant mare, unexpected lactation or asymmetry warrants investigation. In a postpartum mare, mastitis can reduce milk quality and compromise foal health. A brief visual inspection and palpation of all four quarters takes less than a minute and provides a baseline for future comparison. Emphasize that early detection of a mammary mass carries prognostic value because equine mammary tumors are rare but often aggressive.

### When Should I Refer a Mare or Stallion for Advanced Imaging or Surgery instead of Continuing With Medical Management?

Refer when the diagnostic question exceeds the capability of your equipment or when a condition fails to respond to appropriate medical therapy. For the mare, persistent endometritis despite culture-guided treatment, suspected uterine adhesions, or an ovarian mass of uncertain character warrants ultrasound, biopsy, or laparoscopy. Laparoscopic evaluation provides direct visualization of the reproductive tract and is particularly useful when transrectal palpation and ultrasound are inconclusive [laparoscopic anatomy of the equine abdomen](https://pubmed.ncbi.nlm.nih.gov/7785833/). For the stallion, refer for ultrasonography of the accessory glands, endoscopic examination of the urethra, or surgery when testicular neoplasia, inguinal hernia, or severe penile trauma is suspected. Discuss the financial implications with the client before referral so that the diagnostic plan matches the resources available.

## Related Clinical & Scientific Guides

* [Canine Respiratory System: Anatomy and Physiology](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/canine-respiratory-system-anatomy-physiology)
* [Comparative Anatomy of the Mammalian Kidney](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/comparative-anatomy-mammalian-kidney)
* [Feline Cardiopulmonary Physiology: Heart-Lung Interactions](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/feline-cardiopulmonary-physiology-heart-lung-interactions)


## References and Further Reading

- [Maternal immune responses to trophoblast: the contribution of the horse to pregnancy immunology.](https://pubmed.ncbi.nlm.nih.gov/20618178/). 2010.
- [Reproductive tract infections in horses.](https://pubmed.ncbi.nlm.nih.gov/16882486/). 2006.
- [Laparoscopic anatomy of the equine abdomen.](https://pubmed.ncbi.nlm.nih.gov/7785833/). 1995.
- [Castration Complications: A Review of Castration Techniques and How to Manage Complications.](https://pubmed.ncbi.nlm.nih.gov/34116922/). 2021.
- [Development and Pathology of the Equine Mammary Gland.](https://pubmed.ncbi.nlm.nih.gov/33280071/). 2021.
- [Seminal fluid and immune adaptation for pregnancy--comparative biology in mammalian species.](https://pubmed.ncbi.nlm.nih.gov/25220746/). 2014.
- [NCBI Bookshelf: Veterinary and Comparative Biomedical Sciences](https://www.ncbi.nlm.nih.gov/books/). NCBI Bookshelf.
- [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.

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> 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.