An STL model of the equine uterus

Keywords: model, 3D, STL, equine, uterus.

The author has used a stereolithographic (STL) file to view and print equine uteruses and pelvic structures in 3D.

NEW: This, small file can even be downloaded on a cell phone. Pay no attention to dialog alluding to processing of the file. Go ahead and download it. With the App "Fast STL viewer" (see Google play store) already downloaded on your phone, click on this downloaded file (not the App itself!) and the uterus will appear on your phone as shown in the thumbnail above. Incidentally, the same file can be downloaded and viewed on your laptop. 

Viewing the model:

For STL viewing alone on your laptop the author suggests that you download this file. Click on it and your laptop (PC or Apple) will bring up a suitable program for viewing. An example of  such an interface is shown below. 

Printing the model:

Custom STL printing can be done through Axis Prototypes in Montreal after contacting the author.  Axis holds the right to a digitally engineered model of the tract and pelvis that is ready for printing. High quality prints such as those seen here are not inexpensive.  Printing a 25 cm model (caudal to cranial) printed from STS nylon will cost approximately $600 Can. ($460 US). 

Manipulating the model:

In the absence of a real uterus or a printed tract, this digital model serves to remind one of many practical aspects of equine reproduction  A short list comes to mind immediately. Some may wish to print this list so that it can be referred to as the model is manipulated. Better still, manipulate the model on a cell phone while reading the learning points on a laptop.

1.Rotate the tract for a view of the vulva lips and clitoris. Be reminded of its "winking" appearance often, but not exclusively, seen during estrus. Note the importance of the clitoris in diagnosis of CEM and the conformation of the vulva lips in infertility. 

2.Enter the vagina and move cranially until the external urethral orifice is encountered. Note that the hymen is normally found just cranial to the orifice but is absent here because this tract was modeled from that of a pluriparous mare. At this point, one should also contemplate the potential problem of urine pooling in the cranial vagina in older mares due to splanchnoptosis.

3.Traveling further cranial in the vagina, one can see the opening of the cervix, showing its dorsal frenulum. Consider the simple nature of the equine cervix compared to that in other species i.e. there are no transverse cervical rings and the cervix is easily dilated for artificial insemination, embryo collection and is even distensible enough to remove fetuses that are three or four months old. The same distensibility is certainly not encountered in ruminants and other domestic animals.

4.Turning to the left and right at a point just caudal to the cervix, one should be reminded that the vagina lies completely within the peritoneal cavity at this point. This is important because it permits one to penetrate the cranial vagina for standing ovariectomy in mares. It also means that if the cranial vagina is torn during foaling, evisceration can occur from this site.

5.Withdraw from the vagina and rotate the model so that the cervix is visible from within the peritoneal cavity. Note that the cranial portion of cervix is firmly suspended between the ilial shafts on either side, by the mesocervix i.e. the caudal portion of the mesometrium. This is significant because the cervix of a mare cannot be grasped, elevated and manipulated as it can in a cow.

6.Rotate and tilt the model so that the mesometrium, containing the uterine artery (middle uterine artery) can be seen clearly. Be reminded that a uterine artery can be forced back against the shaft of the ileum during foaling, rupturing the vessel, causing severe hemorrhage within the mesometrium. Unlike the situation in cows, there is no fremitus in this artery during pregnancy.

7.Rotate the model so that the attachment of the mesometrium the uterus along its lateral borders can be appreciated. Note in turn, how the mesometrium is attached to the abdominal wall on either side. This firm attachment affords substantial stability to the equine uterus and explains in part why uterine torsion is less common in mares than it is in cows. It also means that the equine uterus cannot be retracted during palpation as is done in cattle.

8.Rotate the uterus so that the intercornual ligament is visible. Although it is fairly well-developed. It is never used to retract the uterus  for reasons just mentioned.

9.Tilt the uterus so that its dorsal surface is visible, showing how the bifurcation of the uterine horns provides a T-shaped structure instead of the Y-shape characteristic of the bovine uterus.

10.Rotate the uterus up and down on it's transverse axis, noting the length of the uterine body in a mare compared to the very short body in ruminants. This has many implications. For example, in cattle is very important to enter a particular uterine horn for insemination or embryo collection. In mares by contrast, the long uterine body means that semen is simply deposited anywhere in the body and during embryo collection, the embryo is collected from the uterine body.

11.Rotate the tract and pan in and out over the ovaries, noting their large size in comparison to those of cows. Be reminded that although equine corpora lutea are three or four times the diameter of bovine corpora lutea, they cannot be detected by transrectal ovarian palpation. This is because equine  ovaries are surrounded by thick tunica albugineae, disguising the presence of corpora lutea. Therefore, to determine if a mare is ovulating (in the absence of progesterone assay) one must use ultrasonography

12. Noticeably absent from this model are the ovarian bursae. The author apologizes for that oversight and time allowing, will add that in his next life.

Mullerian ducts in a male fetus. Uterus masculinus

Keywords: mullerian, male, female equine, uterus, masculinus

In males, the Wollfian (mesonephric) tubule system develops into the ducti deferentia, epididymides and  gubernaculae. In the presence of testicles, inhibin (produced by Sertoli cells) suppresses the development of what would otherwise be female genitals. Although the female (Mullerian or paramesonephric) system is suppressed, remnants are sometimes visible in the neonate or even adult animals. 

In this case (a 315 day old equine fetus) thread-like remnants of the mullerian system are clearly visible. Occasionally this structure is referred as the uterus masculinus. 

Image size: 3243x 2190px. Copyright: Dr Frederico Canisso. canisso@illinois.edu

Ultrasonography of intra- and extrauterine hemorrhage.

Keywords: ultrasound, hemorrhage, uterus, mesometrium, equine

1. A hematoma seen in the mesometrium (Me) at the time of foal heat breeding.  Like the majority of mares with mesometrial hematomas, this mare showed no outward symptoms at the time of foaling. The structure was clearly palpable per rectum; hence the ultrasonograph.

2. A similar hematoma to that described above but older, more consolidated and more echogenic.

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3. Intra uterine (IU) hemorrhage in a mature mare presented because of a foul smelling vaginal discharge at 35 days post foaling. The mare was systemically normal but ultrasonography and a glove hand examination of the uterus revealed masses of clotted blood, seen here on ultrasound in the left uterine horn. This was hemorrhage was presumed to be due to a severe partial thickness endometrial tear, sustained during parturition. The hooves of foals can cause these tears.

Most of the clotted blood was removed by hand then the uterus was flushed with saline. Antibiotics and tetanus toxoid were administered. The uterus appeared to be normal on ultrasonography at the time of discharge but the mare was lost to follow up.

4. Two images of an unusual intra-endometrial (IE) multilocular cyst at the approximate time of foal heat. Its contents were not consistent with the non-echogenic fluid usually seen in endometrial lymphatic cysts. However, this mare was known to have endometrial lymphatic cysts before she conceived. Therefore it is possible that this was a group of cysts that was traumatized during foaling, causing hemorrhage within the cysts.

Reference

Dolente, B.A. et al. 2005. Mares admitted to a referral hospital for postpartum emergencies: 163 cases (1992-2002). J.Vet.Emergency and Critical Care 15: 193-200

Uterine torsion

Keywords: uterus, equine, torsion, pregnant

Uterine torsion is a problem that generally occurs in the last half of gestation in mares.  This is very different to cows, where torsion is occurs during calving. Generally therefore, no consideration is given to delivering the foal after torsion is relieved; it would usually be too immature to survive.

Uterine torsion should be suspected in any mare that is pregnant, in advanced gestation and is presented with colic. Torsion is usually easy to diagnose because the mesometrial ligament is pulled tightly to one side and in most cases, is clearly palpable per rectum.

Image size: 1384 x 643px

This author and holder of copyright of this image is Dr G.F Richardson. (grichardson@upei.ca).

The basic principle for non-surgical correction of uterine torsion in mares is to introduce general anesthesia and to "roll the dam around her uterus" leaving her uterus behind (!)   The same philosophy is applied in cows except that general anesthesia is not required.

A plank such as that shown at left in the inset can be used to stabilize the uterus while the mare is rotated on her longitudinal axis.  In an effort to stabilize the uterus while the mares is rotated, pressure can be placed on the plank. As shown below, one may even wish to stand on the plank for additional pressure. Some have argued that the use of a plank is not essential to correct uterine torsion. This author suggests that its use is logical and potentially valuable.

Image size: 784 x 523px  Copyright of Dr J Dascanio. LMU College of Veterinary Medicine   john.dascanio@lmunet.edu

Transrectal examination after rolling will usually reveal if the torsion has been corrected. If an initial attempt fails, rolling should be repeated. When rolling fails altogether, the mare is recovered and a standing flank laparotomy is often used to correction of the torsion. However, a fairly recent paper by Jung et al, suggests that ventral laparotomy should be attempted in all cases, in preference to rolling.

Occasionally the foal dies as a result of blood vascular embarrassment and is aborted soon after the torsion is corrected.

Notes: 
The survival rate of foals is greater when torsion occurs earlier rather than later in gestation. This is probably because of tension on blood vessels, the possibility of uterine or mesometrial rupture and greater difficulty in correcting torsion due to its sheer weight in later gestation.

In rare cases, crossed and tense mesometrial ligaments cannot be palpated per rectum. It is not clear why this is the case but it does serve to remind one that torsion cannot be discounted if the history still points to uterine torsion. Apparently, torsion can be determined by palpation of the body of the uterus in those cases.

Reference:

Chaney, K.P. et al. 2006 Effect of Uterine Torsion on Mare and Foal Survival: A Retrospective Study 1985–2005 Proc. AAEP 52:402-403

Doyle, A. J. et al. 2002. Clinical signs and treatment of chronic uterine torsion in two mares J. Am Vet. Med. Assoc. 220:349-353

Jung, C et al. 2008. Surgical treatment of uterine torsion using a ventral midline laparotomy in 19 mares. Australian Vet.J. 86: 272-276

The reproductive tract of a 10 month equine fetus

Keywords: uterus, fetus, ovaries, equine, anatomy.

At about 90 days of gestation the fetal gonads of both sexes start to increase in size and reach maximum diameters at about 7 to 8 months of gestation. Interestingly, the growth is due to hyperplasia of interstitial tissue, not oocytes or seminiferous tubules. In fact, by 7 to 8 months the fetal ovaries are larger than the maternal ovaries. After this peak in gonadal growth, the fetal gonads decrease in size to about one tenth of fetal maximum.

Equine fetal ovaries in both sexes have long been known to be a substantial source of androgens. These androgens are aromatized to various estrogens. Increasing and decreasing estrogen production by the equine placenta during gestation (a feature often used in pregnancy diagnosis) parallels the growth and regression of the fetal gonads. However, it has only recently been shown that the gonads are also a substantial source of inhibin (not AMH) but the function of this inhibin production is not yet known.

In this ten month old equine fetus, the ovaries are still relatively massive.In the image below, the right kidney of the fetus lies between left and right ovaries. The uterine tube (fallopian tube) is shown here, crossing the ventral surface of the left ovary. The left and right horns and body of the uterus are also visible, a small fold in the caudal part of the uterine body, indicating the approximate location of the cervix.

Image size: 1500 x 1500px

The image below is a dorsal view of the excised tract seen above. The massive size of the ovaries compared to the rest of the reproductive tract is remarkable. The caudal part of the tract (from the cervix caudally) has been twisted anticlockwise to reveal the urethra (yellow arrow) and the clitoral sinus (green arrow). R= Rectum.  The small black arrow indicates the position of a partially perforate hymen!

The intercornual ligament (more of a feature of the bovine than the equine tract) is clearly visible here, as are the (middle) uterine arteries.

Image size: 1500 x 1130px

Selected reference:

Tanaka, Y et al. 20013. Localization and secretion of inhibins in the equine fetal ovaries. Biol.Reprod.328-335

Endoscopy and ultrasonography of pyometra

Keywords: pyometra, mare, uterus

This image shows the appearance of pyometra in the uterus of a mare during postmortem examination. In this case the condition was supported by a progestogenic environment; two corpora lutea (arrows) being visible on the right ovary. If she had not been euthanized, this mare would have been treated with prostaglandins and physical drainage.

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Pyometra may be characterized by a purulent discharge but often it is only discovered on routine ultrasonography.  The pus in cases of pyometra is often highly echogenic due to its cellular content. However, as seen in the inset ultrasonographic images shown here, it can be remarkably non-echogenic. In such cases, endoscopy will ascertain the diagnosis (seen inset image at upper right).

Pyometra and the use of intrauterine spheres .

Keywords: sphere, marble, uterus, pyometra, luteal

A 14-year-old Quarter Horse mare was presented for a chronic vaginal discharge of several months duration. Although there was a history of breeding, details of the breeding dates were unknown. Therefore a pregnancy diagnosis performed by the rDVM. This diagnosis was positive for pregnancy but was presumably not done with the assistance of ultrasonography (see below). A chronic discharge began after the pregnancy diagnosis and the rDVM and (presumably after a negative pregnancy diagnosis), the uterus was flushed with saline and intrauterine antibiotics were administered. The attending veterinarian reported  that there was a mummified fetus could be palpated within the uterus. Oxytocin was ineffective in expelling this object so the case was referred to the AVC.

Transrectal ultrasonography revealed a uterus flilled with moderately echogenic fluid. This is shown below. Although pus need not be echogenic, the appearance of this uterus was consistent with most cases of pyometra in mares. The image at left, shows a cross section of a uterine horn and the image at right, the body, adjacent to the cervix (arrow).

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The pyometra was supported by a corpus luteum in the left ovary:

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The highly echogenic object seen in this video was present close to the midline. Both observers (I wish to acknowledge the assistance of my colleague Dr B. Crane on this case) were initially startled at the extremely symmetrical and highly echogenic appearance of the calvarium of the supposed "mummified fetus". Our impression was that only the head of the mummified fetus remained! However it soon became obvious that this was some other sphere-like object; possibly a marble. The reader should recall that there was no history of any insertion of a marble in this animal.

Play the video here using the built in controller or click on the link in the image. The FULL SCREEN setting is not recommended because the video has been compressed for mobility.

Prior to extraction of the object, it was noted that a pre-existig tear was present in the cervix at the seven o'clock location. The depth of the tear was approximately 2 cm caudal to cranial. 

The mare was tranquilized with detomidine and analgesia was supplied with butorphanol. Over a 1 1/2 hour period, the cervix was gradually dilated using digital expansion. Then, using transrectal manipulation, the object was moved towards the cervix. A black glass sphere 3.5 cm in diameter (a "marble") was delivered through the cervix

Image size: 3325 x 4720 px

Following extraction of the marble, several liters of purulent material were drained from the uterus. The uterus was then flushed serially with a total of 15 L of normal saline. Ten million international units of sodium penicillin G. was instilled into the uterus and because of the presence of a corpus luteum in the right ovary, prostaglandin was administered to cause luteolysis.

The mare was discharged to the care of the referring veterinarian with instructions to re-evaluate her uterus in approximately 2 weeks and again several months later to exclude the possibility of chronic pyometra.

Notes: The use of marbles and other spherical structures has been investigated over the last 10 to 15 years in horses for the purpose of suppressing estrus in mares. The motivation behind doing so is to suppress estrus that is thought to compromise athletic performance or behavior while showing.  In some cases it has be used to prevent unwanted conception. As noted by Dr A. Tibary, a similar technique has been used by Bedouin camel herders, using date pits instead of marbles.

Interestingly, the correlation between estrous behavior and athletic ability has not been well studied and opinions are subjective at best.  This also applies to perceived links between the estrous cycle and problem behavior.  Serum progesterone samples taken during “problem” periods of behavior have led this author to believe that many such problems are not related to ovarian activity at all. That is not to say that they cannot be. Indeed the author has had first-hand and unequivocal experience of this on stud farms. However, when problems have been related to ovarian activity for lack of a better explanation, the diagnosis must be approached with circumspect. This is true even when the owner reports that performance or behavior has improved after treatment because owners seek to believe that the expense or discomfort for the mare was justified.  

Most important is that fact that it is often impossible to know if a mare is in estrus without force teasing (nose-to-nose; nose-to-tail) or ultrasonograpy even if her behavior on casual observation suggests otherwise. Indeed, it has been well established that ovariectomized mares and those with inactive ovaries can show overt signs of estrus. Also,  many cases of presumed estrus-associated behavior are reported in the winter when most mares are not cycling. 

  

When intrauterine spheres were used, some studies have shown that mares did not respond at all but in most studies, 40 to 75% of mares showed prolonged period of diestrus.  This is because the corpus luteum fails to undergo luteolysis. Failure of luteolysis is not a consequence of exhaustive release of prostaglandin but instead it appears to be because prostaglandin secretion is suppressed.   The reason for this is currently unknown (2013) and is especially perplexing because most of these spheres remain in the center of the uterus, close to the body, not migrating like conceptuses.

When a marble causes failure of luteolysis, the corpus luteum is retained for a variable period, but usually between 60 and 90 days; perhaps as long as 150 days in some cases. Obviously field-use of marbles is not usually accompanied by progesterone assays or routine teasing so an accurate estimate of the range of luteal retention is not available.

In this case, a 35 mm glass marble was present but silver, copper or glass or water filled plastic spheres have been used as well.  Smaller diameter marbles have also been used but published evidence (Nie, G.J. et al 2003) suggests that larger spheres are more effectively retained.

Most pertinent to this case is the fairly consistent finding in all studies that intrauterine “marbles” do not usually appear to cause endometritis or pyometra. In a few cases, only slight fluid accumulation and mild endometritis was present. Furthermore, in one study, treated mares had normal conception rates after the spheres were removed.  Therefore, it is probably not justified to imply that this marble was the cause of pyometra in this case. Indeed, the cervical tear in this case (and the age of the mare) probably played a greater role in the genesis of pyometra than did the intrauterine marble.

The use of marbles to suppress estrus in mares remains a contentious issue.

The ultrasound image of the marble lends itself to an interesting discussion on artifacts. Some of them are shown here. The pronounced acoustic interface is probably due to a gas bubble. Note the over-estimation of the size of the marble in the ultrasound image.

Image size: 637 x 450 px. With thanks to Dr Paul Rist (ACVR) pending changes

References:

1.  Hedberg, Y. 2006 Oestrus in the mare with emphasis on deviant behaviour and adrenal gland function Alm Acta Universitatis Agriculturae Sueciae ISSN 1652-6880  ISBN 91-576-7250-4
2. Turnbull,  E.B.  et al. 2010 The effect of intra-uterine devices on the reproductive physiology and behaviour of pony mares. The Vet J. 186: 39–46
3. Nie, G.J. 2001. Use of a Glass Ball to suppress behavioral estrus in mares  Proc. AAEP 47: 246 -248
4. Nie, G.J. 2003. Use of an intra-uterine glass ball protocol to extend luteal function in mares. J. Equine. Vet. Sci. 23: 266-273
5. Rivera del Alamoa, M.M. et al, 2008. Mechanisms behind intrauterine device-induced luteal persistence in mares.  Anim. Reprod. Sci.  107: 94–106

Endometrial biopsy cytology

Keywords: biopsy, equine, endometrium, uterus, infertility

Image size: 990 x 630px

This image shows margination of neutrophils (PMN) during estrus. This is a common phenomenon seen in endometrial biopsies especially but not exclusively during standing heat. Neutrophils attach to the endothelium of the capillaries in the lamina propria and migrate into the stroma. This is thought to augment uterine defenses during breeding. Also seen in this image are some marginating eosiniphils (E). They are commonly seen in the stroma of equine endometrial biopsies and although they have been associated with the "wind-sucking" condition, this is poorly substantiated.

The capillary containing these cells is surrounded by endometrial glands with lumens that are not obvious.

The image below shows the typical appearance of lumen epithelial cells during estrus. They are significantly taller than the same cells epithelial cells during diestrus (the luteal phase). Also note the cilia. They are dispersed intermittently across the surface of the epithelium. On a scanning electron micrograph they appear like tufts of  grass on a barren lawn. Between the "tufts of grass" are the intermittent openings of endometrial glands.

Image size: 990 x 630px

Hemosiderin is commonly found in macrophages in endometrial biopsies. Evidence of this is shown below. The presence of hemosiderin, which usually remains in the endometrium for long periods of time, usually reveals that a mare has experienced intrauterine hemorrhage sometime in her life. Although there is practically no overt hemorrhage from the endometrium during or after foaling, mild hemorrhage is likely. Therefore endometrial hemosiderosis probably indicates that a mare has had one or more foals in her lifetime.

Image size: 990 x 603px

Plasmacytes  and lymphocytes are common "janitorial cells" in the lamina propria, especially the stratum compactum as shown below. On occasion, even highly experienced pathologists may have difficulty distinguishing between these two types of cells. They provide local immunity in the endometrium and unless they are present in large numbers should not be interpreted as an indication of chronic endometritis.

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A uterine biopsy

Keywords: uterine, uterus, biopsy, infertility, punch

Endometrial biopsies are important in diagnosing endometritis and other causes of infertility in mares.

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The jaws of a biopsy instrument are shown here on the dorsal endometrial surface where biopsies on normally taken. This is because the biopsy instrument is placed in the uterus and the dorsal endometrium is pushed down (per rectum) into the jaws of the punch. Sometimes this is referred to as a "guided" biopsy technique. It is far superior to a "blind" biopsy technique where the endometrial biopsy punch is inserted through the cervix and its jaws are closed in the hope of obtaining a satisfactory biopsy.  This author has read endometrial biopsies for a diagnostic laboratory for many years and most of the unsatisfactory samples were taken using the "blind" technique. In fact, samples of the cervix have often been submitted instead of endometrial biopsies.

When taking a biopsy, It is safer to feed the endometrium into the side of the jaws as shown here rather than into the front of the jaws. A large, deep and penetrating biopsy can result in the latter case. This instrument is made by the Pilling company, USA.

The inset shows the biopsy itself being deposited into a container of Bouin's fluid which is 80% picric acid and 20% formalin.  This is a so-called "hard fixative" suitable for genital and embryonic tissue because the histological architecture is not destroyed when the large amounts of water in these tissues are extracted during processing.  However, the use of Bouin's fluid is by no means mandatory because ordinary formalin also provides satisfactory results.

Endometrial biopsy site; four days post biopsy

Keywords: endometrium, mare, equine, biopsy, uterus

Image size: 1094 x 778px

The site of an endometrial biopsy in a mare, four days after the procedure; a normal situation.

The endometrium in this case was devoid of inflammation and the site of biopsy was already difficult to identify macroscopically. Although a small amount of hemorrhage usually occurs at the site of biopsy, even 24 hours later it has healed well enough to allow insemination. Therefore, should the need arise, an endometrial biopsy can be taken during the estrous period during which breeding is planned.

Endometrial cup formation

Keywords: equine, mare, eCG, endometrial, cups, uterus, abortion

Image size: 1500 x 1126px

Endometrial cup formation at about 45 days of gestation. The fetus has been removed from its placenta and placed on the endometrial cups as a source of reference.

A section of the endometrial cup/s is indicated here by the green arrows. In this authors opinion, the term "cup" is misleading because these structures are only cupped in cross section but otherwise bear no resemblance to cups. In fact, as is seen here, the cups are often elongated and some cups coalesce with others. They are irregular in shape and vary greatly in size within a single pregnancy.

The cups are actually of fetal origin, producing eCG, formally called pregnant mare serum gonadotropin or PMSG. Equine chorionic gonadotropin production usually starts at about 28 to 35 days of gestation and continues to about 120 days of gestation, sometimes longer and on rare occasions, throughout pregnancy.

The function of eCG is an enigma (2013) because it is associated with multiple ovulation during pregnancy yet cannot induce superovulation in non-pregnant mares. Also, as seen here, most mares have multiple ovulations, forming accessory corpora lutea while eCG is being produced. Yet, a minority have normal pregnancies with no accessory corpora lutea.

A further intriguing finding is that the production of eCG persists after abortion and in most cases usually causes prolonged anestrus. There is no easy and effective method for shortening the life of endometrial cups once they have formed therefore it is advisable to perform therapeutic abortions before day 28, when endometrial cups begin to form. However this situation requires clarification because recent reports on polo ponies challenge these assertions. In polo ponies male pregnancies are often aborted after fetal sexing at about 60 days yet many of those mares have estrous cycles after abortion.

Selected reference:

Estrade, M.J. et al. 2016 eCG Concentration and subsequent reproductive activity in mares after abortion at day 70. J.Equine Vet.Sci. 42:88-93