Group Title: Acta Veterinaria Scandinavica 2007, 49 (Suppl 1): S9
Title: High risk pregnant mare
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Title: High risk pregnant mare
Series Title: Acta Veterinaria Scandinavica 2007, 49 (Suppl 1): S9
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Creator: Troedsson MHT
Publication Date: 12/12/2007
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High risk pregnant mare
Mats HT Troedsson


Address: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, 32610-0136, USA
Email: Mats HT Troedsson troedssonm@vetmed.ufl.edu



from Perinatal Death In Domestic Animals: The 20th Symposium of the Nordic Committee for Veterinary Scientific Cooperation (NKVet)
Reykjavik, Iceland. 26-27 April 2007

Published: 12 December 2007
Acto Veterinaria Scandinavica 2007, 49(Suppl I):S9 doi:10.1 186/1751-0147-49-S I-S9


This abstract is available from: http://www.actavetscand.com/content/49/S I/S9
2007 Troedsson; licensee BioMed Central Ltd.


Introduction
Improved diagnostic techniques and advances in the
understanding of equine reproductive physiology and
pathology have resulted in increased pregnancy rates in
mares. In contrast, the incidence of pregnancy loss has
remained fairly constant at a rate of 10-15% [1]. Preg-
nancy losses during late gestation (>5 months) represent
an even greater problem for the equine breeding industry.
Affected mares will not only fail to produce a foal, but will
often have a lower conception rate during the next breed-
ing season.

Pregnancy losses during late gestation could be the result
of fetal illness, placental dysfunction, or maternal illness
(see Table 1). Pre-partum disorders of the mare are easy to
diagnose, but identifying conditions that affects the fetus
and the placenta may be more difficult. Monitoring of the
fetus and the placenta during late gestation is routinely
performed in human pregnancies, but has only recently
gained recognition in equine veterinary medicine.

Fetal evaluation
Indications for examination of the fetus include early lac-
tation, vaginal discharge, maternal systemic illness, larger
than normal abdominal size, suspected twinning, over-
due pregnancy and a previous poor outcome of parturi-
tion [2-5].

Transabdominal ultrasonography of the equine fetus can
be performed reliably after 90 days of gestation. At this
time, the uterus drops over the pelvic brim and is visible
from the ventral abdomen. The assessment of fetal well
being is obtained through measurement of heart rate, size,


movement and tone of the fetus. The thickness of the fetal
membranes, echogenicity and quantity of the allantoic
and amniotic fluids, and the number of fetuses provide
information to evaluate the fetus.

The fetus is visible in the inguinal area and between the
mammary glands in early gestation [5]. As pregnancy
progresses the fetus is found progressively more cranial. It
is necessary to apply alcohol or to clip the hair on the
abdomen to obtain a diagnostic image of the fetus. In late
gestation, the mare should be examined from the mam-
mary glands to the xyphoid extending to the level of the
stifles on both sides of the abdomen.

Variable gestational length, size and body type of the mare
and position of the fetus will affect the choice of trans-
ducer. The highest frequency transducer that will pene-
trate to the desired depth should be chosen. Generally a
2.5 or 3.5 MHz transducer is required to image the fetal
heart in late gestation since a depth of 30 cm is often
required [5,6]. A second higher frequency transducer
(7.5-10 MHz) should be used to image the uteroplacental
unit [6]. Either a curvilinear or sector scanner is preferred
because they produce a pie-shaped image that allows an
increasingly larger field of view in the deeper section of
the image. Sedation of the mare will affect the heart rate,
tone and movement of the fetus and should be avoided if
possible. The ventral abdomen of the mare should be
scanned in the sagittal and transverse plane.

The entire uterus should be scanned to determine the
number of fetuses and the position of the fetus. The fetus
should be lying in the sagittal plane in cranial position


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Table I: Conditions causing high risk pregnancies


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Maternal conditions

Colic
Endotoxemia
Abdominal tunic rupture
Prepubic tendon rupture
Dystocia
Uterine inadequacy
Uterine torsion
Hyperlipemia


Fetal conditions

Twins
Dystocia
Congential defects
Hydrops


Placental conditions

Placentitis
Twisted umbilical cord
Fescue toxicity


[5,6]. In late gestation the head of the fetus is near the
brim of the pelvis. Orbital diameter can usually only be
obtained by transrectal scanning [7,8]. The fetus is in dor-
sal recumbency with the vertebrae closest to the ventral
abdominal wall [6]. To determine fetal orientation, the
uterus should be scanned in a sagittal section. The thorax
of the fetus can be localized by the recognizable striped
pattern (see Figure 1). The heart is found in the cranial
aspect of the thorax. The fetal heart rate has been sug-
gested to be used as an indicator of fetal well being [9]. A
poor outcome of parturition was associated with brady-
cardia or tachycardia in the fetus. Heart rate of the fetus
peaks at 3 months of gestation to a mean of 196 beats per
minute and then gradually decrease throughout preg-
nancy [10]. The decrease in fetal heart rate is a result of
increasing parasympathetic tone to the heart [2]. The aver-
age fetal heart rate in a fetus greater than 300 days gesta-
tion is 75 + 7 bpm [9]. Fetal heart rate slows by
approximately 10 bpm at greater than 330 days gestation.


Figure I
Transabdominal ultrasound image of the fetal thorax
obtained with a 2.5 MHz sector scanner transducer.
The shadows are caused by the vertebrae and ribs. Ventral is
the top of the image and dorsal is at the bottom.


Fetal heart rates vary with activity level which should be
considered when examining a mare. Consistently low or
high fetal heart rates are associated with fetal stress. Serial
examinations should be performed to verify fetal well
being or distress. Mares considered "at risk" for pregnancy
loss are often examined on a daily basis. Fetuses experi-
encing distress are often evaluated several times a day.
This is particularly true when determining if fetal distress
is significant enough to prompt intervention such as
induction of parturition.

Fetal heart rate can be obtained either by using a stop-
watch while monitoring the B mode image or utilizing M-
mode. M-mode displays movement at a fixed position of
the transducer. The M-mode cursor is moved so that it
intersects the heart. The M mode image is activated. The
image displayed will show movement of the heart over
time (see Figure 2). The heart rate is automatically calcu-
lated by measuring the time between 2 cardiac cycles. M-
mode analysis is more accurate in assessing the fetal heart
rate than the stopwatch method.

Aortic diameter has been shown to correlate to maternal
weight and is a good indicator of fetal size during late ges-
tation [6]. The aorta is visualized as it exits the heart and
courses dorsally in the fetus adjacent to the vertebrae. The
aorta is measured at the caudal border of the heart. Nor-
mal aortic diameter obtained in 32 light breeds of mares
with normal pregnancies ranged from 18.5-27 mm [6]. A
smaller than normal aortic diameter has been associated
with abnormal foals with low birth weight [10]. Fetal tone
should be present. A flaccid fetus that floats in the fluids
is an indication of a weak or dead fetus. The normal
healthy fetus should exhibit movement during the ultra-
sound scan. Movement may be extension or flexion of the
limbs or rotation on the fetal long axis [5,6]. As the fetus
ages, it will display more complex movements [3].

The amniotic membrane is seen as a thin hyperechoic
structure floating within the fetal fluids. The membrane is
thin in the normal pregnancy although cysts may be seen
[3]. In regions of the uterus where the foal is making con-
tact with the uteroplacental unit the amnion is rarely dis-


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Figure 2
Transabdominal ultrasound image of the fetal heart
obtained with a 2.5 MHz curvilinear scanner trans-
ducer. The B-mode image is at the left of the picture. The
M-mode image is at the right of the picture. The cursor
marks delineate two cardiac cycles. The calculated heart rate
is 100 bpm.


cemable. The amount of fetal fluids should be assessed in
4 areas within the uterus (right and left cranial and cau-
dal). Generally the largest fluid depths are located around
the fetal thorax in the region of the elbow (see Figure 3)
[6]. The depth of the allantoic and amniotic fluids is used
to assess total volume of fetal fluids. The normal mean for
maximal allantoic and amniotic fluids is 13.4 + 4.4 cm
and 7.9 + 3.5 cm, respectively. The allantoic and amniotic
fluids should contain a moderate amount of particles.
Echogenic free-floating particles are normal from month
4 to the end of gestation [6,11]. The hippomane may be
seen floating within the allantoic fluid. It has an oblong
shape with a layered or onion appearance to the more
echogenic center.

Evaluation of mammary secretion to assess fetal maturity
Measurement of the concentration of sodium, potassium
and calcium in mammary secretions of mares before foal-
ing can provide information about impending foaling
and fetal maturity [121. In the late pregnant mare, the elec-
trolytes are reflecting concentrations in serum. Between 2
and 3 days before parturition, the sodium concentrations
in mammary secretion decline and the potassium concen-
trations rise, resulting in an inversion of the electrolyte
concentrations. In addition, the calcium concentrations in
mammary secretion increase within a day before parturi-
tion. Analysis of milk electrolytes in high risk pregnant
mares can be helpful in providing information on fetal
maturity. Occationally, an inversion of sodium and potas-


Figure 3
Transabdominal ultrasound image of the allantoic
and amnionic fluid pockets obtained with a 5.0 MHz
curvilinear transducer. The amnionic membrane divides
the 2 pockets (arrow).


sium milk concentrations may occur prior to fetal matu-
rity. It is therefore important to use mammary secretion
electrolyte data in conjunction with gestational length
and other clinical data.

Placental evaluation
The equine placenta consists of the allantochorion, the
allantoamnion, and the umbilical cord. The chorionic
part of the allantochorion is attached to the endometrium
through microcotyledons, which integrate the
endometrium throughout the uterus with exception of a
small area at the internal os of the cervix, the so-called cer-
vical star. The allantochorion supports the fetus in utero.
It provides respiratory and nutrient exchange between the
mare and the fetus, and it is an endocrine active organ
with hormone synthesis and metabolism of importance
for maintenance and normal development of the fetus.
The "free floating" allantoamnion allows the fetus to
move freely within the uterus. It is not attached to the
allantochorion with exception of a small area at the
umbilical stalk. The only attachment between the fetus
and the allantoamnion is at the umbilicus. The umbilical
cord has an amniotic portion and an allantoic portion.
The umbilicus contains two umbilical arteries, one umbil-
ical vein, and the urachus. The length of the cord, and the
length of the allantoic and amniotic portions can vary, but
is normally 50 to 100 cm long. A cord length of >80 cm
has been reported to predispose to abnormal twisting of
the cord and fetal death [13].

Evaluation of the equine placenta is routinely performed
after parturition. A thorough examination of the placenta
post partum provides valuable information on disease


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processes or dysfunctions that could have affected the well
being of an aborted fetus, or potentially cause illness in
the neonatal foal. However, this examination does not aid
the clinician in decisions that are aimed to prevent abor-
tion or neonatal diseases of the foal. Evaluation of the pla-
centa in the mare can be performed by the use of
ultrasonography and endocrine tests.

Ultrasonographic evaluation of the placenta
Transabdominal ultrasonography
Ultrasonographic examinations of the placenta in mares
that are considered to be at risk for abortion during late
gestation are routinely performed by a transabdominal
approach [10,14,15]. Using a 5-7.5 MHz transducer, nor-
mal values for the combined thickness of the uterus and
the placenta (CTUP) has been established (see Figure 4)
[10,11,14]. Reef and co-workers recommended to exam-
ine four quadrants of the placenta; right cranial, right cau-
dal, left cranial, and left caudal [6]. Using this technique,
they suggested that mares with normal pregnancies
should have a minimal CTUP of 7.1 1.6 mm, and a max-
imum CTUP of 11.5 2.4 mm. In a subsequent study, it
was observed that mares with an increased CTUP often
delivered abnormal foals [10]. A CTUP of >17.5 mm has
been suggested to be consistent with placentitis [16].
Renaudin et al, examined the monthly variations of the
CTUP in mares with normal pregnancies [11]. Their study
confirmed previous studies, but showed a significant dif-
ference in the CTUP between pregnancy months. How-
ever, the CTUP did not increase consistently, and the
reliability of measuring CTUP by a transabdominal
approach was questioned. Nevertheless, placental thick-
ening and partial separation of the allantochorion from
the endometrium may be observed by the use of transab-
dominal ultrasonography in mares with placentitis origi-
nating from hematogenous infection (see Figure 5). In
addition, a pocket of hyperechoic fluid can be seen at the
base of the lowest area of the uterus in mares with the
Nocardia form of placentitis [17,18].

Mares grazing endophyte-infected fescue often experience
premature separation of the allantochorion, increased
allantochorion weight and thickness, and retained pla-
centa. A significant increase in uteroplacental thickness
and premature separation of the allantochorion has been
demonstrated on transabdominal ultrasonographic
examination of endophyte-infected mares. However, the
thickness was not observed until an average of 8 hours
before the onset of labor [19].

Transrectal ultrasonography
Although a transabdominal approach provides excellent
image of the fetus and most of the uterus and placenta, the
caudal portion of the allantochorion cannot be imaged by
this approach, resulting in difficulties to diagnose early


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Figure 4
Transabdominal ultrasound image of the uteropla-
cental unit in a normal mare at 320 days of gestation.
The image was obtained with a 7.5 MHz curvilinear array
transducer. The X marks the thickness of the uteroplacental
unit.


stages of ascending placentitis. However, transrectal ultra-
sonography of the caudal allantochorion in late gesta-
tional mares provides an excellent image of the placenta
close to the cervical star (see Figure 6). Renaudin et al,
examined normal pregnant mares monthly during gesta-
tion, starting at 4 months of pregnancy until parturition
[11]. A 5-7.5 MHz linear transducer should be positioned
1-2 inches cranial of the cervical-placental junction, and
then moved laterally until a uterine vessel is visible at the
ventral aspect of the uterine body [11]. The CTUP should
then be measured between the vessel and the allantoic
fluid (see Figure 6). It is important to obtain all CTUP
measurements from the ventral aspect of the uterine body,
since physiological edema of the dorsal aspect of the
allantochorion has been noted in normal pregnant mares
(see Figure 6) [11]. In addition, care should be exercised
to be certain that the amniotic membrane is not adjacent
to the allantochorion, since this may result in a false
increased CTUP. When possible, three measurements
should be taken and averaged. Normal values for CTUP
have been established (see Table 2) [11,20]. Increases in
CTUP have been associated with placental failure and
pending abortion [20,21] In some cases of placentitis,
hyperechoic fluid (purulent material) can be noticed sep-
arating the uterus and the placenta. Measurements in
these cases are meaningless as one is no longer measuring
the combined unit.

Additional parameters that can be evaluated using tran-
srectal ultrasonography include changes in the amniotic


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Figure 5
Transabdominal ultrasonography of the placenta in a
mare during 9th month of gestation. The arrow points
to the area of placental separation.


membrane and fluid character. Amniotic thickening,
which occurs in some cases of placentitis, can be identi-
fled using transrectal ultrasonography. Changes in allan-
toic and amniotic fluid character can also be identified
using transrectal ultrasonography. In normal mares, allan-
toic fluid is commonly hypoechoic with some specular


Figure 6
Transrectal ultrasonography of the caudal part of the
placenta in a late gestational mare. A = amniotic mem-
brane; B = uterine blood vessel; x---x = CTUP.



material, while amniotic fluid is frequently a shade more


hyperechoic (gray) than allantoic fluid [11,14]. Marked
changes in these fluid characteristics suggest placental
infection or stress to the fetus.

While transrectal and transabdominal ultrasonographic
examination of the placenta is useful to detect early signs
of some placental pathology, it is important to keep in
mind that placental changes resulting in periparturian
problems can be subtle and may not readily be detected
on ultrasonographic examination. For example, a correla-
tion between both endometrial fibrosis and angiosis, and
poor chorionic villous development has been reported
[22,23]. These changes can of course not be evaluated by
the use ofultrasonography, but would require other tech-
niques.

Endocrine monitoring of the placenta
Progesterone
The equine placenta is part of an endocrine fetal-placental
interaction, which synthesizes and metabolizes progesta-
gens [24] This endocrine function of the placenta is
important for maintenance of pregnancy after the
endometrial cups and the secondary corpora lutea disap-
pear around day 120 150 of gestation. Fetal-placental
progesterone is rapidly metabolized to 5a-pregnanes.
Mares with placental pathology may have increased
plasma concentrations of progestagens as a result of stress
to the fetal placental unit [25]. Unfortunately, 5a-preg-
nanes are not readily assayed in a commercial setting, so
diagnosis of placental disease using 5a-pregnane concen-
trations is not possible. There is cross-reactivity between
5a-pregnanes and progesterone using some commercial
radioimmunoassays for progesterone. In recent studies
[26,27] using an experimental model to induce placenti-
tis, it was found that mares that develop a chronic form of
placentitis responded with increased plasma progesterone
concentrations. Conversely, mares that developed acute
placentitis and abortion soon after infection experienced
a rapid drop in plasma progesterone concentrations. It
was suggested that measurement of repeated samples of
plasma progestin concentrations in mares with placentitis
might be a useful method to identify mares that may abort
or deliver prematurely [26]. Furthermore, sensitivity of
progesterone assays can be improved when combined
with evidence of placental thickening as detected using
transrectal ultrasonography [27].

Estrogen
Estrone sulfate in maternal serum has been used to mon-
itor fetal well being [28]. However, this test has not con-
sistently been useful to detect early signs of placentitis
[29].


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Table 2: Normal upper limits for the combined thickness of the
uterus and the placenta (CTUP) during late gestation [II, 20].

Gestation length Normal CTUP

151 270 days <7 mm
271 300 days <8 mm
301 330 days <10 mm
331 <12 mm


Relaxin
Relaxin is produced by the equine placenta, and can be
detected in peripheral blood plasma from day 80 of gesta-
tion and throughout the pregnancy [30]. The role of
relaxin during pregnancy is not fully understood, but
there is some evidence that placental relaxin production is
compromised in mares at risk of aborting their fetuses
[31,32]. Ryan and co-workers observed subnormal
plasma relaxin concentrations in mares with abnormal
pregnancies [32]. Mares with clinical signs of placentitis
and mares exhibiting signs of fescue toxicosis had sup-
pressed plasma relaxin concentrations. There is currently
no commercial test available for equine relaxin, and more
research need to be performed to evaluate the usefulness
of plasma relaxin as a clinical tool to diagnose placentitis
and to monitor the efficacy of treatment strategies.

Management and treatment of high risk mares
General considerations
High risk pregnant mares should be monitored for fetal
and placental well-being. Progestin therapy is currently
being implemented in humans to halt preterm labor. Pre-
sumably, the anti-prostaglandin effect of progestins con-
tribute to reduced myometrial activity by interfering with
upregulation of prostaglandin and oxytocin receptors
[33]. Without receptor formation, gap junction formation
would be inhibited and uterine contractility prevented.
Treatment with progestins has long been advocated to
promote uterine quiescence in mares with uterine pathol-
ogy. Daels and co-workers showed that supplementation
of mares with the synthetic progestin altrenogest (0.088
mg/kg SID) was able to prevent prostaglandin-induced
abortion [34].

A variety of tocolytic agents have been used in women
with preterm labor including: magnesium sulfate, P sym-
pathomimetic agents (ritodrine, terbutaline), prostaglan-
din synthesis inhibitors (indomethacin, suldinac,
ibuprofen, aspirin), calcium channel blockers (nifed-
ipine) and oxytocin antagonists (atosiban) [35] Tocolytic
agents have not been shown to significantly prolong preg-
nancy or improve neonatal outcome when used alone.
Historically, tocolytics prolong pregnancy for up to 48
hours during which time glucocorticoids can be adminis-
tered to the mother in an effort to expedite fetal matura-


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tion. Clenbuterol, a P sympathomimetic agent, has been
used in clinical equine practice. The effects of clenbuterol
administration on uterine tone and maternal and fetal
heart rates were examined by Card and Wood [36]. Clen-
buterol was administered intravenously (300 gg) to four
pregnant mares throughout gestation until parturition.
Uterine relaxation occurred within 3 minutes of drug
administration and persisted up to 120 minutes. The
authors concluded that clenbuterol was effective in caus-
ing uterine relaxation throughout gestation, and that the
side effects were minimal and transient. A more recent
study reported the effects of clenbuterol when adminis-
tered to 29 mares late in gestation [37]. These authors con-
cluded that clenbuterol was not effective in preventing the
onset of myometrial contractions in normal foaling mares
at term. Treated mares in this study actually foaled earlier
in the evening than untreated mares. The authors specu-
lated that the relaxant effects of clenbuterol may have pro-
moted cervical relaxation and subsequent parturition.
Based on side effects detected when clenbuterol is admin-
istered to pregnant mares, and lack of effect for delaying
normal parturition, the authors suggest that this agent has
limited usefulness in horses.

Management of selected high risk pregnancy conditions
Colic
The risk of postoperative abortion in mares undergoing
surgery for colic is surprisingly low, and not related to
stage of gestation or type of lesion. In a retrospective
study, Santschi and co-workers found that 18% of surviv-
ing mares that underwent colic surgery experienced preg-
nancy loss [38]. Half of the abortions occurred long after
the resolution of the disease, and may have been unre-
lated to the surgery or colic. Hypoxia and endotoxemia
were identified as risk factors associated with death of the
fetus. Abortions were associated with a PaO2 <80 mm Hg
when surgery occurred during the last two months of ges-
tation.

Uterine torsion usually presents as a mild colic during the
last trimester of pregnancy. Diagnosis is based primarily
on rectal palpation of the broad ligaments. When the
uterus is torsed, the mare is at risk for uterine rupture.
Options for correction include rolling the mare, or surgi-
cal correction. Rolling may be an alternative to surgery
early in the third trimester, but should not be tried in
mares close to term due to increased risk of uterine rup-
ture. Surgical correction is the most effective treatment for
uterine torsion, and was found to result in the highest sur-
vival rate of foals [39]. Furthermore, the prognosis for
mares and foals is best when uterine torsion occurs at
<320 days of gestation [391.


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Abdominal tunic and prepubic tendon rupture
Ruptures of the abdominal tunic or prepubic tendon are
painful and result in varying degree of edema of the ven-
tral abdomen. Mares with a rupture of the prepubic ten-
don have an abnormal position of the pelvis and
mammary glands. The tuber coxae is tipped up and the
tuber ischii tipped down. The mammary gland is dis-
placed because of the loss of caudal attachment of the
abdominal wall [40]. The prognosis for mare and foal is
poor in mares with a complete rupture. Stall confinement,
anti-inflammatory drugs, and abdominal support should
be implemented. The progression of the condition of
abdominal muscle and tendon, and the fetal well-being
should be monitored by ultrasonography. Parturition
should be induced and attended when the fetus is ready
for birth. Measurement of milk secretion electrolytes are
helpful in determining when it is safe to induce parturi-
tion.

Hydrops
Hydrops is the accumulation of excessive fluid within the
amniotic or allantoic cavity. The condition is uncommon
in mares, and the prognosis for pregnancy is considered
poor. Presenting signs include a history of rapid abdomi-
nal enlargement over 10-14 days after the 7th month of
gestation. Mares will be depressed and uncomfortable
with labored breathing, ventral edema, and possibly diffi-
culty walking. Risk of uterine rupture, abdominal hernia,
or prepubic tendon rupture are all increased. To save the
mare, termination of the pregnancy is often recom-
mended. However, sudden removal of abdominal fluid
associated with termination of the pregnancy or foaling
may result in blood pooling in the abdominal vascula-
ture, leading to hypovolemic shock and death of the mare.
Therefore supportive fluid therapy is needed at the time of
foaling or termination of pregnancy to maintain blood
pressure. If possible, fluid should be drained gradually
prior to removing the fetus. A case of successful manage-
ment of a mare with hydrops amnion, resulting in the
birth of a live foal was recently reported from the Univer-
sity of Florida Veterinary Medical Center [41]. The mare
was closely monitored for integrity of the abdominal wall,
degree of abdominal extension, and the abdomen was
supported with a girdle-like device. The pregnancy was
supported medically to prevent preterm labor, and the
mare produced a live foal at a normal gestational time.

Placentitis
Placentitis in mares poses a significant threat to fetal and
neonatal viability. Placentitis is commonly caused by bac-
teria ascending through the vagina. The most frequent
bacterial pathogens implicated in equine placentitis are
Streptococcus equi subspecies zooepidemicus, Escherichia coli,
Klebsiella pneumonia, and Pseudomonas aeruginosa [42].
While bacterial infection initiates disease, recent work


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from an experimental model of ascending placentitis in
pony mares showed that premature delivery may occur
secondary to inflammation of the chorion rather than as
a consequence of fetal infection [43,44]. It was suggested
that these inflammatory processes may result in prostag-
landin production (PGE2 and PGF2a) and stimulation of
myometrial contractility, thus resulting in preterm deliv-
ery. However, in some chronic cases of placentitis, foals
will experience accelerated fetal maturation. These foals
will be delivered prematurely, but will be mature enough
to survive in the extrauterine environment. In humans, it
is thought that indirect stimulation of the fetal hypotha-
lamic-pituitary-adrenal axis by pro-inflammatory
cytokines is responsible for precocious fetal maturation
[45,46]. If this phenomenon is also true for equine
fetuses, then delaying premature labor long enough to
allow accelerated fetal maturation to occur may improve
foal survival rates. To achieve this goal, it is necessary to
promptly diagnose and effectively treat the disease. The
most common signs of placentitis in mares are premature
udder development ( streaming of milk) and vulvar dis-
charge. Transrectal and transabdominal ultrasound, com-
bined with endocrinological assays, provide additional
tools for early diagnosing and monitoring progression of
placentitis in mares. Pregnant mares with signs of placen-
titis should be treated with systemic broad spectrum anti-
biotics and anti-inflammatories. Using in vivo
microdialysis to detect concentrations of commonly used
drugs in allantoic fluid of pregnant pony mares, Macpher-
son and co-workers at the University of Florida found that
penicillin (22,000 IU/kg, q 6 h), gentamicin (6.6 mg/kg,
q 24 h) and trimethoprim sulfamethoxazole (30 mg/kg,
BID) resulted in inhibitory concentrations (MIC) of these
drugs in allantoic fluid and placental tissue [47,48]. Pre-
liminary experimental data and clinical observations sug-
gest that long term therapy with a combination of
antibiotics, altrenogest (regumate; 0.088 mg/kg), flunixin
meglumine (1.1 mg/kg BID), and pentoxifylline (8.4 mg/
kg BID) can positively impact pregnancy outcome with
delivery of healthy foals in mares with placentitis [49].

Acknowledgements
Portions of this article are adapted from Troedsson M and Sage AM. Fetal/
Placental Evaluation in the Mare. In: Ball B.A. (Ed.), Recent Advances in Equine
Reproduction. Ithaca: International Veterinary Information Service http://
www.ivis.org, 2001; Document No. A0203.0501.

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