Endometritis Classifications and Treatment

Many mares which cycle, but fail to conceive, have infections in their reproductive tracts. Hence, they are sometimes called "dirty" mares. The more scientific term for their problem is endometritis, which refers to the acute or chronic inflammatory process involving the endometrium (the inner lining of the uterus). Reduced fertility associated with endometritis—both acute and chronic—has been recognized for many years in broodmares. This subfertility is due to an unsuitable environment within the uterus for the developing conceptus, and in some cases the endometritis causes early regression of the corpus luteum (CL). These changes frequently occur as a result of microbial infection, but they also can be due to non-infectious causes. One of the main obstacles in producing the maximum number of live, healthy foals from mares bred during the previous season is the mare which is susceptible to persistent, acute endometritis following breeding.

The following is a classification system for equine endometritis:

  • Venereal infection;
  • Chronic infectious endometritis;
  • Endometrosis (chronic degenerative endometritis);
  • Persistent mating-induced endometritis (delay in uterine clearance).

The uterine lumen of the normal fertile mare is sterile despite the fact that the reproductive tract is contaminated with bacteria from the act of breeding, foaling, and veterinary procedures. Mares with defective vulval conformation can suck air and bacteria into the vagina, which can develop into endometritis.

The uterus responds to these bacteria with a rapid influx of neutrophils. Normally these neutrophils kill the bacteria rapidly (within 24 hours). These inflammatory by-products then are mechanically removed and the endometritis resolves itself (returns to normal). Failure to resolve this inflammation results in the "susceptible" mare. Susceptible mares have a delay in uterine clearance and the inflammatory by-products accumulate as uterine fluid. Such mares have a reduced pregnancy rate due to an unsuitable environment for the early developing conceptus.

Diagnosis Of Endometritis

Endometrial Culture And Cytology—A diagnosis of endometritis can be made by collection of concurrent endometrial swab and smear samples during early estrus for bacteriological culture and cytological examination, respectively. This allows time for resolution prior to breeding, and maximizes the chances of pregnancy. The ideal technique should ensure that the swab enters the uterus and collects bacteria from only the uterine lumen. It is important to ensure that the method of swabbing does not introduce bacteria into a previously normal uterus.

An air-dried smear is made by gently rolling the second swab either on a pre-stained slide or a clean, dry, microscope slide. The stained smear should be examined for inflammatory and endometrial cells , the latter confirming contact of the swab with the endometrium.

Interpretation—A positive culture result, with no evidence of inflammatory cells in the smear (usually neutrophils), is likely due to contamination during collection. Diagnosis of acute endometritis is based on the presence or absence of significant numbers of neutrophils in the smear. Mares which have greater than five neutrophils/high power field (x40) on a cytology smear should be considered as having active endometritis.

Endometrial Histology—In some cases, removing a small piece of uterine tissue for examination under a microscope—known as an endometrial biopsy—can be useful. The technique involves the insertion of a biopsy instrument through the cervix and into the uterus. With the biopsy instrument in the uterine lumen, a gloved hand is inserted into the rectum to allow manipulation of the instrument into the desired position. The sample is taken by closing the jaws of the instrument and tugging sharply. The endometrial biopsy sample should be sent to a laboratory that is experienced in evaluating samples.

Detection Of Intraluminal Uterine Fluid Using Ultrasound Imaging—Ultrasonography provides a rapid, non-invasive method of assessment of the uterus. In a study involving the ultrasonic examination, cytological, and bacteriological sampling of the uterus in 380 broodmares before breeding, the author concluded the following:

  1. If no free fluid is detected during estrus, then acute endometritis as detected in cytology is absent in 99% of cases.
  2. Free fluid does not indicate inflammation.
  3. Endometrial cytology and culture fail to detect sterile fluid accumulations.

Therefore, in mares which are particularly susceptible to endome-tritis and where vaginal interference should be minimized, endometritis often can be diagnosed on the basis of fluid in the uterus. If fluid is seen in the uterus, or where there are signs of vulval discharge or a short luteal phase, swabs should be taken to determine the cause.

Uterine Luminal Fluid—Since the identification of small volumes of intrauterine fluid via ultrasound by Professor O. J. Ginther’s laboratory in the mid-1980s, general awareness of the frequency of this abnormality has increased. Endometrial secretions and the formation of the small volume of free fluid might be associated with the same mechanism that causes normal edema during estrus. In many cases, the uterine luminal fluid that accumulates before mating is sterile and contains no neutrophils. The importance of these sterile fluid accumulations to endometritis is that, although initially sterile, the fluid might act as a culture medium for bacteria to multiply that gain entry to the uterus at mating and could be spermicidal.

The amount of fluid that should be considered significant is not clear, and it could be that quantity is more important than nature. This is particularly true of fluid appearing during estrus. The significance depends to some extent on when during estrus the fluid is observed: fluid detected early in estrus might disappear when the mare is further advanced in estrus and the cervix relaxes more. In the author’s experience, small volumes of intrauterine fluid during estrus do not affect pregnancy rates in contrast to mares with larger (greater than 2 cm depth) collections of fluid.

If there is more than one centimeter of fluid during estrus, your veterinarian probably will attempt to remove the fluid (using oxytocin) prior to breeding. If the volume is more than two centimeters, the fluid might need to be drained and investigated for the presence of inflammatory cells and bacteria. The mare might need a large volume uterine lavage. Intrauterine fluid during diestrus is indicative of inflammation and associated with subfertility due to early embryonic death and a shortened luteal phase.

Your veterinarian can grade intraluminal uterine fluid from I to IV according to the degree of echogenicity. The more echoic the fluid, the more likely the fluid is contaminated with debris, including white blood cells. However, cellular fluid can appear relatively anechoic, so care is needed in interpretation. Inspissated (thickened) pus can be so echoic that it is overlooked.

It could be that the actual appearance of the fluid and the ultrasonographic appearance are not as closely linked as once thought. Ultrasonographic appearance might be proportional to the size and concentration of particulate matter within the fluid, rather than the viscosity of the fluid. For example, purulent exudates can appear non-echogenic. Air has hyperechoic foci, and fluid with air bubbles appears cellular. Urine in the bladder can appear echoic, despite being a watery liquid. Your veterinarian can show these differences to you.

Treatment Of Venereal Infections And Chronic Infectious Endometritis

Any mare which is suspected of having a venereal infection must not be bred. In the case of clitoral infections, appropriate topical treatment is used. Clitorectomy might be necessary in refractory cases.

Chronic infectious endometritis is found most frequently in older mares which have had several foals. Such mares have a breakdown in uterine defense mechanisms that allows the normal genital flora to contaminate the uterus and develop into persistent endometritis. The approach to treatment most favored by practitioners has been the infusion of various antibiotics—dissolved or suspended in water or saline—into the uterine lumen during estrus. The intrauterine route is preferable to systemic therapy as most acute endometritis cases are localized. Systemic treatment alone or in combination with local application is suitable in a few circumstances.

Ideally, the choice of antibiotic for local treatment should be based on antibiotic sensitivity tests. In many cases, this is not possible and a broad-spectrum combination should be used that is effective against the mixed aerobic and anaerobic infections that commonly occur.

The author’s use of a specially formulated broad-spectrum, non-irritant, soluble preparation has not resulted in superinfection with Pseudomonas spp., Klebsiella spp., yeasts, or fungi. The number of treatments required depends on individual circumstances, but daily infusions by a veterinarian for three to five days during estrus work well in most cases.

The success of this treatment can be monitored using ultrasonography to identify the presence of intrauterine fluid.

When antibiotics are combined with oxytocin, a single daily treatment for three days has, in many cases, proved successful. Repeated endometrial swab/smear examinations can be used to monitor the response to therapy; however, every time the cervix is breached, there is the risk of introducing more bacteria. An indwelling intrauterine device has been used to retain a narrow-diameter infusion catheter within the cervix; however, there is a risk of ascending infection.

In addition to the antibiotic therapy, repeated treatment with prostaglandin F 2-alpha (PGF2-alpha) or its analogs increases the frequency of the follicular phases, thus allowing intrauterine therapy to be used more readily. In addition, it also reduces the duration of the luteal phase in which progesterone increases the susceptibility to infection. Estrus, itself, with its heightened defensive mechanisms, has a beneficial effect on preventing infections. Therefore, shortening the intervals between heats can be an adjunct to treatment in its own right. Predisposing causes to the persistent endometritis, such as defective vulval conformation, also should be addressed.

Fungal Infections

Mycotic endometritis is not as common as that of bacteriological origin, but recognition of a fungus as the causal agent is important since commonly used intrauterine antibiotic therapy is ineffective. In cases of fungal endometritis, mares might have a history of normal or abnormal estrus cycles, they might be anestrous or barren, or they might have had a recent abortion or a fetal membrane retention. There also could be a history of repeated intrauterine antibiotic therapy. The diagnosis is based on the presence of fungal elements and inflammatory cells in endometrial smears.

Successful culture of endometrial smears for fungi can be difficult because the organisms might be present in low numbers and they require a long incubation period. These infections are very difficult to treat, particularly if they are chronic or deep-seated infections and tend to recur.

The prognosis for the subsequent fertility of mares with mycotic endometritis is poor. If there is no success in eliminating the yeast or fungal infection after three attempts, the owner must be advised of the unlikely chance of success. It is suggested that a normal, healthy uterus can eliminate mycotic infection; this means that even if the mycotic infection is successfully treated, the mare must be viewed as a susceptible mare.


At the first international symposium on equine endometritis held in Newmarket in 1993, Professor Bob Kenney suggested that the term endometritis should not be applied to the degenerative changes within the endometrium often associated with age and parity. The old term "chronic degenerative endometritis" should be replaced by "endometrosis." Endometrosis can, therefore, be defined as the collective term to describe the wide range of degenerative changes (fibrosis and glandular degenerative changes), and the condition is diagnosed by endometrial biopsy.

Successful treatment of endometrosis is difficult. Improved fertility after endometrial curettage has been reported. This has involved the use of mechanical and chemical agents (namely povidone-iodine and kerosene) that cause endometrial necrosis. This treatment, apart from being of questionable efficacy, can cause irreversible damage, such as adhesions. Repeated daily lavage with two to three liters of hot (50 C), sterile, isotonic saline has been suggested as a method of reducing the size of the lymphatics and thereby the whole uterus. The prognosis for fertility remains poor whatever treatment is used.

Persistent Mating-Induced Endometritis

Uterine Defense Mechanisms—At breeding, the mare’s uterine lumen becomes contaminated with microorganisms and debris. Even if mares are bred by artificial insemination, semen is deposited directly into the uterus. In addition, it recently has been shown by workers in Finland that spermatozoa without bacterial contamination induce an uterine inflammatory response. The intensity of the reaction was dependent on the concentration and/or volume of the inseminate (e.g., frozen semen induced a stronger inflammatory reaction in the uterus then fresh or extended semen). The intensity of the inflammatory response following insemination depends on the sperm themselves rather than any extender and is not different for live or dead spermatozoa.

In most mares, this transient endometritis resolves spontaneously within 24-72 hours so that the environment of the uterine lumen is compatible with embryonic and fetal life. It is important not to regard this endometritis as a pathological condition. Rather, it is a physiological reaction to clear excess sperm, seminal plasma, and inflammatory debris from the uterus before the embryo descends from the oviduct into the uterine lumen 5 1/2 days after fertilization. However, if the endometritis persists after Day 4 or 5 of diestrus, in addition to being incompatible with embryonic survival, the premature release of PGF2-alpha results in luteolysis and a rapid decline of progesterone and an early return to estrus. These mares are referred to as susceptible, and they develop a persistent endometritis.

In general, reduced resistance to endometritis is associated with advancing age and multiple foalings. Susceptibility to endometritis is not an absolute state since failure of uterine defense mechanisms needs only slow the process of eliminating infection. In the practice situation, a wide range of susceptibility to endometritis is seen and, in the author’s view, it must not be thought that mares can be neatly packaged into "resistant" or "susceptible."

Studies on immunoglobulins, opsonins (substances that bind to particulate antigens and induce phagocytosis), and the functional ability of neutrophils in the uterus of susceptible mares have not confirmed the presence of an impaired immune response. Work from New Zealand in the mid-1980s first suggested that reduced physical drainage might contribute to an increased susceptibility to uterine infection. The physical ability of the uterus to eliminate bacteria, inflammatory debris, and fluid now is known to be the critical factor in uterine defense. It is a logical conclusion that any impairment of this function (i.e. defective myometrial contractility) renders a mare susceptible to persistent endometritis.

The reason susceptible mares have this defective contractility is not known. Recently it has been suggested by workers from the veterinary school at the University of California, Davis, that the regulation of muscle contraction by the nervous system might be impaired. The resulting fluid accumulation could be due to failure to drain via the cervix or decreased reabsorption by lymphatic vessels. Lymphatic drainage could play an important role in the persistence of post-breeding inflammation, and it is interesting that lymphatic lacunae (lymph stasis) is a common finding in endometrial biopsies taken from susceptible mares.

Detection Of The Susceptible Mare

This can be difficult as there might only be subtle changes in the uterine environment that are not readily detected by current diagnostic procedures. Many mares show no signs of inflammation before breeding, but fail to resolve the inevitable endometritis that follows breeding.

History is perhaps the most useful indicator of a susceptible mare in practice. Demonstration of clearance failure using response to bacterial challenge and scintigraphic methods have been used to identify that a mare has a clearance problem, but they are difficult to apply in practice. Use of the ultrasound to detect uterine luminal fluid appears to be the most useful technique in practice.

In the author’s opinion, the presence of free intraluminal fluid prior to breeding strongly suggests susceptibility to persistent endometritis. It currently is not known for certain whether the fluid accumulates due to an excess production, a delay in physical clearance via the open cervix, or decreased reabsorption by lymphatic vessels. It might involve all three.

The Old Maiden Mare Syndrome

It is particularly important to recognize and manage appropriately the older maiden mare, as in many cases these mares are susceptible to post-breeding endometritis even though they have never been bred before. Often sport or Warmblood mares might not be presented to be bred until they are in their teens, and these older maiden mares can be very difficult to get in foal.

Many of these mares have some common characteristics, which resemble a syndrome. Dr. Sidney Ricketts and his team in Newmarket have found that endometrial biopsy samples reveal glandular degenerative changes and stromal fibrosis (endometrosis) as an inevitable consequence of aging despite the fact the mares have not been bred. Another of the most common characteristics of these mares is uterine fluid. Often an older maiden mare has an abnormally tight cervix that fails to relax properly during estrus so that fluid is unable to drain, and thus it accumulates in the uterine lumen. In many cases, this fluid is negative for bacterial growth and presence of neutrophils.

Once the mare is bred, the fluid accumulation will be aggravated due to poor lymphatic drainage and impaired myometrial contraction, compounded by the tight cervix. The amount of intrauterine fluid will vary in individual mares, ranging from a few milliliters to more than a liter in extreme cases. To maximize the fertility of these mares, it is vital that the veterinarian be aware of the possibility of this type of uterine and cervical pathology. All too often owners assume that the fertility of these mares is comparable to that of young maiden mares; one of the most important aspects of breeding the old maiden mare is to make the owner aware that there is a high possibility that she will be a problem. These mares must be considered highly susceptible and managed accordingly.

Treatment Options For The Susceptible Mare

The aim of the treatment should be to assist the uterus to clear physically the normal inflammatory byproducts of the response to breeding. Since within four hours of mating the spermatozoa necessary for fertilization are present within the oviduct, and since the embryo does not descend into the uterus for about 51Ú2 days, mares can be treated safely from four hours after mating until three days from ovulation, providing non-irritant therapy is used.

However, progesterone concentrations rise rapidly following ovulation in the mare, and it is preferable to avoid treatment involving uterine interference beyond two days after ovulation. This is because the mare has her highest resistance to infection around ovulation, and the further you get away from the time of ovulation, the lower her resistance.

Both coitus and artificial insemination can be a source of uterine contamination. Remember, spermatozoa themselves are responsible for initiating a marked inflammatory response. The successful management of susceptible mares logically should require some form of post-mating therapy, such as intrauterine antibiotic infusion, uterine lavage, and intravenous oxytocin. These can be used alone or in combination. The emphasis should be on treatment in relation to breeding and not ovulation. Too often in the past, veterinarians have waited until ovulation before treating these mares. By then, there usually has been a large accumulation of fluid and the bacteria are in a logarithmic phase of growth.

Uterine Lavage—Recognition of the importance of the mechanical evacuation of uterine contents accounted for the introduction of large-volume uterine lavage. The technique involves the mechanical suction or siphonage of two to three liters of previously warmed (to 42¡ C) sterile physiological (buffered) saline or lactated Ringer’s solution infused into the uterus via a catheter that has been retained within the cervix via a cuff. The most convenient is a large-bore (30 French, 80 cm) autoclavable equine embryo flushing catheter. The cuff is useful as it effectively seals the internal cervical os. The catheter only should be inserted after thorough cleansing of the perineum. The rationale for such an approach are these:

  1. The removal of accumulated uterine fluid and inflammatory debris that can interfere with neutrophil function and the efficacy of antibiotics;
  2. Stimulation of uterine contractility;
  3. Recruitment of fresh neutrophils through me-chanical irritation of the endometrium.

The saline is infused by gravity flow one liter at a time, and the washings inspected to provide immediate information concerning the nature of the uterine contents. The lavage should be repeated until the fluid that is recovered is clear. In most cases, the fluid evenly distributes in both horns, making transrectal massage of the uterus unnecessary. If a rectal examination is performed while the catheter is in the uterus, your veterinarian will be very careful to avoid contaminating the catheter. The fluid should be recovered in the same container in which it is infused, thereby preventing air being aspirated into the uterus via the catheter.

Measurement of the recovered fluid and ultrasonographic examination of the uterus should be performed after flushing to ensure that all the fluid has been recovered. This is necessary because you are dealing with a mare with an impaired ability to drain the uterus spontaneously. For that reason, the process usually is combined with oxytocin treatment.

Ideally, these mares will be bred only once, but if repeated matings are necessary, uterine lavage should be performed after each mating. Large volume lavage is beneficial in many cases, particularly the mare with a relatively large (above two centimeters in depth) accumulation of fluid after breeding. The process is time-consuming, and there is the possibility of further contamination of the uterus by passage of a drainage tube. Nonetheless, where there are more than two centimeters of uterine fluid, or where a mare is known to be highly susceptible, the risks are outweighed by the benefit of treatment.

In controlled studies in which a single bacterial species was infused into the uterus and lavage was within 12 hours of mating, saline lavage and uterotonic drugs such as prostaglandin F2-alpha are as effective as antibiotics in eliminating bacteria from the uterus. However, under normal clinical conditions, there is a mixed bacterial contamination, and lavage cannot always be performed within 12 hours. This is the reason the author prefers continued use of intra-uterine antibiotics as part of the therapeutic protocol.

Oxytocin—A hormone produced by the pituitary gland, oxytocin once was believed to exert an effect on uterine contractions only during the period immediately before and after foaling. Demonstration of its action in mares which are cycling has had a major impact in the management of post-mating endometritis. Thus, oxytocin provides an ideal approach to evacuating uterine fluid by stimulating contractions of uterine muscle. The advantage of a pharmacological method of emptying the uterus over mechanical means such as lavage has been striking. Oxytocin is particularly effective during estrus, when the cervix is relaxed, thus is well-suited to post-breeding therapy. Shortly after ovulation, when the cervix begins to close, oxytocin becomes less effective in stimulating contractions.

Small doses of oxytocin, in the range of 20-25 international units, are administered intravenously or intramuscularly, resulting in fluid evacuation by 20-30 minutes. No colic signs are noted at this dose, although mild sweating is not uncommon. Doses as low as 10 units have been used with similar results. The drug is believed to work directly on the uterine muscle and indirectly by causing a release of prostaglandins, compounds that also stimulate uterine contractions. It is interesting to note that anti-inflammatory drugs such as phenylbutazone depress the production of prostaglandins and might interfere with uterine emptying. Thus, mares on long-term phenylbutazone therapy could be candidates for oxytocin therapy post-breeding.

Prostaglandin Analogs—Since endo-metritis stimulates the production of prostaglandins from the uterine lining, it obviously functions in the natural defenses of the uterus. With this in mind, prostaglandins have been used in treatment of mares with defective uterine clearance. The most useful of these compounds is cloprostenol, which has a longer duration of action than the natural prostaglandins. However, oxytocin remains the author’s drug of choice for mares which retain uterine fluid.

Intrauterine Plasma Infusions—Based on the research findings in the 1970s and 1980s that emphasized the immunological aspects of the uterine defense mechanisms, intrauterine plasma as a source of immunoglobulins has been used in the susceptible mare. Since mares which are susceptible to endometritis do not possess a quantitative deficiency of immunoglobulins, it is questionable if such treatment is truly effective. Consequently, plasma is best used in mares which repeatedly fail to become pregnant, but have no history of fluid accumulation.

Management Protocols

A mare which from past experience/history is known to produce a large amount (several centimeters depth) of luminal fluid after mating should, in the author’s experience, be managed using the following protocol.

  • Overall management of such mares must be excellent prior to breeding.
  • Gynecological examinations, particularly of the vagina, should be performed as aseptically as possible.
  • Thorough digital examination of the cervix can identify fibrosis, lacerations, or adhesions that might need treatment before breeding.
  • Since air in the vagina can cause irritation of the mucosa, it should be expelled by applying downward pressure with the hand through the rectal wall.
  • Attention to hygiene at mating should include using a tail bandage and washing the mare’s vulva and perineal area with clean water (ideally from a spray nozzle, which avoids the need for buckets).
  • Breeding should occur at the optimal time, and the number of breedings should be minimized. This means that these mares need very close monitoring of the estrous period by rectal palpation and ultrasonography.
  • The use of drugs such as human chorionic gonadotrophin (HCG) to induce ovulation is strongly recommended in such mares in an attempt to ensure they are only bred once.
  • Prediction of ovulation can be made easier by not breeding these mares too early in the year, i.e., before they have begun to cycle regularly.
  • If feasible, the use of artificial insemination can be helpful to reduce (but not eliminate) the inevitable post-breeding endometritis.
  • A single breeding must be arranged one to two (or even three) days before the anticipated time of ovulation. It is my experience that most stallion spermatozoa are viable at least 48-72 hours after mating. In any case, records based on previous early pregnancy examinations will indicate if the semen from a particular stallion is not viable after 48 hours. This early mating allows more time for drainage of fluid via an open cervix and also utilizes the natural resistance of the reproductive tract to inflammation during estrus.
  • In the author’s opinion, treatment for endometritis ideally is performed on the day before, or the day of, ovulation. Progesterone concentrations rise rapidly in the mare, and any post-ovulation treatment has an increased risk of uterine contamination. In addition, uterine fluid is less likely to drain if the cervix is beginning to close.
  • Ultrasound examination of the uterus three to 12 hours after mating should be performed to assess the amount and echogenicity of any intrauterine fluid. This examination and treatment of mares very soon after mating (before the bacteria long have been in a logarithmic growth phase) is important for the susceptible mare. Treatment has been successful as early as two hours after mating.
  • Lavage the uterus with one to two liters of warmed, buffered, sterile saline followed by intravenous administration of oxytocin. In cases where the cervix has failed to relax adequately, digital manipulation is performed. This is one reason for ideally treating the susceptible mare before ovulation; a second reason is that oxytocin is less effective at increasing uterine pressure once the mare has ovulated.
  • After 20 minutes, the mare should be re-examined and any fluid pooling in the vagina removed. This is followed by infusion of a low volume (30 ml) of water-soluble, broad-spectrum antibiotics such as already described (Utrin Wash, Vetoquinol UK LTD, Bicester) into the uterus via a sterile irrigation catheter.

I use a low volume of antibiotic solution as, if these mares have a drainage problem, it seems logical to use the minimum effective volume. Older, pluriparous mares might need larger volumes (up to 100 ml). It is my experience that with larger volumes (above 150 ml), some of the solution is lost via cervical reflux. It is vital that the antibiotic used does not irritate the endometrium or predispose to overgrowth with fungal organisms. Neither of these problems has been observed using the antibiotic combination described here. I leave 2 x 25 iu of oxytocin to be given by the stud farm personnel that evening and again in the morning. This is by the intramuscular route. In mares with lymphatic stasis, the slower release of prostaglandin (cloprostenol 500mcg IM) can be useful in addition to oxytocin. The cloprostenol should be given six to eight hours after the first oxytocin injection. The mare is re-examined the following day and oxytocin treatment repeated if fluid still is present. Only rarely will a second infusion of antibiotics or a lavage procedure be performed due to the risk of uterine contamination. Evaluation of the uterus post-breeding is a crucial time to assess all mares. Susceptibility to endometritis is not an absolute state: failure of the defense mechanisms only needs to be of the degree necessary to slow the process of clearance past a critical point. As many stud farms are visited on an every-other-day basis for routine reproductive work, treatment schedules should be based around a visit. Most multiparous mares are at risk for either clinical or subclinical endometritis following insemination, be it natural or artificial. The treatment adopted should be based on history and clinical findings, including ultrasonographic evaluation of the uterus after breeding. An important concept is to treat in relation to breeding and not wait for ovulation.

Remaining Questions

There are valid concerns that the early embryonic/fetal loss rate of susceptible mares with endometritis which receive aggressive post-mating therapy will be much higher despite the temporary improvement in uterine environment. Undoubtedly, the live foal rate of mares which are extensively treated post-breeding is less than in young, genitally healthy mares. However, susceptible mares often are old and frequently when uterine biopsy results are available, they often confirm degenerative changes within the endometrium. Consequently, one’s live foal rate expectations are lower in these mares.

This is not a reason not to treat mares post-mating, in my opinion. Of course, one should optimize the chances for conception by the methods discussed above, but even when all these techniques of management, pre-breeding examination, etc., are applied, the susceptible mare still should be treated after breeding.

At what point the susceptible mare should be bred and when she should be treated and either short cycled or bred at the next natural estrus are difficult to be dogmatic about. This must be a matter of clinical experience based on history and findings of clinical and laboratory examinations.

About the Author

Jonathan F. Pycock, B. Vet. Med, PhD, DESM, MRCVS

Jonathan F. Pycock, BVetMed, PhD, Dipl. ESM, MRCVS, operates Equine Reproductive Services, a first opinion and referral private equine practice based in Yorkshire, England. He has published many papers and book chapters on a variety of equine reproductive topics, and edited the book Equine Reproduction and Stud Medicine. His main interests include ultrasonography, breeding the problem mare, and artificial insemination. Currently, he is evaluating the use of oxytocin and depot oxytocin as a post-breeding treatment for mares.

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