CHAPTER 42 Parturition and Dystocia
Dystocia (difficult birth) occurs when the first or second stage of labor is prolonged and assistance is required for delivery. No clear boundaries exist between dystocia and eutocia (normal birth), but guidelines based on progress and duration of the delivery may aid the veterinarian and the producer in deciding when to interfere with the birth process. In the last century, a lot of improvement occurred in the techniques used to deliver and resuscitate calves. Only in the last three decades, however, has research been effectively directed toward the causes and management of dystocia. This may be associated with the more widespread implementation of herd health programs and the use of computers to facilitate data management. The incidence of dystocia varies but generally is more common among first-calf heifers, because they have not yet reached their mature size, and then decreases with age.1 Death due to dystocia or as a result of injuries sustained during delivery is the most common cause of calf loss during the first 96 hours post partum, with most losses occurring during the first 24 hours after delivery.2,3 The subsequent pregnancy rate among dams that suffer dystocia also is reduced.4–6 Although it is not possible to eliminate dystocia, improvements in management of heifers during their development and observation of cows and heifers during the calving season are critical for reducing calf losses.
This chapter begins with a description of the process of normal parturition (eutocia). The diagnosis and treatment of dystocia are described next. Finally, owing to the importance of dystocia control and prevention, management techniques used to reduce the incidence of dystocia are discussed, with the main focus on specific control measures.
During the last weeks of gestation, the dam prepares for delivery of the fetus and the initiation of lactation. Enlargement of the udder may begin in heifers at 5 to 6 months of gestation but may not be obvious in pluriparous cows until the last weeks of pregnancy. The gland may become tightly swollen, and in severe cases, edema may be so extensive in dairy cows as to require induction of parturition or initiation of milking several days before calving. Initial secretions that can be expressed from the mammary gland are viscid and pale yellow to amber in color. As parturition approaches, colostrum is secreted and is white to yellow, turbid, and opaque. The pelvic ligaments relax under the influence of estrogens, relaxin, and the general hormonal milieu that initiates parturition; the gluteal muscles sink, the tailhead becomes more prominent, and the cranial border of the sacrosciatic ligament becomes less tense. A few hours before calving, the vulva becomes edematous, and the cleft elongates. Unfortunately, none of the signs of approaching parturition are specific enough to permit a precise prediction of the exact time of calving; thus, veterinarians have been admonished “to refrain from making too positive or definite a statement regarding the exact time of parturition, as subsequent events will more often than not prove him wrong.”7 Once initiated, delivery of a calf is a continuous process, but for the convenience of discussion, most authors divide labor into three stages or phases.
The first stage of labor signals the beginning of delivery and is characterized by progressive relaxation and dilation of the cervix.8,9 Increased output of adrenocorticotropic hormone (ACTH) and associated cortisol from the fetal adrenals leads to an increase in the level of the enzyme 17α-hydroxylase in the fetal placenta.10 This in turn reduces placental progesterone production by allowing pregnenolone to be metabolized through to dehydroepiandrosterone. Maternal plasma progesterone concentrations then decrease because pregnenolone is diverted through to estrogen production, and maternal plasma estrogen concentrations subsequently increase. In addition to converting progesterone to estradiol, fetal corticoids also cause the placenta to synthesize prostaglandin F2α (PGF2α). The synthesis of PGF2α helps abolish the progesterone block to myometrial contractility. As both estradiol and prostaglandin become elevated, the myometrium becomes increasingly more motile and begins to display noticeable contractions. Also, PGF2α causes the corpus luteum of pregnancy to regress, facilitating the decline in progesterone.
As the pressure inside the uterus continues to increase, the fetus rotates so that its presentation is with the front feet and head pointing toward the caudal aspect of the dam. This rotation is important to ensure an uninterrupted delivery. If the fetus fails to achieve the correct presentation, position, or posture, because of either disease or lack of space, dystocia may occur.
The external cervical os of cows may be sufficiently relaxed to admit two to four fingers as much as a week before calving, but the cervix of heifers usually remains tightly closed until the day before calving, when it begins to relax. Dilation of the cervix occurs in two phases. During the preliminary phase, the cervix dilates passively by a decrease in cervical tone. Dilation of the internal cervical os begins 2 to 4 hours after the external os reaches a diameter of 6 to 12 cm. The active phase of cervical dilatation begins approximately when the external os has dilated sufficiently to permit the introduction of a hand and is initiated by increased concentrations of estradiol, coupled with the elevation in levels of PGF2α. These hormones induce strong contractions of the myometrium that pull the cervix open and force the fetus and its membranes into the partially dilated cervical canal. Complete cervical effacement occurs when a portion of the fetus enters the cervix and applies mechanical pressure from within the canal.
Pressure on the cervix brought about by increased myometrial contractions and presence of the fetus activates pressure-sensitive neurons located in the cervix that synapse in the spinal cord and eventually synapse with oxytocin-producing neurons in the hypothalamus. Oxytocin released into the systemic circulation acts to facilitate the myometrial contractility initiated by estradiol and PGF2α. As pressure against a cervix continues to increase, so does the oxytocin secretion, and the force of contraction of the myometrial smooth muscle begins to peak. With application of this maximal force, the fetal head and forelegs completely enter the cervical canal, the chorioallantois usually ruptures, and the first stage of parturition is complete. At the end of the first stage of labor, the cervix and the vagina are a continuous canal.
It occasionally may be necessary to differentiate between dystocia caused by incomplete cervical dilatation and prolonged first-stage labor. A differential feature of the conditions is that progressive enlargement of the cervical canal can be discerned between two consecutive examinations in cases of prolonged first-stage labor, whereas the status of the cervix remains unchanged in cases of incomplete dilatation.
Clinical signs associated with the first stage of labor most often are observed in primiparous animals; the signs may be minimal or pass unnoticed in older dams. The signs of the first stage of labor generally are those associated with abdominal discomfort and include a variable degree of anorexia, restlessness, shifts of weight from one leg to another, and presence of an arched back with elevated tail. If given the opportunity, most dams will seek solitude away from the remainder of the herd. Some dams may demonstrate mild and intermittent abdominal straining during the late portions of the first stage; thus, the demarcation between the first and the second stage is not as clear in cows as it is in mares. Rupture of the chorioallantois and release of the allantoic fluid (“breaking water”) may be a more accurate attribute by which to mark the end of the first stage of labor. The average duration of the first stage of labor is approximately 6 hours, but considerable variation among animals is observed, and the stage may last up to 24 hours in heifers.11
The fetus is delivered during the second stage of labor, which is characterized by the application of strong abdominal pressure by the dam. Myometrial contractions stimulated by oxytocin force the fetus into and stretch the cervical canal. In particular, the conical shape of the head as the nose enters the cervical canal is important because it progressively dilates the cervix with mechanical pressure. Stretching stimulates the release of more oxytocin from the maternal pituitary gland, which causes further uterine contractions. Oxytocin is thought also to stimulate release of prostaglandins from the endometrium, which further stimulates myometrial contractions.12 This positive feed-forward system makes it difficult to stop labor once it has begun. Forms of dystocia that delay or prevent entry of the head or limbs of the fetus into the cervix, to stimulate the pressure receptors, result in little if any abdominal straining by the cow. A typical example is cranial presentation with full flexion of the hips (true breech presentation).
The intact amnion should appear at the vulva as a fluid-filled sac shortly after rupture of the chorioallantois. After the amnion appears, the dam alternates frequently between standing and recumbency. The amnion usually ruptures while the dam is recumbent, and rupture is followed by regular bouts of abdominal straining. Early in the second stage of labor, each bout of abdominal straining consists of 5 to 7 abdominal contractions, which increases to 8 to 10 contractions as the process advances. The cow usually rests in sternal recumbency and may eat between bouts of abdominal straining. As delivery continues, the length of rest periods decreases and the force of abdominal contractions increases. As the contractions become more forceful, the dam rolls to lateral recumbency and lifts the head, hindquarters, and uppermost limbs and may vocalize with each effort. Maximal force is required to deliver the fetal head through the vulva, and in most instances of eutocia the remainder of the fetal body follows with little or no additional effort. In the case of large calves, additional abdominal pressure may be required to deliver the fetal shoulders or hindquarters. Most cows deliver their calves while in lateral recumbency, but a few may complete delivery while standing. Delivery while standing is more common in pluriparous dams than in heifers and may be the result of unintentional disturbance of the cow caused by handlers.
The average length of the second stage of labor in pluriparous cows is 2 to 4 hours, but this stage is longer in heifers because more effort is required to dilate the tissues of the birth canal. A healthy bovine fetus can survive for up to 8 hours after the beginning of the second stage of labor provided that the umbilicus remains intact; survival is longer when uterine contractions are weak or infrequent. Exhaustion and secondary uterine inertia result in cessation of uterine and abdominal contractions after 8 to 12 hours of labor.
The third stage of labor is characterized by detachment and expulsion of the cotyledonary placenta. Expulsion of the fetal membranes requires that the chorionic villi become dislodged from the crypts of the maternal side of the placenta. This release of the chorionic villi is believed to be brought about by powerful vasoconstriction of arteries in the villi associated with continued myometrial contractions. Uterine contractions continue after delivery of the fetus and sometimes are fortified by occasional bouts of abdominal straining. Myometrial contractions gradually subside in frequency and amplitude and are not detectable by 2 to 4 days after calving. The time required for expulsion of the placenta averages 8 hours but can range from a few minutes up to 12 hours without being considered abnormal. Most dams rise during the third stage of labor and begin to groom their calf, licking first its hindquarters and then the head and neck. Dams usually continue to face and lick their calves after they stand but soon allow the calf to move alongside, seek the udder, and nurse.
Causes of dystocia related to management practices are discussed later in the chapter. From a clinical perspective, the etiology of dystocia is multifaceted and includes defects in the dam or the fetus and management factors, or a combination.13 For purposes of formulating a clinical management plan for an individual animal, it is convenient to divide the causes of dystocia into those of maternal origin and those of fetal origin. It is important to remember, however, that clinical cases may result from multiple underlying disorders and also may require medical treatment to correct concurrent problems, in addition to the more traditional mechanical or surgical treatments.
Primary uterine inertia is characterized by failure of the myometrium to contract normally and bring the fetus into the cervical canal. The condition is encountered occasionally in cows, and causes that have been suggested include overstretching of the uterus by multiple or abnormal fetuses, a defect in the myometrium that renders it unable to contract normally, a defect in the hormonal milieu (see the description relating to ineffective labor and physiologic dystocia under “Management and Prevention of Dystocia” later on), and periparturient hypocalcemia. The dam may exhibit a few weak abdominal contractions but does not progress to the second stage of labor. On examination, the cervix is found to be dilated but the fetus has not yet entered the birth canal. The fetal membranes may be intact if labor has not been prolonged. Calves usually are delivered by gentle traction after correction of any defects in posture or position.
Secondary uterine inertia is a result of exhaustion of the myometrium after prolonged unsuccessful attempts to deliver a fetus. Treatment is directed at removing the impediment and delivering the fetus by a method appropriate for the clinical circumstances. Sequelae of secondary uterine inertia include retained placenta, delayed uterine involution, and uterine prolapse.
Delivery may be inhibited by inadequate size of the maternal pelvis, pelvic deformities or exostoses, incomplete dilatation of the cervix, vaginal cystocele, neoplasms of the vulva and vagina, remnants of the müllerian ducts persisting as bands of tissue from the dorsal to ventral walls of the vagina immediately caudal to the cervix, and uterine torsion. Stenosis of the vulva and vestibule may be the result of immaturity or may be a heritable defect in some breeds.
Broadly, the fetal origins of dystocia in cattle can be divided into those caused by abnormalities of the fetus (defects in fetal disposition and various forms of maldevelopment resulting in fetal monsters) and those caused by excessive fetal size relative to the maternal pelvis (fetopelvic disproportion).
See the later section “Mutation of Abnormal Presentation, Position, and Posture” for definitions of these and related terms. For normal delivery in cattle, the fetus is in cranial longitudinal presentation and in dorsosacral position, with the head, neck, and forelimbs extended. Caudal presentations are considered abnormal in cattle, but unassisted delivery can occur with the fetus presented caudally if the hindlimbs are extended. Spontaneous delivery with other fetal presentations, positions, or postures is unlikely unless the fetus is quite small or the dam’s pelvis is unusually large.
A variety of malformations resulting in specific fetal phenotypes and conjoined twins have been described as sporadic causes of dystocia in cattle. Among the fetal monsters more likely to be encountered in cattle are schistosomia reflexus and perosomus elumbus. Schistosomia reflexus, shown in Figure 42-1, is characterized by extreme ventral curvature of the spine, so that the head is positioned near the sacrum. The abdominal and thoracic walls are not closed, and the viscera are exposed. Limbs of the affected fetus frequently are rigid because of ankylosis of the joints.
The most common cause of dystocia in cattle is fetopelvic disproportion. The situation is most common in heifers where the fetus is of normal size for its breed but the maternal pelvis is of insufficient size (relative oversize) or the fetus may be unusually large and cannot be delivered through a pelvic canal of normal size.
The spectrum of clinical presentations encountered by veterinary obstetricians is immense. The diagnosis of dystocia usually is made by the owner or manager of the animal, who may decide to seek professional assistance early in the course of delivery or not until labor has been unduly prolonged.
The first step in clinical evaluation of bovine dystocia is to obtain as much pertinent history as possible. Although the usefulness and accuracy of the history will vary with the diligence of the manager, the clinician should attempt to obtain at least a minimal amount of information before initiating the examination.
If the clinician is not already familiar with the client’s management style, it can be useful to gain a brief summary of previous dystocia cases and breeder management. Information on the bull used for the mating period also may be useful in determining the etiology of the current problem, in addition to providing insight for future recommendations. To save time, much of this information can be extracted during conversation as the clinical evaluation proceeds.
The breeding date, if known, should be ascertained. If delivery is premature and dystocia is associated with abortion, the clinician can take steps to reduce or eliminate exposure to infectious causes of bovine abortion that are zoonotic. Prolonged gestation is in most cases associated with excessive fetal size and poor viability.
It is important to know how long the animal has been in labor. Cows and heifers should be allowed a reasonable amount of time to spontaneously deliver their calves. It is common for cows to vocalize during straining early in stage two of parturition. This is associated with stretching of the soft tissues of the birth canal.14 Thus, although clinical judgment is necessary, the amount of vocalization during straining may be used as a rough guide to the duration of stage two if the history is not available. If an adequate time for the first or second stage of labor has been exceeded, examination is indicated. Heifers should be allowed a longer time for spontaneous delivery than is required in pluriparous cows. If intervals between observations are excessive (more than 3 hours), the manager will be unable to accurately determine the time of onset of labor, and immediate intervention may be justified. Early obstetric assistance has been shown to improve the subsequent fertility of beef cows.15
The character of the expulsive efforts should be determined–whether they are weak and sporadic or substantial and frequent. In some individual animals, stage two labor may be manifested as only a few weak attempts to deliver the fetus before secondary uterine inertia supervenes. Vigorous and forceful attempts should result in steady progress; if they do not, the dam should be examined.
The clinician should determine if the fetal membranes have ruptured. Rupture of the chorioallantoic membrane and release of the watery allantoic fluid serve to indicate the onset of the second stage of labor. Rupture of the amnion is followed by release of the viscous amniotic fluid. Examination is indicated if delivery is not complete within 2 hours after the amnion appears outside the vulva.
It is important to determine if the patient has been examined, or if any attempts have been made to deliver the calf before attendants sought professional assistance. The ability of managers to determine the cause of dystocia varies, but the results of a proficient examination may be useful to the clinician. Information regarding futile attempts at delivery by attendants may be difficult to elicit, but damage to the birth canal or fetus caused by well-intentioned but inappropriate efforts should be discovered before intervention lest the veterinarian be held responsible.
Accessible facilities and demeanor of the patient often dictate the restraint used for examination and relief of dystocia. Facilities and conditions often are less than optimal. Ideally, however, confinement of the parturient dam should be in a dry, well-bedded enclosure of generous size and with sufficient illumination. Difficult vaginal deliveries often are assisted if the dam can be placed in lateral recumbency; therefore, room to cast and restrain a recumbent animal is ideal. Access to a clean water supply also is desirable. A squeeze chute may be suitable for the initial examination, but the inclination of most cows to become recumbent during traction makes this choice undesirable in all but the simplest of deliveries. Although extraction of the fetus is better performed with the dam in lateral recumbency, the initial examination is more readily performed with the animal standing, because pressure within the abdomen is reduced in this posture. Thus, the patient is most conveniently restrained with a halter, but a stanchion or head bail may be used if caution is exercised to prevent asphyxiation or excessive pressure on the carotid arteries should the animal become recumbent during the examination. During delivery, sufficient space should be available behind the patient to allow manipulation of a fetal extractor or fetatome. A position of lateral recumbency can be achieved with a combination of ropes and sedation. Figure 42-2 shows ropes set on a heifer in preparation for casting in lateral recumbency once diagnostic traction has confirmed that vaginal delivery is possible.
Fig. 42-2 Rope placement for casting a heifer before vaginal delivery of the fetus. The side of the chute has been opened in preparation for releasing the head bail and allowing the heifer to exit through the side of the chute. Note that the halter rope is pulled back through the head bail and tied down low to the ground. Sedation may be administered immediately before opening the chute if necessary.
Administration of an epidural anesthetic is not routinely performed if vaginal delivery is to be used, because in most instances the expulsive efforts of the dam are beneficial in assisting delivery. Desensitization of the birth canal and the perineal area usually is reserved for cases that require moderate to extensive manipulation of the fetus before extraction, fetotomy, or surgical delivery is attempted.
The clinician should note the general condition of the patient and identify abnormalities that may potentially influence the selection of a method to relieve the dystocia or have an impact on the prognosis. For example, overconditioned feedlot heifers have excessive deposits of fat in the pelvic canal, which reduces its caliber and increases the difficulty of delivery. Recumbent animals should be examined for the possibility of exhaustion, calving paralysis, or hypocalcemia. Pallor of the mucous membranes may suggest internal hemorrhage due to rupture of one of the large blood vessels that supply the uterus. The character of any discharge from the birth canal or any exposed portion of the fetus or membranes should be noted. Fetid or sanguineous discharges are more typical of protracted cases. Yellow-brown discoloration of the fetus or fluids by meconium is an indication of fetal hypoxia, and immediate intervention is indicated.
Examination of the reproductive organs by palpation per rectum is indicated in only a few cases of dystocia. The most common indication for rectal palpation is to confirm uterine torsion when stenosis of the cranial vagina is detected during a vaginal examination. Pelvic deformities and exostoses may be more readily detected by palpation per rectum than by vaginal examination. Other indications for palpation per rectum include elicitation of spontaneous movements of the fetus when it is not possible by vaginal examination, confirmation of uterine rupture, and recognition of hemorrhage into the broad ligaments. Although unusual in cattle, firm feces should be removed from the rectum before the application of extractive force.
Vaginal examination in dystocia almost always implies manual entry into the birth canal. In rare cases, however, speculum examination may be more suitable than manual techniques. Such cases include those in which straining is minimal and conception dates are only approximate.
Two essential requirements for effective obstetric intervention with minimal post-treatment complications are cleanliness and lubrication. Before invasion of the birth canal, the vulva and perineal area and any protruding fetal parts are washed with surgical soap and water. The hands and arms of the operator also are cleansed. Some clinicians prefer to wear shoulder-length plastic sleeves, whereas others find that wearing these sleeves reduces sensitivity and interferes with a thorough examination. Clinicians should be familiar with zoonotic diseases in their geographic area and take appropriate precautions. The hands and arms should be coated with a generous amount of a nonirritating obstetric lubricant before entry into the vaginal canal. It often is beneficial to pump 3 to 5 L of lubricant into the birth canal, in addition to applying lubrication to the operator’s arms. Note that despite the long-standing doctrine of using warm soapy water during obstetric intervention, soaps are not the ideal product for the job. Although they may provide some short-term lubrication, they quickly increase the friction encountered owing to their propensity to cut fats and oils from the contact surfaces. In protracted cases with autolytic changes in the fetus, some clinicians elect to apply generous amounts of lanolin or barrier cream to the arms in order to reduce skin irritation and folliculitis, which may result from prolonged exposure to fetid tissues and fluids.
The birth canal and fetus are first examined for lesions or hemorrhage that may have been induced by previous attempts at delivery, and the caretaker is informed of their presence. The operator then determines as accurately as possible the presentation, position, and posture of the fetus and the presence, if any, of congenital abnormalities. In some cases, it is difficult to determine if the forelimbs or hindlimbs of the fetus are present in the birth canal; fetal elbow and fetal hock may have similar characteristics on palpation, which may confuse even the experienced operator. The limbs can be differentiated by starting at the hoof and counting the joints from distal to proximal up the limb. The forelimb has a carpal joint between the fetlock joint and the elbow, whereas on the hindlimb, the hock joint is palpable immediately proximal to the fetlock joint. The ears, eyes, and mandible can be used to identify the head, whereas the presence of the tail indicates a caudal presentation.
If the fetus is in dorsosacral position and the soles of the fetal hooves are directed ventrally, the limbs presented to the birth canal are the forelimbs, whereas if the soles are directed dorsally, the hindlimbs are presented first. The disposition of fetuses in transverse presentations sometimes is difficult to ascertain, and a careful examination is required. Fortunately, transverse presentation is rare in cattle, being commonly associated with fetal deformities or fetal monsters such as schistosoma reflexus.
Although cattle generally are considered to be uniparous, twins and greater multiples are not rare; thus, the number of fetuses must be determined and their appendages identified. The location of the internal septum between the two uterine horns is identified so it will not be inadvertently damaged by the wire saw should a fetotomy be selected as the method by which to relieve dystocia.
After determining the disposition of the fetus, the clinician then must determine if it is alive or dead before selecting the appropriate method to complete delivery.24 In cranial presentation, the interdigital claw reflex can be elicited by pinching the web of tissue between the claws. A vigorous fetus responds by withdrawing the foot. A false positive result may occur if the operator mistakes movement caused by the maternal abdominal press for that of the fetus. False negative results can occur in live calves if the head and limbs are wedged in the birth canal. The swallowing reflex is elicited by applying pressure at the base of the tongue, to which a normal calf responds by swallowing or sucking. Slow or exaggerated reactions may be associated with hypoxia or may be agonal. Slight pressure on the eyeball elicits movement of the eyeball or eyelid. The eye reflex is preserved even in severely acidotic calves. The reflexes disappear in a peripheral to central progression as the condition of the fetus deteriorates. That is, the reflexes requiring the longest nerve pathways disappear before those with shorter nerve pathways as acidosis increases. Thus, the interdigital claw reflex disappears first, and the eye reflex is preserved longest. This differential loss of peripheral compared with central reflexes may aid assessment of the physiologic status of the calf.
In caudal presentation, the interdigital claw reflex of the hindlimb is similar to that in the forelimbs; however, it becomes negative earlier during the course of delivery than does the reflex in the forelimbs. Thus, the interdigital claw reflex may be negative in a viable calf, and elicitation of this reflex is a good prognostic sign. The anal reflex sometimes is used to assess the status of a fetus in caudal presentation. This reflex is elicited by pushing the examiner’s finger against or into the anus. Evaluation of the response is subjective, however, and the reflex can be absent in a viable fetus.
If the fetal reflexes are ambiguous or absent, the obstetrician should examine the fetal heartbeat or umbilical cord pulse. The heartbeat can be palpated by passing the hand between the fetal forelimbs along the ventral aspect of the neck to the sternum. The fetal heartbeat is then palpable with the examiner’s fingers placed on the left side of the fetal thorax. Palpation of the heartbeat in fetuses presented caudally is difficult. The normal intrauterine heart rate in calf fetuses of 70 to 120 beats per minute increases to 90 to 120 beats per minute during delivery. The heart rate may fall to 40 to 60 beats per minute during uterine contractions. Hypoxia of the dam caused by excitement or exertion can lead to a more severe drop in fetal heart rate. Prolonged or excessive extractive force can cause the fetal heart rate to drop to near zero. As a calf becomes acidotic as a result of delayed delivery, the heart rate first increases to 140 beats per minute and then falls and becomes irregular as its condition deteriorates.
The umbilical cord of fetuses in cranial presentation is located by palpating it between the last rib and the abdomen. In caudal presentation, the umbilical cord is easily accessible. Pulsation of the umbilical vessels can be felt by applying slight pressure to the cord. The cord may be wrapped around the fetal abdomen or limb or may enter the birth canal alongside the fetus. Although not commonly required, the location of the cord can be ascertained and the cord repositioned if necessary. Pressure on the cord should be avoided during mutation of malpostures and during extraction.
Severe congestion of the head, tongue, and forelegs is the result of prolonged impaction of the fetus in the birth canal. The condition may occur in vigorous or moribund calves and does not suggest a prognosis. If delivered alive, affected calves have difficulty nursing and may require assistance plus the administration of anti-inflammatory agents.
After the status of the fetus has been determined, the operator then must estimate the size of the fetus relative to the size of the maternal pelvic inlet and birth canal. Delivery by traction results in fetal respiratory acidosis, and the operator must determine if the risks of harming the dam and the fetus during extraction are justified.
For inexperienced obstetricians, effective guidelines have been formulated to assist in the decision-making process for determining if vaginal delivery is possible.14 The basis for these guidelines sometimes is referred to as “diagnostic traction.” When the fetus is in cranial presentation, dorsosacral position, and normal posture, if one person can pull the fetlocks 10 to 15 cm beyond the vulva (approximately one hand’s breadth), the points of the shoulders will pass the maternal iliac shafts and the calf can be delivered vaginally if correct delivery techniques are used. When the fetus is in caudal presentation, dorsosacral position, and normal posture, if one person pulling on each leg can make the hocks appear at the vulva, the greater trochanters will pass the iliac shafts and the calf can be delivered vaginally. As experience is gained, other factors can be included in the decision-making process. For example, the chance for successful delivery by traction is increased in the following circumstances14:
The vaginal examination is concluded by assessing the degree of dilatation of the vagina, vestibulovaginal sphincter, and vulva. Most ruptures of the vagina, vulva, and perineum occur during obstetric intervention and should be prevented by manual dilatation of the birth canal before application of traction. Manual dilatation of the caudal reproductive tract is an extremely important part of delivery technique, with many clinicians suggesting that the need for episiotomy can be dramatically reduced if time is taken to ensure that effective dilatation is achieved before application of traction. In addition, the stress and resultant acidosis in the calf are reduced, because resistance to delivery of the head and thorax is less. After application of an obstetric lubricant, the birth canal can be stretched by clasping the hands together and inserting both arms. Outward pressure with the forearms is placed in a diagonal direction with one forearm at the 2 o’clock position and the other forearm at the 8 o’clock position. Continual pressure is applied in the form of a wedge for as long as the operator can manage; then the arms are moved to the other diagonal of 4 o’clock and 11 o’clock, and the procedure is repeated. Tenacity is essential, because 10 to 20 minutes may be required to dilate the birth canal sufficiently to prevent soft tissue injury.
On completion of the examination and assessment of the condition of the fetus, the dam, and the birth canal, the clinician must then formulate a plan for resolution of the dystocia. The available options in cattle are mutation of abnormal presentation, position, or posture; forced extraction; fetotomy; pelvic symphysiotomy; and cesarean section.16 Euthanasia may be indicated in situations in which the value of the animal is limited and the prognosis poor. When formulating a plan to deliver the fetus, the clinician must consider the value of the dam and the potential value of her offspring, the cost of the procedure and aftercare, and the prognosis for the life of the dam and the fetus and for the dam’s future reproductive performance. Often, the facilities and assistance available, as well as the personal preferences of the animal’s owner and the clinician, will influence the decision. Figure 42-3 is a flow diagram of the decision-making process that can be used by the clinician in clinical management of dystocia.
Presentation is the relation of the spinal axis of the fetus to that of the dam. Presentation can be either longitudinal or transverse. The fetus’ orientation is either cranial or caudal in the longitudinal presentation and dorsal or ventral in the transverse presentation. Cranial longitudinal is considered the normal presentation. Note the general trend away from the traditional use of the human descriptors of anterior and posterior in veterinary science.
Position is the relation of the dorsum of the fetus to the quadrants of the maternal pelvis. These quadrants are the sacrum, right ilium, pubis, and left ilium. Dorsosacral is considered the normal position.
Posture is the relation of the fetal extremities (head, neck, or limbs) to its own body. Extremities may be flexed, extended, or retained (usually referring to the head). Retention can be to the right, to the left, or above or below the fetus.
Mutation is defined as the process by which a fetus is restored to normal presentation, position, and posture by repulsion, rotation, version, or extension of extremities. Abnormalities of fetal posture generally are easier to correct when the dam is standing. In specific circumstances, however, placement of the dam in lateral recumbency can be advantageous, particularly if facilities such as a hydraulic tilt table or even a sloped loading ramp are accessible. For example, with retention of the fetal head, if the cow can be placed in lateral recumbency with the fetal head uppermost and the forequarters of the cow elevated slightly, mutation of the head to a normal posture can be facilitated. If mutation cannot be completed in 15 to 30 minutes, an alternate method for delivery should be selected.
Repulsion of the fetus out of the maternal pelvis into the uterine cavity where more space is available for correction is the first step in mutation. The fetus and birth canal must be well lubricated, and 3 to 5 L of a water-based lubricant can be gently introduced around the fetus through a stomach tube by means of a pump. It may be necessary to abolish abdominal straining with an epidural anesthetic, but the expulsive efforts of the dam will not subsequently be available for delivery of the fetus. In countries where it is registered for use, clenbuterol may be administered to assist in relaxation of the uterine musculature.
Care should be exercised in repelling a fetus, because uterine rupture may result from excessive pressure. Various instruments have been used for repulsion of a fetus, the most commonly used device being the Kuhn’s crutch. In general, however, use of the operator’s hands and arms is recommended to reduce the risk of uterine rupture below that associated with introduction of metal instruments into the uterus. In neglected cases, the uterus may be tightly contracted around the fetus, and repulsion should not be attempted.
Rotation is defined as turning the fetus on its longitudinal axis to bring it from dorsoilial or dorsopubic position to dorsosacral position. Partial rotation also is an essential component of the routine vaginal delivery technique to ensure that the fetal hips enter the maternal pelvis on a diagonal.
In many cases, rotation can be accomplished by the hand and arm of the operator. By grasping the humerus of the ventral limb near the shoulder joint, the operator lifts the fetus upward and medially. If an assistant is available, traction on the dorsal fetal limb in a downward and medial direction can be applied to aid in rotating the fetus. Alternatively, the fetal limbs can be crossed and rotational force applied to bring the fetus to dorsosacral position. In difficult cases, use of a detorsion rod may be necessary, but excessive force that may result in injury to the dam and the fetus should be avoided.
Version is defined as turning the fetus on its transverse axis into cranial or caudal presentation. Transverse presentation fortunately is rare in cattle but must be converted to longitudinal presentation before delivery is attempted. Extractive force is applied to the portion of the fetus closest to the maternal pelvis while the opposite pole of the fetus is repelled. Version usually is limited to 90 degrees, and attempts to convert caudal presentation to cranial presentation are not likely to be successful and will commonly result in uterine tears.
Mutation of malposture of the fetal extremities usually requires that the fetus be repelled out of the maternal pelvis before attempts at correction. In general, correction of flexion of an extremity is accomplished by repelling the proximal end, rotating the middle portion laterally, and applying traction to the distal end. Repelling and rotating forces can be applied with the operator’s hand. Traction can be applied by the operator if sufficient space is available in the birth canal to permit the introduction of both arms, or by an assistant using an obstetric chain or snare.
In cattle, the head most commonly is deviated to the left side of the fetus and lies against the thoracic wall. The malposture is corrected by grasping the orbital grooves with the thumb and middle finger (forceps grip) and drawing the head into the maternal pelvis. A rope snare placed behind the incisor teeth may be useful in difficult cases. Traction to redirect the head can be applied with the snare by the operator or by an assistant while with the other hand the operator guides the head and protects the uterine wall from the incisor teeth by covering the fetal mouth.
The head may be deviated ventrally between the forelimbs, with the mandible resting against the sternum. A hasty examination may fail to reveal the presence of the head, and the malposture may be mistaken for a case of caudal presentation. In some instances, the malposture can be corrected by repelling the fetal forehead with the thumbs while simultaneously lifting the jaw with the fingers. Correction in more severe cases requires that one or both forelimbs be repelled and flexed at the carpus, elbow, and shoulder joints. Space is then available to convert the ventral displacement of the head to lateral displacement, which is then corrected by drawing the head into the pelvis. The induced malposture of the forelimb is subsequently corrected after the head is in its proper position. Should attempts to reposition the head by these methods not be successful, the dam can be sedated, cast, and rolled to dorsal recumbency. The fetus then falls toward the maternal spine and away from the narrow ventral portion of the pelvis, allowing the head to be more easily guided into the pelvic canal.
Unilateral or bilateral carpal flexion can be responsible for dystocia in cattle. If the flexed carpus along with the fetal head is within the maternal pelvis, the situation is described as engaged carpal flexion, whereas if the flexed carpus is cranial to the maternal pelvis it is described as disengaged carpal flexion. Correction requires that the fetus and the flexed limb be repelled cranially out of the pelvis to increase the space available for correction. The operator introduces the hand corresponding to the side of the displacement into the birth canal and grasps the metacarpus immediately proximal to the fetlock. Then the limb is lifted dorsally and the shoulder and elbow joints are flexed. When the fetlock is above the pubis, the hoof is cupped in the hand and pulled into the pelvis. If needed, traction can be applied with a snare placed proximal to the fetlock joint. While lifting and repelling the carpus with one hand, the operator applies gentle traction to draw the hoof into the pelvis with the other.
The shoulder joints also may be unilaterally or bilaterally flexed and the forelimb positioned alongside or under the fetal abdomen. Correction is accomplished by grasping the radius and pulling it toward the maternal pelvis. Shoulder flexion is thus converted to carpal flexion, which is then corrected by the methods previously described. If a traction snare can be placed distal to the carpal joint, it can be used to apply extractive force with one hand while the other repels the shoulder joint.
Shoulder-elbow flexion or elbow lock posture is most common in heifers and results in impaction of the elbow joints on the pelvic brim. The condition is recognized when the muzzle of the fetus lies directly above the hooves, rather than in its normal position approximately at the middle of the metacarpus. The malposture is corrected by first repelling the fetal body into the birth canal and then applying traction to the affected limbs, one at a time, until the elbow and shoulder joints are fully extended.
Foot-nape posture is not common in cattle but arises when one or both of the forelimbs is displaced upward to lie on top of the head and neck. The defective posture is corrected by grasping the fetlock of the affected limb and forcing it downward and laterally while simultaneously lifting and repelling the head with the other hand until the forelimbs are in their normal position. In protracted cases, continued attempts to deliver the fetus may force the hoof through the dorsal wall of the vestibule, resulting in the formation of a fistula or perineal laceration.
Displacement of the hindlimbs is rarely a problem unless the fetus is in caudal presentation. The incidence of caudal presentation in cattle can vary depending on management conditions and genetics, and such displacements frequently are complicated by dystocia. One or both hindlimbs may be retained and flexed at the hock or at the hip.
To correct hock flexion posture, the limb is grasped at the metatarsus and repelled cranially and laterally until sufficient space is available to draw the hoof in a caudal and medial direction into the pelvic canal. The operator should cover the hoof with one hand to protect the uterine wall as it is rotated medially. In some cases, application of a snare distal to the fetlock joint can facilitate correction. The cord is placed between the digits of the affected hoof, and traction is applied. The operator then applies opposing forces by repelling the hock while simultaneously applying traction to the snare. This action results in flexion of the fetlock and pastern joints while the hoof is drawn toward the pelvic brim.
Bilateral hip flexion (colloquially referred to as “true breech” presentation) prevents entry of the fetus into the cervix; thus, the stimulus for the abdominal press is lacking, and signs of the second stage of labor may be minimal or absent. Hip flexion is corrected by grasping the lateral aspect of the tibia as closely as possible relative to the hock. The hock and stifle joints are flexed by drawing the hock toward the maternal pelvis. After the hock and stifle joints are fully flexed, the malposture becomes hock flexion, which subsequently is corrected as previously described.
Ventrovertical, or dog-sitting, position causes dystocia in fetuses presented cranially because of flexion of the hindlimbs at the hips. The hooves may be impacted against the maternal pelvis or lie in the vagina alongside the forelimbs. The cranial portion of the fetus is delivered normally, but the impediment is discovered when delivery cannot be completed. The condition is diagnosed by careful examination, which may be difficult if the cranial portions of the fetus occupy the pelvic canal. An attempt may be made to correct the malposture by repelling the hindlimbs as deeply as possible into the uterus. Correction is likely to be successful only when the fetus is small. Delivery by cesarean section or fetotomy may be preferable in many cases.