Equine
Reproduction
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. This material does not prepare the student for
dealing with foaling problems without the attendance of a veterinarian. Time is of the essence when the mare is in
distress – call the vet immediately.
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 open and the foal must be pulled as quickly as
possible (the blood supply to the foal is separating too early). Those attending the mare must act quickly –
in this instance waiting for the veterinarian will ensure death of the foal –
be prepared.
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.
ASSIGNMENT:
Please send to jsales@horsecoursesonline.com "Lesson 7 Repro" in subject
line.
1. In your own
words outline the fetal development of the foal from conception to birth.
2. List signs of embryonic loss in the mare and
discuss methods that can be used to confirm it.
3. What control
procedures can be used for those causes of abortion listed in question 2?
4. Describe 5 of
the more common foaling and post foaling complications and a brief description
of proper handling.
5. Give at least 3
reasons why twins should not be allowed to go to full term.