Clinical exam of the Mare

  • It may be obvious but identification of the mare should be established, especially in cases where sale or purchase is involved. Microchip or tattoo is preferred.
  • A thorough history is essential in a reproductive exam of a mare. It is important to consider the overall status of the mare.
  • What is her age? Young mares, such as 2-3 yr olds are more likely to have abnormal cycles. Old maiden mares may be more difficult to get in foal.
  • What has been her immediate past use? Hormone administration associated with athletic performance (i.e. racing) may have a detrimental effect on fertility, at least short term.
  • What is her reproductive status? Is she a maiden, barren, or foaling mare?
  • Consider the stallion that is being used or will be used -natural or AI breeding, fresh, fresh cooled or frozen semen? Is he fertile? Obtain the year by year reproductive history.
  • Have there been previous pregnancies and what was their outcome? Consider anatomic changes associated with multiple foalings.
  • Has the mare ever aborted? Is there any record of twinning? Has she ever had dystocia? Has she ever has early embryonic death?
  • Is there any record of postpartum complications such as retained placenta or metritis? Has she ever had previous reproductive surgery?
  • What are the management conditions? What sort of teasing program is used? How is breeding managed and what sort of treatments have been used? Is lighting used to hasten cyclicity? Has she ever had abnormal cyclic patterns?
Physical Exam
  • The physical exam should begin with an assessment of the mare's general condition, for example a long winter haircoat persisting into spring may be associated with anestrus.
  • Examine the external genitalia and perineum. 
    • Is there any discharge? 
    • How is the vulvar conformation? 
    • The vulva should be perpendicular to the ground with >70% of the vulva below the ischium.
    • The labia should form a good seal and close completely.
    •  The "windsucker" test, performed by parting the vulvar labia and listening for an inrush of air, tests the integrity of the vaginal vestibular sphincter.  Older, thin mares with a flat croup and atrophy of vulvar lips are more prone to pneumovagina.
  • The vaginal vestibular sphincter is the most important of the barriers to contamination of the reproductive tract. (The others are the labia and the cervix.) 

Examination of the conformation of the labia.

Locating the pelvic brim (left) and performing a 'windsucker test' (right).

Rectal Palpation

  • The rectal exam is usually the next step. Proper restraint is important.
  • Students are usually concerned about rectal tears. 
    • The risk can be reduced to some degree if proper restraint is used, adequate lubrication is used and with proper manual technique. 
    • Just as important is knowing what to do if one occurs. 
      • If a tear occurs or is suspected, examine the tear (by speculum and manually) immediately. 
      • Inform the owner what has happened. 
      • Determine if it is a Grade 1,2,3 or 4. 
      • Treatment depends on the grade of tear, economics, client, etc. 
        • Grade 1 tears (mucosa only) may not need much treatment, maybe broad spectrum antibiotics and observation. 
        • Grade 2 tears (muscularis only) may go unnoticed. 
        • Grade 3 tears (everything but the serosa) are more serious and require treatment. 
          • The aim is to prevent a grade 3 from becoming a grade 4. 
          • Initial treatment should consist of broad spectrum antibiotics, tetanus, anti-inflammatories, stool softening, anti-peristaltics (if available) and packing the tear with medicated gauze. 
          • Many, if not most of theses cases will go to surgery. 
          • Others may be treated medically, just by replacing the packing periodically and maintaining the antibiotics and stool softeners. 
        • Grade 4 tears (all layers -full thickness) either go to surgery immediately or are euthanized.
  • The exam should be complete and systematic.
  • The cervix reflects the presence of progesterone. 
    • If progesterone is high, such as in pregnancy or dioestrus, it is long, firm and tubular. 
    • When progesterone is low, such as in estrus or anestrus, it becomes softer, flatter and shorter. 
    • In fact, when a mare is near ovulation, it is very short, soft, and may be difficult to discern
  • The uterus should be examined next. 
    • Always check for pregnancy first! 
    • When examining the uterus, estimate the size of the uterine horns and the tone. 
    • The tone of the uterus follows the cervix. 
      • During estrus it is softer, with less tone, during diestrus it has increased tone and a more tubular feel, during anestrus it is thin, flaccid, and often difficult to palpate. 
    • The uterus should be examined for contents (i.e. pregnancy, fluid) and consistency, such as ventral enlargements at the junction of the horn and body, atrophy, fluid, endometrial cysts (a common occurrence but often not palpable), or a doughy, thick walled uterus (may indicate lymphatic lacunae). Deep palpation of the endometrial folds may reveal areas devoid of folds.
  • After the uterus, palpate the ovaries. 
    • Evaluate the size (keeping in mind seasonal effects), activity, structures present and their size and softness. 
    • Follicles increase in size and become softer as they near ovulation. I
    • t is also helpful to record the location (e.g. AP - anterior pole, PP - posterior pole, etc.) of follicles. 
    • Corpora hemorrhagica (CH) can be palpated as well. Initially following ovulation, a depression is felt. 
    • The mare may show pain on palpation of a fresh ovulation. 
    • By 24 h after ovulation, the hemorrhage into cavity forms a clot which may re-distend the structure.
    • By 2 or 3 d following ovulation, a CH and a follicle may feel similar, in which case you may need to rely on behavioral signs and the cervix to distinguish between the two. 
    • The mature (>5 d) CL cannot be palpated due to retraction into the ovarian stroma.

Ultrasound exam
  • A key feature of the reproductive exam is the ultrasound exam. With the ultrasound, you are able to see much more than you can feel.
  • Basically, the lower the MHz, the farther the image penetrates but finer detail is lost; the higher the MHz, the image penetrates less deeply but more detail is seen. With the ultrasound, not only can ovarian structures be seen and easily measured, but their shape and echogenicity can also be evaluated.
  • Follicles not only increase in size as they near ovulation but change shape, becoming more pear-shaped as they develop a tract toward the ovulation fossa.
  • An immature CL can easily be distinguished from a follicle.
  • A CL can be identified with ultrasound even though it cannot be palpated.
  • Anovulatory follicles can be identified.
  • Granulosa cell tumors can be differentiated from hematomas.
  • Uterine size can be measured. Any contents can be identified. Even small amounts of fluid can be identified as well the amount of fluid measured and the character evaluated.
  • Edema of the uterus is characteristic of estrus and is easily recognized, endometrial cysts can not only be identified but their size and location recorded for future reference.
  • In short, an ultrasound examination is critical in the evaluation of a mare and breeding management.

Equine Reproductive Ultrasonography: An Overview

  • Ultrasonography has become an indispensable part of stud farm practice. 
  • Ultrasonography is used for diagnosis and management in almost every aspect of breeding management. 
  • In this overview of equine reproductive ultrasonography, the organs examined, reasons for examination and some possible findings will be briefly reviewed. 
  • More detailed information will be provided in the lectures, discussions and laboratory sessions.


  • Examination of the ovaries can aid in determining the stage of the cycle and in predicting or identifying impending ovulation.
    Characteristics of the ovaries at the various stages of the estrous cycle are:
    • Anestrus: small ovaries, absence of a corpus luteum (CL), no follicles > 20 mm
    • Transition: ovaries of variable size, absence of a CL, follicles > 25 mm present
    • Estrus: ovaries of variable size, absence of an active CL, may see regressed CL, follicles > 25 mm present, usually 1, occasionally 2, large (dominant) follicle present
    • Luteal (Diestrus): early - evidence of recent ovulation; later - ovaries of variable size, follicles may be present and can be large, CL present



  • Various parameters have been investigated in an attempt to predict with accuracy the time of ovulation. The importance of predicting ovulation with accuracy increases with the use of shipped semen and becomes critical when breeding with frozen semen. By palpation, the estimation of follicular size and softness are the parameters used. With experience, competency can be developed but there remains an element of subjectivity and errors will occur with even the most experienced palpators. For these reasons, objective criteria using ultrasonography have been sought after. Unfortunately, at this time, no single reliable criteria has been found which answers the need. Using a combination of criteria will aid somewhat in the accuracy of prediction.
  • Increase in follicular size: Generally, follicles will increase in diameter as they mature and approach ovulation. However, rate of growth and maximum diameter reached will vary somewhat with season and between mares. Maximum diameter will be slightly smaller near the summer solstice. When measuring follicles, differences of 1 or 2 mm can be found just by measuring slightly different points on the follicle on an image, measuring different images of the same follicle or with 2 different operators. Therefore, general trends are probably more beneficial than absolute measurements.
  • Change in follicular shape:
    • Ginther reported that follicles will frequently develop a "pear-shaped" appearance shortly before ovulation. The "stem" of the pear is the tract the follicle develops leading to the ovulation fossa. This characteristic shape is quite variable and depends on obtaining the right angle with the ultrasound probe. That is, if you slice a pear lengthwise through the base to the stem, it will have a "pear-shape" but if you slice it at a right angle to that, it will have a spherical shape. Likewise, the probe must be positioned properly to get the "right slice". Moreover, not all follicles can be seen to develop this shape leading up to ovulation.

    • Follicles initially appear nearly spherical. As they mature, the follicle wall becomes thinner and hence the follicular shape is more easily changed. For this reason, the shape of the follicle may appear more elliptical or irregular as it matures and nears ovulation. The wall of the follicles may appear less smooth as well. In other cases, the follicle will maintain a spherical appearance until ovulation.

  • Echogenicity of antrum: Reports vary on the appearance of echogenic particles before ovulation. In many cases, hyperechoic particles will appear in the antrum close to ovulation. However, if these particles increase in number and echogenicity, this indicates that the follicle is likely to be anovulatory.

  • It is important to be able to recognize ovulation. This is a key event in the management of endometritis, scheduling pregnancy examinations, etc. Because mares remain in estrus behaviorally after ovulation, many mares are bred needlessly after they have ovulated. Detecting ovulation will reduce unnecessary breedings, thereby reducing contamination of the uterus and preserving stallion reserves for mares that need it.
  • Article - to find out more click here.

Corpus luteum

  • A very recent ovulation may be hard to detect upon examination. 
  • Within 12 - 24 hrs, it will fill in and have a hyperechoic appearance. 
  • The equine CL has great variation in its ultrasonographic appearance. 
  • It can have a homogenous echotexture or a trabecular appearance. 
  • The appearance often changes somewhat as the CL matures. A CL may remain visible as a smaller hyperechoic structure even after luteolysis.

Ovarian abnormalities

The section on ovarian abnormalities covers this area in more detail.


  • Examination of the uterus is extremely helpful in determining the stage of the estrous cycle.
    • Anestrus: the uterus is thin and elliptical, with a fairly homogenous echotexture, bright spots indicating air are not uncommon
    • Estrus: a characteristic pattern, giving the appearance of an orange slice or wagon wheel, results due to the edema in the endometrial folds

    • Diestrus: edema is absent, the uterus is round (more so than during anestrus), homogenous echotexture of the uterus
  • This is helpful when breeding a mare with shipped semen. For example, if a mare is given prostaglandin and is presented for examination based on the time lapse since the prostaglandin injection and the owner's impression that the mare is coming into estrus, and upon examination has a 43 mm follicle but no edema in the uterus - should semen be ordered? Probably not. It may be that that follicle is going to regress and she will build a new follicle, accompanied by uterine edema, in the next few days.


Uterine pathology

  • The ability to view uterine pathology with ultrasonography is indispensable in managing the infertile mare. 
  • Excessive uterine edema and fluid in the lumen during estrus before breeding, retention of fluid in the uterus after breeding, fluid in the uterus during diestrus are all examples of pathologic problems that would go undiagnosed without the benefit of ultrasound. 
  • As our understanding of endometritis has developed the underlying importance of uterine clearance mechanisms is felt to be central to the problem of post breeding endometritis. 
  • The best way to diagnose this problem is with ultrasonography in the period after mating. 
  • Fluid present in the uterus at 12 or 24 hours after breeding is a clear indication for therapy to improve uterine clearance.

  • Endometrial cysts, although their role in infertility is somewhat controversial, may cause problems in early pregnancy diagnosis and identification of twins. 
    • During ultrasound examinations before breeding, the location, size and shape of endometrial cysts should be recorded. 
    • Photographic records are ideal. 
    • In this way, archival information is available which will aid in future examinations and the ability to discern a vesicle.



  • Early detection of pregnancy is critical for good broodmare management. 
  • The reasons for early detection are discussed more thoroughly in the chapter on "Twinning in Mares". 
  • Basically, it not only provides information on whether or not the mare is pregnant but allows one to manage twin pregnancy in the most advantageous manner, may serve to give early notice of a uterine infection and if not pregnant allows mare time to arrange re-breeding.
  • Normal development of the pregnancy can be monitored and it is advisable for the practitioner to be familiar with the normal appearance of the conceptus. For example, inexperienced users can sometimes mistake a single conceptus with a developing allantois for twins. Knowledge of the normal appearance and size of a conceptus may indicate an abnormality which is likely to lead to early embryonic death.
  • Fetal sexing can be performed at approximately 60-70 d by the transrectal route and after approximately 100 d by transabdominal approach. 

Assisted Reproduction Techniques

  • Ultrasonography has opened up new possibilities for assisted reproduction in horses. 
  • Oocyte collection for GIFT and IVF is based on ultrasound guided transvaginal oocyte aspiration. 

Vaginoscopic exam

  • The next step is usually a vaginoscopic exam.
  • The mare's cervix changes during the cycle. 
    • It is pink (estrogen enhances the blood supply), edematous, relaxed (lying on the vaginal floor near ovulation), and moist during estrus; 
    •  pale, dry, and closed (projecting out from the middle of the anterior vagina during diestrus), often referred to as "high, white, and tight". 
    • During pregnancy, it is pale, tightly closed and covered with a sticky blue-gray mucus. During anestrus it is very pale, flaccid, and may be open allowing you to see into the uterus.

Vaginal exam during estrus (left) and diestrus (right).
  • Abnormal findings on vaginoscopic exam include pneumovagina, where you may see the presence of debris or froth in the anterior vagina and slight hyperemia; urine pooling which is usually most evident during late estrus and is not uncommon at foal heat; vaginitis or cervicitis; adhesions, scars, or lacerations; a persistent hymen; exudates; and varicose veins.

Urine Pooling and a vaginal adhesion.

  • The vaginoscopic exam may be followed by direct palpation of the vagina, cervix and endometrium. You will be unable to completely evaluate the cervix with a speculum and direct palpation of the cervix is important to evaluate it for adhesions, lacerations, etc. as well as the normal changes during the cycle. This is usually performed at the same time as obtaining the culture and cytology specimen. Direct palpation of the endometrium is not routinely performed, especially since the advent of ultrasound.
Fiberoptic exam of the uterus, although not a part of the routine examination, should be considered in problem mares or when indicated by the history.

Folds of the uterus inflating (left and center) and the oviductal papilla (right) where the oviduct enters the uterus.

Diagnostic procedures
Culture & cytology
  • Culture & cytology of the uterus should be considered as a single procedure.
  • A culture without an accompanying cytology is worthless because it is impossible to distinguish a contaminant from a pathogen.
  • The best time to perform the procedure is during (late) estrus.
  • It is absolutely essential that the swab used is a guarded swab. An alternative to using a swab is a low volume flush.
Top to bottom: Kalayjian, Accu-CulShure, Tiegland.

Left to right : unguarded , guarded, guarded.

Transport mechanisms.


The culture/cytology system from Mini Tube that we use.

From top - Cytology brush with passer, Culture tip with passer, Guarded Introducer, Introducer with passer (end you hold)

  • While studies have shown no difference for normal mares, in subfertile mares there were fewer positive cultures and fewer positive cytologies with a swab than with a flush.
  • Culture results must be correlated with cytology findings and pathogens differentiated from non-pathogens.
  • A positive culture with a negative cytology should be disregarded as a contaminant. A positive culture with a positive cytology should be interpreted as isolation of a pathogen and sensitivity performed.
  • A negative culture and positive cytology may indicate noninfectious inflammation or a problem with sample handling.

Low volume flush cultures

  • Recent work (as well as some older work) has shown this may be more sensitive at diagnosing mares with uterine infections.
  • Insert a Bivona catheter through the cervix (do not inflate the cuff)
  • Flush 60 mL of saline into the uterus using a catheter tip syringe and retrieve after 30 second uterine message per rectum into drained into a sterile 50 mL conical tube3 by gravity flow.
  • An aliquot (4 mL) of the sample was placed in a 5 mL sterile tube for measuring pH.
  • centrifuge remaining sample at 500 rpm for 10 min. and decant all but 5 mL of the supernatant
  • Insert a sterile culture swab into the pellet for subsequent microbiologic culture.
  • Use a second sterile swab rolled onto a glass slide  for cytological examination.

Biopsy Cultures

  • Some prefer to culture the biopsy
  • Strep can be present deep in tissue and not on surface


Endometrial biopsy

Obtaining a biopsy. Pass the biopsy instrument manually through the cervix, pull your hand out and place your hand in the rectum, push a fold of endometrium into the jaws, close the jaws and tear out the biopsy sample.

  • The endometrial biopsy is usually the last step in the breeding soundness examination. It is indicated in prepurchase exams, barren mares and mares requiring reproductive surgery, among others.
  • When to perform a biopsy is a matter of choice and availability. 
    • During estrus the cervix is open and more easily penetrated and the mare is more resistant to endometritis, while during diestrus the endometrial glands are more active and may give a better picture of their function.
  • Early work indicated that one site was representative, however we now know that there may be significant differences between sites in a uterus. Therefore, in deciding where to obtain the biopsy, if palpation or ultrasound indicates an abnormal area, biopsy that area as well as a normal area. Otherwise, choose a site at random, being sure to stay away from the cervix and area near the internal os.
  • To be able to interpret the biopsy, it is important to obtain an adequate sample.
    • Modified Davidson's solution may be better the formalin or Bouin's to fix the sample.
      • (30% of a 37-40% solution of formaldehyde, 15% ethanol, 5% glacial acetic acid, and 50% distilled H2O)
Adequate biopsy size.
  • The biopsy is examined for signs of inflammation. 
    • Neutrophils will be present in the acute stage while lymphocytes and macrophages are seen in chronic inflammation. 
    • Eosinophils are associated with fungal infections or pneumovagina. 
  • In addition, the biopsy is evaluated for the degree of fibrosis (absent, mild, moderate, severe) based on the number of layers and the frequency of lesions (how widespread).
Fibrosis and nesting
  • Glandular nests are recorded, and whether fibrotic or physiologic. 
    • Physiologic nests occur during anestrus and transition and can be differentiated by the absence of layers of fibrosis around the glands. 
    • Periglandular fibrosis around individual glands is evaluated as well (scattered, widespread, frequent, occasional, number of layers).
Fibrosis around glands.
Other evaluations
  • The endometrial epithelium is evaluated and the tortuosity of glands (more tortuous under the influence of progesterone). Any indications of endometrial atrophy are noted. Endometrial atrophy is considered abnormal during breeding season and may be localized in older mares. Cystic (dilated) glands are noted. These are nonfibrosed glands distended with inspissated secretions and are common during anestrus and transition.
  • Siderocytes are an indication of previous pregnancies.
  • Lymphatic lacunae are evidence of abnormalities in lymphatic drainage and are important factors in infertility. The pattern of lesions is noted. Widespread lesions are numerous and appear widely throughout the sections. Scattered lesions are few and irregularly distributed. Discrete foci are concentrated changes with rather sharp, well-defined margins. Diffuse foci are spread out with indefinite margins.
  • The biopsy is assigned to a category based on the evaluation.
  • The categories are: I - essentially normal, pathologic changes slight and sparsely scattered; IIA - mild changes; IIB - moderate changes; III - severe changes.
  • The effects are additive and if a mare is barren > 2 yr the score is increased one grade. More information on criteria for evaluating a biopsy and placing it into a category can be found in the chapter by Kenny and Doig in Current Therapy in Theriogenology II. The categories have been associated with the expected foaling rate.
  • Category I mares have an expected foaling rate of 80-90% and the foaling rate reflects the overall management.

A grade I biopsy.

  • Category IIA mares have an expected foaling rate of 50-80% and the foaling rate reflects overall management plus endometrial changes.
  • Category IIB mares have an expected foaling rate of 10-50% and again the foaling rate reflects overall management plus endometrial changes.
  • Category III mares have an expected foaling rate of 10% and the foaling rate reflects severe changes in the endometrium.

contributed by Bruce E Eilts and modified on 8 September 2009

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contributed by Bruce E Eilts on 25 September 2012


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