Equine
Reproduction
Dr.
Jack Sales, DVM
CopyrightÓ2004
Lesson 7
Fetal
Development, Abortion,
Induced Parturition and Dystocia in the Mare
Assignment: Read Chapter 8 & 10 in
the text.
In this lesson we
will revisit specific embryonic and fetal ages that are significant in the
overall management concerns of a breeding farm. These time periods should be
committed to memory. They are listed as
items A through K under I, below.
I.
Normal fetal development in the mare
A. Fertilization of ovum (egg) occurs in the oviduct
(fallopian tube) of the mare.
B. Fertilized ovum transported into the horn of the uterus at
5 to 6 days.
C. Recovery of embryo at 7 days for embryo transfer is 64 to
128 cells.
D. Day 14 embryo prevents release of prostaglandin and can be
detected by ultrasound as a pregnancy.
E. If twinning has occurred, pinching off one vesicle (embryo)
is attempted at approximately day 18 when the embryo has fixed in location.
F. Endometrial Cups form by day 45 and release progesterone
for pregnancy maintenance until day 120.
G. By day 60 the fetus has the unmistakable appearance of an
equine.
H. By days 150 to 160 ears will appear fully developed. Ergots
will appear.
I. By 220 days development of mane and tail; the weight will
be 8 to 10 kilograms (22 lbs).
J. By day 300 the fetus will have a full hair coat; the weight
will be 20 Kilos (44 lbs).
K. By 340 days the weight will reach 45 to 50 kilos (100 lbs).
II.
Abortion in the mare (spontaneous
loss of pregnancy before term – miscarriage)
A.
Early embryonic death – death and resorption of embryo prior to 40
days pregnancy is very commonly seen on
breeding farm (12%
occurrence).
1. Twinning will often cause a mare to abort at anytime during
pregnancy.
a.
Light breed mares rarely carry twins to term.
2. Infectious causes of abortion.
a. Equine Rhinopneumonitis virus
1.
Can be vaccinated to prevent abortion (pneumabort
vaccine – 5th , 7th and 9th
month of pregnancy).
B. Equine Arteritis
1. Not as common as Rhino (presently eradicated from major
breeding states).
2. Vaccine available.
C.
Bacterial causes of abortion.
1. The same bacteria that cause endometritis.
Infection is
not cleared and mare becomes pregnant.
Fetus
becomes infected in the womb, dies and is aborted.
On occasion it is
considered necessary or at least helpful if a mare can be induced to foal at a
specific time. When induction of foaling is contemplated it is very important
to follow certain guidelines in order to prevent possible complications that
may lead to the death of the mare or foal. The following guidelines should be
kept in mind when considering induction.
III.
Induced parturition
A. Mare must be at full term and show all signs of impending
foaling.
1. Musculature relaxation of croup, buttocks and
perineum.
2. Waxing or milk from the udder.
B. Veterinarian must be involved.
1. Check for cervix relaxation of dilation.
2. Check for correct positioning of the foal.
C. Procedure.
1. Mare is prepared for foaling (tail wrapped
and cleaned).
2. Mare is administered Oxytocin (3½ cc)
intramuscularly.
3. Mare will begin first stage of labor within
10 to 15 minutes
and continue through the normal foaling
process.
Induction of parturition can occasionally be accompanied by
complications, so attendance by veterinarian is crucial.
IV.
Problems involving normal
delivery.
The following should
supplement your text reading and can be used as a study guide for common
foaling problems that may be encountered.
A. Red Bag Delivery
(premature placental detachment).
If
reddish membrane appears before the foal appears, it is an emergency
and the bag must be torn opened and the foal must be pulled as quickly as
possible (the blood supply to the foal is separating to early).
Red Bag Delivery
B. Dystocia – Difficulty in foaling usually do
to malposition of foal.
1. Breech birth – hind legs come first – not commonly
seen – you must deliver foal as soon as possible (cord may break before the
head is cleared from passage, preventing normal breathing).
2. There are many other types of malposition of
foal, some can easily be corrected and some may require cesarean section.
If foal is not delivered within 30 to 40
minutes of the beginning of the second stage of labor (after the water breaks)
there will be a much greater chance the foal will be born dead.
C. Uterine Torsion
1.
This is a twisting of the uterus in the cervix area, and can
occur anytime during the last few months of
pregnancy.
2.
Veterinary attention is necessary as soon as possible,
sometimes surgery is indicated.
D. Uterine Prolapse
1.
This occurs shortly after the foals is born. Uterine
contractions to expel the afterbirth may
cause the
uterus to prolapse or come out of the
abdominal cavity.
2.
This is an emergency requiring veterinary assistance
as soon as possible.
E. Uterine Rupture
1.
Mare will stop passing foal and go into shock.
You should
pull the foal; if already partially passed
(head is out) the foal
will probably survive.
This is an emergency that requires
immediate
veterinary assistance;
the mare may not survive.
F. Ruptured Uterine Artery
1.
Mare usually bleeds out within 5 to 10 minutes causing
death.
2.
Most often seen in older mares (over 15 years of age).
V.
Complications in mare following
delivery.
A. Internal
hemorrhage.
1. Uterine bleeding can
be severe or mild.
a. Vaginal lacerations – seen with large
foals.
b. Cervical lacerations – usually
cause minimal
bleeding.
B. Retained Placenta.
1. Considered retained after 3 hours.
2. Do not pull on afterbirth; do not tear
afterbirth.
a. Requires veterinary assistance.
1. Oxytocin injection to stimulate uterine contraction.
2. Intrauterine antibiotic infusions.
3. Infection caused by even small pieces of afterbirth can
cause shock and founder in the mare.
C.
Cramping or signs of colic after foaling.
1. Usually due to
uterine contractions post foaling.
2. Banamine or
has already
passed her afterbirth (will inhibit uterine
contractions).
3. Some post foaling mares are more apt to have
impactions
post foaling.
Mineral oil given by the veterinarian would be
indicated
D. Perineal
Lacerations
1. Normally caused by large foal.
2. Normally should be immediately attended to by
veterinarian
(sutured).
E. Rectovaginal lacerations
1. Caused by foals foot being driven through the
vaginal
wall into the
rectum during a
uterine contraction while
foaling.
2. May just leave a hole through this area if
foals foot
is replaced before more
contractions occur
F. Third degree RV laceration refers to the
shelf between the
rectum and vagina
being completely torn out.
1. This is not
normally an emergency.
2. Veterinarian usually not able to suture the
laceration
immediately due
to the extensive bruising of the tissues.
3. Mare is put on antibiotics, given a tetanus
injection,
given pain
medication and allowed to heal as is for
about 3 weeks to 2 months before
veterinarian will
consider
stitching the area.
4. Must keep mare as clean as possible and treat
the
wound
regularly for optimum healing.
5. The surgery to stitch this area is done in
the standing
position
normally under local anesthetic.
Ruptured
pre-pubic tendon – can occur in the third trimester of
pregnancy or just before
foaling.