Breeding Soundness Examination of the Mare

The breeding soundness examination (BSE) of the mare is a complete reproductive exam that should be performed by an experienced equine veterinarian in a systematic, accurate and thorough manner. The complete BSE should always include the following procedures:

  • Accurate identification of the mare
  • Recording of the mare's breeding and foaling history
  • Physical examination and evaluation of the perineal (vulvar) conformation
  • Palpation and ultrasonography of the reproductive tract
  • Endometrial (uterine) swab for microbial culture
  • Speculum exam of the vagina and cervix, and digital exam of the cervix
  • Biopsy sample of the endometrium (lining of the uterus)

    Reasons to perform this exam include:

  • Barrenness or history of infertility
  • Pre-purchase examination
  • History of previous foaling complications or injuries
  • Recent abortion

    Additionally, a BSE should be performed in mares whose owners plan to invest in expensive assisted reproductive procedures, such as embryo transfer, or in mares to be bred with expensive transported (cooled) or frozen/thawed semen. A complete BSE need not be performed routinely in maiden mares entering a breeding program, unless pre-breeding palpation or ultrasound exam of the uterus reveals an obvious abnormality.

    The BSE is NOT a test for fertility, but only a thorough exam that will allows speculation of the likelihood for a mare to become pregnant and/or carry a foal to term. The only true test for fertility is to breed a mare under good reproductive management conditions to a fertile stallion, and monitor if she becomes pregnant and delivers a healthy foal 11 months later.

    Breeding Soundness Exams

    A breeding soundness examination (BSE) should never be performed in a mare that cannot be accurately identified by branding, lip tattoos or breed registration records.

    The breeding and foaling history should be carefully recorded since it is an essential tool to help ascertain if or why a mare is having fertility problems:

  • Well recorded teasing and breeding records may allow us to determine whether breeding management was appropriate. One should keep in mind that poor breeding management, such as breeding mares at the wrong time during their cycle and/or with poor quality semen, is probably the most common cause of infertility.
  • Young maiden mares (mares never bred before) should not require a complete BSE before entering a breeding program, unless an obvious abnormality is detected during routine examination prior to breeding. Bridging the vagina and/or uterus in an otherwise seemingly normal mare will not yield any valuable information and may induce a uterine infection.
  • A different situation occurs when purchasing an old maiden mare (>15 years) for breeding purposes only, in which case the BSE may yield important information regarding the health of the endometrium (uterine lining) and hence the chances for the mare to carry a foal to term. Typically, it can be expected that older mares will have some degree of subfertility; this is either manifested by low pregnancy rates or by increased frequency of pregnancy loss (miscarriage). These mares often have problems such as air sucking or urine pooling in the vagina due to poor perineal conformation and loss of tone (sagging) of the reproductive tract. Additionally, old mares will have aged oocytes (eggs), less suitable of becoming properly fertilized or of developing into a normal fetus.
  • A barren mare that has been bred but that has never become pregnant, may have a congenital (from birth) abnormality of the reproductive tract such as hypoplastic (small) ovaries, abnormal development of the uterus or hydrosalpinx (blockage of the Fallopian tubes or oviducts). In mares with congenital anomalies, a sample of blood and/or skin should be sent to the laboratory for karyotyping, or chromosomal analysis.
  • A barren mare that was bred last season but is not going to deliver a foal this season, although she has produced a foal sometime in the past, may have a uterine infection (endometritis) or degenerative changes of the endometrium (i.e. uterine lining). A history of dystocia (difficult foaling) should prompt the veterinarian to check for cervical, vaginal and perineal (vulvar) scars or tears.

    Physical Examination and Perineal (Vulvar) Conformation Evaluation

    The mare breeding soundness examination (BSE) should always include a complete physical exam. Undernourished and obese mares may have problems becoming pregnant, carrying to term or foaling. Mares with physical problems, especially those causing severe pain such as laminitis (founder) usually have cyclicity problems and seldom become pregnant. Endocrine diseases, such as Cushing's, may affect reproductive cyclicity or predispose breeding mares to uterine infections.

    Perineal conformation evaluation is especially important in older mares. A competent, tightly closed and properly shaped vulva will protect the reproductive tract from ascending infections. In older and undernourished mares, lack of muscle tone and fat around the perineal area may result in the upper part of the vulva being sunken forward, instead of perpendicular to the ground. This defect predisposes to problems such as fecal contamination of the vestibule or vagina, air sucking and urine pooling. Poor vulvar conformation may also be linked to incompetence of the vestibulo-vaginal sphincter (ring of tissue that separates the vestibule from the vagina), predisposing these mares to vaginal or uterine infections. Such problems can be corrected with relatively simple surgical procedures suited for each specific defect.

    While evaluating the mare's external genitalia it is also important to note any discharges coming through the vulvar lips that may be an indication of a reproductive tract infection.

    Palpation and Ultrasonography of the Reproductive Tract

    The ovaries and uterus of the mare are examined by palpation and ultrasound through the rectal wall, since the reproductive tract (ovaries, uterus, cervix and vagina) is located in the pelvic cavity just below the rectum. For this purpose, the mare should be restrained in stocks or held with her rear end against the opening of a stall door. A nose twitch or sedative may be used if deemed necessary to minimize risks of injury for both the veterinarian and the mare. The veterinarian's arm is suited with a well-lubricated disposable plastic sleeve and inserted into the rectum of the mare. Feces must be carefully removed from the mare's rectum prior to the exam.

    Palpation (feeling) of the mare's ovaries allows the veterinarian to ascertain their shape and relative size. Palpation of both the ovaries and uterus can help the veterinarian estimate the stage of the estrus cycle, based follicular activity and the tonicity (hardness) and shape of the uterus and cervix. Abnormalities such as missing parts or masses (swellings) can be detected with this technique.

    Ultrasonography is a much more sensitive technique to detect some changes of the reproductive tract such as uterine edema, cysts or fluid within the uterus:

  • Edema (fluid within the uterine wall), which gives the uterus a pinwheel or sliced orange appearance, is normally seen in mares in heat, but can otherwise be a sign of uterine inflammation and infection.
  • Cysts are fluid filled lymphatic swellings within the uterus that do not usually interfere with the mare's ability to conceive or carry to term. Only when extremely large or present in large numbers, do cysts interfere with the mare's ability to support the early embryo and predispose the mare to embryonic loss. Round small cysts can be easily confused with an early pregnancy (embryo) and thus should be carefully recorded when detected.
  • A small amount of fluid within the uterus may be a normal finding when mares are in heat. Large amounts of fluid or any amount of fluid in a mare that is not in heat is an abnormal finding usually consistent with endometritis (uterine infection). One should carefully interpret this finding together with the results of culture and biopsy to decide on the cause and course of treatment.

    Endometrial (Uterine) Culture and Biopsy and Other Specific Procedures

    Before bridging the reproductive tract (penetrating the cervix and entering the uterus) to obtain samples for culture and biopsy, two important objectives must be accomplished:

  • If there is any chance at all that the mare might have been bred, the veterinarian must make sure that she is not pregnant at the time of the exam, which is done through palpation and ultrasound exam of the uterus. Going through the cervix to take a culture or biopsy sample in a pregnant mare will induce pregnancy loss or abortion. It must be emphasized that pregnancy itself is one of the main reasons why bred mares do not show signs of heat.
  • Minimize contamination of the reproductive tract by wrapping the mare's tail and scrubbing the vulva and surrounding area with an antiseptic such as povidone iodine soap (Betadine scrub). After scrubbing, the vulva should be thoroughly rinsed with warm water and dried. Additionally, the veterinarian should always wear a clean sleeve and surgical glove when introducing the arm into the vagina of the mare.

    Maiden mares may bleed slightly when the vagina is bridged due to rupture of the hymen. This has no clinical importance and will resolve spontaneously.

    The combination of culture and biopsy will provide a very accurate representation of the reproductive health status of the uterus:

  • To minimize contamination of the uterus or sample, the culture is taken with a double guarded culture swab. This is a swab protected by two plastic sleeves, and therefore the swab itself is pushed forward and just exposed to the uterine lining once the whole device has been inserted through the cervix. The sample is appropriately packaged and usually sent to a laboratory for culture.

    Results of bacterial culture must be interpreted with caution and in accordance with clinical signs and biopsy results. A positive culture is not always indicative of endometritis (uterine infection) or the need for antibiotic treatment. Additionally, there is controversy as to using uterine swabs as screening techniques for premating diagnosis of endometritis, as requested in some stallion service contracts. In general, if the mare has no history suggesting a problem and an intact hymen, culturing maiden mares is unnecessary and if done careless may actually induce and infection in an otherwise normal mare.

  • The tissue sample for endometrial biopsy is taken with specially designed alligator forceps, placed in a tube with formalin (fixative) and also sent to the laboratory for processing and interpretation. If performed properly, this is not a painful or dangerous procedure for the mare and will not affect her future fertility. The tissue sample obtained is observed under a microscope and yields important information in regards to the presence of active inflammation (consistent with infection) or the presence of degenerative changes that will reduce the mare's capability to sustain an early pregnancy and carry a foal to term.

    As part of the exam, a speculum (sterile piece of plastic or carton tubing) is also introduced in the vagina. With the aid of a penlight, this allows visualization of abnormalities in the vagina such as inflammation (vaginitis), scar tissue, or pooling of pus or urine. To diagnose problems of the cervix the veterinarian must carefully feel the cervical canal with the fingers while the hand is inserted in the vagina of the mare. This is the only accurate way to diagnose problems such as old tears or scars resulting from previous difficult foaling. This procedure is more valuable if performed when the mare is not in heat.

    A mare does not pass or fail a BSE, but all results are pooled together to ascertain the likelihood of a mare to become pregnant and/or carry a foal to term, and to determine whether the mare requires any specific treatment prior to breeding. Some common problems that can be diagnosed during a routine BSE include:

  • Pneumovagina (windsuckers). This means aspiration of air into the vagina, which usually continues into the uterus, predisposing the mare to vaginal and uterine inflammation and infections. It is usually due to incompetence of the vestibulo-vaginal sphincter and/or poor vulvar conformation. This is surgically treated, most commonly by suturing about two thirds of the length of the vulvar lips together (Caslick's operation or episioplasty). Do not forget that all mares with a Caslick's in place must be opened for breeding and especially prior to foaling.
  • Urovagina or urine pooling. This means accumulation of urine in the vagina of the mare, usually associated with poor conformation and/or pneumovagina. It can also be the result of previous foaling injuries affecting the reproductive canal or urethral opening. This can be treated surgically by repairing the opening of the urethra. It is commonly combined with a Caslick's operation.
  • Endometritis. This means uterine infection and can only be diagnosed with certainty by comparing the results of complete reproductive exam, culture and biopsy of the endometrium. In true uterine infections, the culture result indicates the presence of a true pathogenic (disease causing) organism (bacteria or fungus), and the interpretation of the biopsy shows the presence of inflammatory cells (white blood cells). Endometritis is treated with uterine lavages and antibiotics based on culture and sensitivity results.
  • Uterine cysts. These are dilated lymphatics relatively common in the uterus of older mares and they seldom affect fertility. When their effect on fertility is a concern and no other problems have been diagnosed, cysts may be removed manually or with the aid of a biopsy instrument. There are many fancy/expensive laser techniques described for removal of these cysts, but the effectiveness of these treatments and, especially, long term effects on fertility, have not been investigated.
  • Periglandular fibrosis / cystic glandular distension. These are degenerative changes of the uterine lining, most common in older mares or mares whose uteruses have been wrongly treated with caustic solutions such as povidone iodine or clorhexidine. These are irreversible changes and there is no appropriate treatment. Diagnosis is performed by interpretation of the uterine biopsy tissue sample.

    The main problem associated with these changes is early embryonic loss, since the equine embryo depends on the secretions from the uterine glands until the placenta forms at 50 to 60 days of pregnancy. Please note that although these are chronic (long term), degenerative changes of the endometrium, the term endometriosis (exclusively a human problem) does NOT apply to horses. This term is mistakenly used in equine reproduction and often seen in horsemen and even veterinary oriented magazines, journals and textbooks.

  • Cervical tears. These tears are usually due to previous difficult foaling (dystocia). The cervix no longer acts as a barrier for the uterus. Most tears can be treated surgically, but require expertise and special instruments.

    In summary, always request a complete reproductive history and BSE when purchasing a broodmare. If a mare has a history of infertility and no obvious problems are detected on a routine exam performed by your veterinarian always seek a second opinion. Chances are that your equine veterinarian and a reproduction expert (certified by the American College of Theriogenologists) can work together at diagnosing and managing your mare's reproductive problems.

  • number-of-posts0 paws up