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 dog whelps and gives birth to puppies
    A cow calves and give birth to a calf
    A sow farrows and gives birth to piglets
    A ewe lambs and give birth to lambs
    A horse foals and give birth to a foal

    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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