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Unit 3
Life Cycle Considerations --
Parturition
Parturition is
the act or process of giving birth to offspring. The terms used to describe
parturition vary with the species of animal it is being used to describe. The
following are examples of parturition terminology:
A number of physical, physiological and hormonal changes take place
to prepare the dam and fetus for parturition. During
most of the gestation the fetus is lying on it's back with feet pointing up within the
uterus. In last month of gestation, the fetus will rotate into birth position in
the ewe, mare and cow. This normal birth position for lambs, foals and calves is
with the fetus resting on it's abdomen with the
forefeet and nose at the cervix. Fetuses that do not assume this position prior to
parturition are subject to dystocia or difficulty in birthing. In contrast to
the ewe, mare and cow, the sow can usually deliver piglets that are presented at
the cervix backwards as well as those presented in the normal forward position. The
normal forward position of pigs is also somewhat different because the front feet are
normally back against the body, rather than pointing at the cervix. Mammary gland changes are induced by hormonal changes in the
dam. The glands begin to fill with milk and can leak milk from the teats as the dam
nears parturition.
Physiologic changes that take
place in the last days of gestation are:
- Expansion of the pelvis - This takes place as
a result of secretion of the hormones Relaxin and Estrogen and result
in enlargement of the birth canal in preparation for
expulsion of the fetus. The pubic symphysis actually demineralizes, allowing more
expansion of the birth canal as necessary during parturition.
- Sinking around tailhead - The soft
tissues around the tailhead appear sunken and the tailhead is more prominent in the last
day or so prior to parturition. This is due to relaxation of the pelvic ligaments
under the influence of the secreted hormones..
The onset of parturition is thought to be triggered by release of cortisol by the fetus
into the maternal circulation. This results in increased production and release of
estrogen by the placenta. Estrogen causes the muscular wall of the uterus
(myometrium) to begin contracting and preparing to expel the fetus. The uterus
releases prostaglandins (PGF-2a), which, in turn, causes regression of the corpus luteum
and a drop in progesterone levels. Since progesterone inhibits contraction of the
uterine muscles, the drop in progesterone further stimulates uterine muscular
contractions.
As parturitions approaches, a number of additional physical and physiological changes may be observed:
- Vulva softens and becomes swollen
- Cervix becomes dilated.
- Mucus stringing from the vulva.
This is indicative of cervical dilation and expulsion of the mucus plug which sealed off
the uterus to protect it from invasion of microorganisms throughout pregnancy.
- Change in body temperature of
dam. The sow's body temperature rises about 1° C 12-15 hours prior to parturition;
in other animal species, the body temperature drops.
- Rupture of the amniotic sac. This
results in expulsion of amniotic fluid. Laymen will refer to this as the
"Water".
- Dripping milk from the teats.
In addition to the physiological signs of impending parturition, a number of behavioral
signs can be observed, including:
- Isolation from the rest of the flock or
herd.
- Nesting behavior.
- Off feed - most animals will stop eating the day of parturition.
Horses are the exception to this and many will continue to nibble food, even during
parturition.
- Distress, discomfort - this can be
evidenced by restlessness, circling, pawing, biting or kicking at the flank, crying, bawling and groaning.
- Sweating - horses in particular may
sweat across the shoulders and flanks.
Stages of Parturition
Just as there are 3 phases of pregnancy, there are also 3 stages of parturition.
It is important to recognise each stage and monitor the dam to make sure she is
progressing from one stage to the next in a timely fashion. If parturition is not
progressing in a timely fashion, it may be necessary to assist the dam in the
birthing process. In extreme cases, it may be necessary to call on the assistance of
a veterinarian.
The First Stage of Parturition is the
Preparatory Stage. During this stage, a number of important things
happen, including:
- Positioning of the fetus for birth - The normal
position of a fetus is with the front feet pointing out the cervex, right-side up with the
chin resting on forelegs. With cattle, sheep and horses, any other position is
considered an abnormal position and may result in dystocia.
- Dilation of cervix
- Exposure of fetal membranes through the vulva with
possible rupture
In the cow, this stage can last for up to 6 hours. During this time, it is
inadvisable to attempt to assist the dam with delivery. If, however, the dam does
not progress to the second stage of parturition within 6 hours, it is likely that there
are problems with positioning of the fetus that will require assistance. In a full
breech position, where the rump is presented to the cervix and the hind feet are tucked
under the calf's belly, the cervix will not dilate properly due to lack of stimulation by
the nose and front feet of the fetus.
The Second Stage of Parturition is the
Expulsion Stage. During this stage, the following takes place:
- Uterine contractions intensify, leading to
- Abdominal pressing by the dam, followed by
- Expulsion of the fetus
In the cow, this stage of parturition can take up to 4 hours; in the mare, the foal
must be delivered within 15 minutes of the rupture of the amniotic sac, or the foal is
likely to sufficate. The ewe usually delivers each lamb at about 15 minute
intervals. The sow normally delivers piglets at approximately 5-6 minute
intervals. One should assist the dam only after the cervix is fully dilated or you
may damage the cervix and uterus.
The Third Stage of Parturition
is the "Cleaning" Stage. During this stage, the placental membranes
(afterbirth) are expelled. This happens after each birth in cattle, sheep and
horses, however the sow may deliver all the piglets from one uterine horn, expell the
placental membranes from that horn and then deliver the pigs from other horn, or she may
deliver all of the piglets before she "cleans". It is very important to
make sure that the animal finishes the third stage of parturition, because any remnants of
placental membranes left in the uterus will serve as a nidus for infection and could lead
to the death of the dam. In the horse, the placental membranes should be expelled
within 15 minutes of expulsion of the fetus. Swine can take up to 1 hour to expell
the placental membranes, and cattle may take as much as 12 hours to deliver the placental
membranes. After the appropriate length of time, if the membranes are not expelled,
the animal has a retained placenta.
Troubleshooting Parturition Problems
A number of problems
are associated with parturition and it is important to be able to identify the animal that
is experiencing these problems and to assist them or the dam and/or fetus could die.
- Dystocia is
a difficult parturition or difficulty in birthing. It can be caused by several
factors, including:
- Abnormal position of
the fetus. Fetuses that are presented backwards, with one or more front legs back,
or with the head back can cause dystocia and will have to be repositioned or pulled from
the uterus to accomplish delivery. Assistance is similar for delivering calves and lambs
that are presented in an abnormal position. Sows may also need to be assisted in delivery of piglets.
- Oversized fetus -
A fetus that is larger than normal may have difficulty in passing through the birth
canal. In this instance, assistance may also be needed. Breeding of first-calf
heifers to bulls that are known to sire small calves is often practiced to minimise this
problem in heifers which may not be fully mature themselves before delivery of their first
calf.
- Uterine inertia or the lack of ability of the
uterus to contract sufficiently to expel the fetus is a second cause of dystocia.
This may be due to prolonged first stage of parturition or malnutrition of the dam.
- Retained placenta is a second common problem associated with parturition.
- Injections of oxytocin, a hormone that stimulates the
uterus to contract, may aid in expulsion of the placenta.
- Cutting off the exposed remnant of membranes and
infusing the uterus with antibiotics can aid in controlling the uterine infection
(metritis) that accompanies retained placenta.
- Culling animals with a history of retained placenta
may be necessary because severe uterine infections can lead to reduced fertility.
- Nutritional imbalances such as a Selenium deficiency may contribute to retained
placenta.
- Prolapsed uterus is a third, less
common problem associated with parturition. Important management practices dealing
with this problem include:
- Clean the uterus and replace it through the vulva and
vagina, being careful that it is positioned properly.
- Following replacement, administer oxytocin to
stimulate uterine contraction and shrinkage. Suckling also stimulates the release of
oxytocin in the dam, so encouraging nursing of the offspring will also aid in shrinking
down the uterus.
- Encouraging the animal to stand shortly after delivery of the fetus and placenta will
minimize the possibility of prolapsed uterus and getting the animal up after replacing a
prolapsed uterus will aid in repositioning it within the abdominal cavity.
- There is a high likelihood of recurrence within the
first 24 hours of parturition. It this happens it may be necessary to have a
veterinarian perform surgery (Caslick procedure - suturing the vulva shut) to prevent
recurrance.
Immediate Postpartum Care
As a manager, your work doesn't end with the end of
parturition. A number of important steps need to be accomplished to assure the
survival of healthy offspring.
- Observe the offspring and make sure that placental
membranes do not obstruct it's nose, that it is breathing, and able to stand and suckle.
- Watch dam and her offspring to make sure that proper
bonding takes place and she accepts and cares for her offspring. Watch for problems such
as diarrhea, difficulty standing, suckling, etc. The newborn should stand and suckle
shortly after birth.
- If it is bitterly cold, help the dam dry off the
newborn. Piglets will need
supplemental heat provided to keep them from piling on the dam and being crushed when
she moves, or from piling on each other.
- Importance of colostrum - make
sure that the offspring ingests 7-10% of it's body weight in colostrum within the first
12-24 hours of birth. Consider tube feeding, if necessary, to accomplish this.
Ingestion of colostrum is especially important for livestock species, because there is no
transfer of protective antibodies from the dam to the offspring without this. There are many microorganisms within the environment that
can cause the newborn animal to become sick without these protective antibodies recieved
from the dam, who will have developed an immunity to them.
- Mammary gland concentrates antibodies from the dam's
blood
- Intestine of the newborn is only capable of absorbing
these antibodies for 12-24 hrs after birth
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