CHAPTER 91 Lambing Management and Neonatal Care
Approximately 40 days after the ram is removed from the flock, scanning for pregnancy using real-time ultrasound examination is recommended to identify those animals that are not pregnant. To improve nutritional management of late-gestation ewes, fetal number also should be determined and ewes classified by body condition score.
Gestation length varies considerably with breed of sheep. It also varies within breed with number of fetuses being carried. Triplet-bearing ewes usually lamb before single-bearing ewes bred on the same day. On average, sheep gestate for 145 days. Normal lambings have been reported as early as day 137, but generally sheep do not lamb earlier than day 142.
At 1 week before the first expected lambing date (day 138 after the ram is introduced to the breeding flock), ewes should be observed every 4 to 6 hours. Diseases to observe for include signs of pregnancy toxemia, which include refusal to eat grain, opisthotonos, teeth grinding, fine muscle tremors, and coma; signs of hypocalcemia, which include stilted gait, excessive salivation, and recumbency with hind legs extended behind; vaginal prolapse; abortion; mastitis; and rupture of the prepubic tendon. If any of these conditions occurs, prompt treatment should be instituted.
Signs of the first stage of labor include udder enlargement and engorgement with colostrum, relaxation of the pelvic ligaments, and vulvar swelling. The ewe will separate from the flock and begin nesting. If on pasture, she will seek an isolated spot with slight elevation or close to a fence line. Ewes may seek shelter, if it is provided, in order to protect their newborn lambs from inclement weather. Within a paddock, ewes may choose the same location in which to give birth, presumably attracted by the scent of birth fluids. In a pen, ewes may seek a corner or an open claiming pen. She will circle, paw at the straw, and bleat in a low voice. She will stop to smell any uterine or vaginal discharges. As the uterine contractions become stronger and the fetus moves up into the pelvis, she may lie down repeatedly and strain with the head raised.
The second stage of labor generally takes less than an hour from the start of intense straining to the delivery of the lamb. Time to delivery of lambs is approximately 30 minutes or less for a single lamb and up to 2 hours for triplets. Labor in primiparous ewes may take longer. No preference in time of day to deliver has been observed, but if disturbed, the ewe may stop labor for a few minutes until settled again. Normal presentation of the lamb is described as anterior dorsosacral with front limbs extended and preceding the nose by approximately 6 cm (2 to 4 inches). Also normal but associated with greater risk to the safe delivery of the lamb is posterior dorsosacral with hind limbs extended. If delivery is delayed and the umbilical cord is compressed between the lamb and the pelvis of the ewe, the lamb may suffocate before delivery is complete. After delivery of the lamb, the ewe stands, causing the umbilicus to rupture. The ewe turns and begins to nuzzle and lick the lamb to stimulate breathing and to clean it off.
Induction of lambing can be done if the breeding date is known within an accuracy of 3 days—for example, if breeding was synchronized using hormones and only one breeding opportunity occurred. Ewes will respond to an injection of dexamethasone (16 mg given intramuscularly [IM]) or betamethasone (10 to 12 mg IM) after day 137, but it is preferred to wait until day 142 to ensure good fetal viability. Commonly, producers may wait for the first few lambs to be born and then induce the rest of the pregnant ewes. Lambing generally occurs between 36 and 60 hours after induction. Induction is not associated with an increased risk of retained fetal membranes. In instances of vaginal prolapse or pregnancy toxemia, it may be advisable to induce as early as day 137, with the goal of saving the ewe.
Malpresentation of the lamb (or lambs) may manifest in any of various ways: one or both front limbs retained; head retroflexed; true breech presentation, in which the lamb is in the posterior dorsosacral position but the hind legs are flexed forward; dorsopubic or dorsoiliac position; and in the case of multiple births, presence of multiple limbs or heads, or of more than one lamb, in the pelvis at the same time.
Maternofetal disproportion most commonly occurs when ewes that are carrying singles are fed too well in late gestation. Occasionally the ewe may simply have a congenitally small pelvis, or the disproportion may be the result of mating a small-breed ewe and a large-breed ram.
Poor cervical dilation may be due to vaginal prolapse; improper presentation, position, or posture of the lambs; fetal death before stage 1 labor (e.g., from abortion diseases); or possibly damage to the cervix from chronic exposure to phytoestrogens. Ringwomb is the term used to describe incomplete cervical dilation that is unresponsive to manual dilation. The cervix is hard, as it is before stage 1 labor. This condition occurs more frequently in primigravida lambs but may be seen in sheep of any age. Most flocks experience occasional cases of ringwomb, but outbreaks in which up to 15% of ewes are affected have been described.
The practitioner should ensure that the proper tools and protection are available and that the gloves are well lubricated (see Box 91-1). The uterine wall is friable, so only gentle manipulation is advised. A tear in the uterus leads to peritonitis, which is not well tolerated in sheep.
If extensive manipulation is required, use of an epidural anesthetic procedure is advised. The epidural injection generally is performed at the sacrococcygeal space. After the area is clipped and disinfected, a 20-gauge needle is inserted at an angle of 20 degrees to the tail when held horizontally. Lidocaine hydrochloride is then injected at a dose rate of 0.5 mg/kg of body weight (1 ml of 2% lidocaine/40 kg). Additional analgesia may be obtained by combining xylazine with the lidocaine hydrochloride at a dose of 0.07 mg/kg of body weight (0.14 ml of 2% xylazine added to each milliliter of lidocaine hydrochloride). Adult ewes may range in mature body weight from 60 to 80 kg, depending on breed and maturity. This dosage may cause paresis and ataxia of the hindlimbs for up to 8 hours.
With a retained front limb, if the lamb is small, sometimes it may be extracted by gently pulling with the leg still back. With large lambs, however (or small ewes), it is necessary to correct the limb position before delivery is attempted. It generally is necessary to repulse the lamb gently back into the uterus if possible and then, after tracing the limb from the shoulder and elbow, hook the retained leg below the elbow with a finger, bending the carpus and then the fetlock in order to raise the foot over the brim of the pelvis. The practitioner must take care to protect the wall of the uterus from the foot by cupping the foot in the hand. If the fetus cannot be repulsed or if room in the pelvis is insufficient to allow correction of the position, a cesarean section is indicated if the lamb is still alive, or if the lamb is dead, a partial fetotomy is indicated. Viability is determined by checking for the following: suckle reflex, gag reflex, corneal reflex. If none are present, a partial fetotomy is performed by removing the head and neck to increase room to reposition the leg.
With lateral retroflexion of the head, again, an attempt is made to repulse the lamb in order to increase the available space for correction of the head position. A lamb snare around the head and front limbs can be used to help guide the head around. Traction on the lower jaw is avoided unless the lamb is dead, because this usually will result in a fracture to the mandible. If this maneuver is unsuccessful, cesarean section if the lamb is alive or partial fetotomy if the lamb is dead should be considered.
Maternofetal disproportion may be present concurrently with malposture (e.g., head or limb retroflexion). Once the lamb is in the proper presentation, position, and posture, either soft ropes or the lamb puller can be used to apply gentle traction, ideally to both the front limbs and the head simultaneously. To determine if the lamb can be delivered vaginally, the examiner can assess whether both elbows and the head can be pulled into the pelvis at the same time. Inability to do so with relative ease indicates that vaginal delivery cannot be done safely for the ewe or the fetus. Plenty of lubrication is used to assist extraction. While the lamb is being pulled, after the thorax is clear of the vagina, the lamb is rotated approximately 30 degrees to prevent hip lock.
With poor cervical dilation, the practitioner attempts gentle manual dilation, keeping the hand and arm well lubricated. If after 10 minutes no progress is observed, the problem may be true ringwomb. In this condition, the cervix does not undergo the normal parturient softening. The cervical softening process starts with the prepartal drop in progesterone. This triggers an infiltration of leukocytes, which causes collagen degradation and hence softening. The cause for failure of the cervical softening process is not known. Some success at treatment has been reported with application of an estrogen product or prostaglandin E2α to the cervical area, or with injection of such agents, and followed in a few hours by oxytocin. The alternative is cesarean section.
With uterine torsion, the practitioner must determine the direction in which the torsion has occurred and then either gently flip the uterus around or hold the fetus and have assistants roll the ewe in the opposite direction of the torsion. In approximately 50% of the cases, poor cervical dilation is present even after detorsion has been accomplished. Cesarean section should be considered in those cases.
If uterine inertia is due to hypocalcemia, the ewe is given parenteral calcium before delivery. This is done by slow intravenous administration of 50 to 100 ml of a commercial calcium borogluconate solution, followed by an additional 50 to 100 ml injected subcutaneously.
After delivery of the lamb primarily responsible for the dystocia, oxytocin (30 to 50 IU) can be given (unless the dystocia is due to uterine inertia). After 10 minutes, the vagina is checked for the presence of additional lambs. If uterine inertia is present, both horns are carefully explored to their ends to locate more lambs.
For the left flank only, paravertebral anesthesia to block the T13, L1, and L2 paravertebral nerves is achieved using the following method: The midpoint of the first lumbar process is confirmed by palpation, and a 6-cm spinal needle is inserted 2.5 to 3.0 cm from the midline along a perpendicular line running from the midpoint of the first lumbar transverse process to the spine and at a depth of 4.0 to 5.0 cm. The needle may need to be directed forward to walk it off the front of the transverse process. After the needle is felt to penetrate the ligament between T13 and L1, 4 to 5 ml of 1% lidocaine hydrochloride is injected to block the 13th thoracic nerve. the needle is retracted and an additional 2 ml is injected to block the dorsal branch of the T13 nerve. The needle is then withdrawn and redirected caudally to block L1 and is walked off the back of the first transverse process. Another 4 to 5 mL is given; then the needle is withdrawn slightly and another 2 ml is injected. To block L2, this technique is repeated but just anterior to the second lumbar process.
Surgical technique is standard. If the fetuses are dead, the uterus should be packed off using sterile drapes before an incision is made. After the first lamb is extracted, both horns should be carefully explored to the tip to detect the presence of more lambs. The practitioner should avoid incising any caruncles because this may result in excessive bleeding. After suturing, oxytocin is administered once and parenteral antibiotics are given for 3 to 5 days.
Not uncommonly, a dystocia may not be detected until the lambs have died, or in some instances, have become emphysematous. If the lambs cannot be pulled, a fetotomy is preferred to a cesarean section. If the fetus is emphysematous, the uterus also may be compromised and friable. A subcutaneous fetotomy can be performed using a finger knife to avoid vaginal or uterine damage. Again, oxytocin and antibiotics are given at the completion of the procedure.
Lambs normally will begin to breathe within 30 seconds of delivery. Techniques to stimulate the lamb that is slow to breathe include rubbing the head and thorax vigorously with a dry towel, pouring cold water in the ear, and stimulating the sneeze reflex by tickling the nostrils. Swinging the lamb may help extract fluid from the nose but makes it difficult for the lamb to breathe because of centrifugal pressure on the diaphragm. Mouth-to-nose resuscitation should not be done because of the risk of contracting a zoonotic infection from the lamb, such as Chlamydophila abortus or Coxiella burnetii infection. A technique of inflating the lungs that has been used with some success is as follows: A lamb stomach tube is inserted into the esophagus of the lamb. By means of gentle pressure applied with a thumb and forefinger, the esophagus is closed off distal to the end of the tube. The other hand is used to close off the mouth and nostrils. The clinician softly blows once into the tube. With the esophagus closed off, the air will be forced down the trachea into the lungs. The tube is removed after delivery of one breath, and the lamb is reassessed.