Diagnosis and control of neonatal losses in sheep.

Advances in Sheep and Goat Medicine

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Diagnosis and Control of Neonatal Losses in Sheep Joseph S. Rook, DVM, * Gijs Scholman, IR,t Sheila Wing-Proctor, L VT,t and MaryEllen Shea, BS§

INTRODUCTION

Sheep producers in the United States have traditionally used the practicing veterinarian for advice on individual animal therapy. Except when extremely valuable individual animals are involved, the economic realities of the sheep industry suggest that continuation of traditional veterinary service will have little effect on flock productivity and the economic survival of the producer. At this time, producer use of veterinary services is rather limited. A recent survey of sheep producers indicates that average-sized flocks (40 head or less) use professional veterinary service about three to four times per year. For larger production units (flocks in excess of 100 ewes), there is a similar low level of contact; profeSSional visits in these flocks average just six per year. 27 It would appear that traditional veterinary practice may be inappropriately budgeting disproportionate amounts of labor and resource toward individual animal therapy at the expense of producer profitability. Industry recognition of the veterinary profession's inability to address profitability has, no doubt, triggered this reduced demand for professional service. Management decisions affecting nutritional programs, marketing, perinatal mortality, and the genetic makeup of the breeding flock greatly influence profitability, yet seldom receive input from the veterinary profession. Currently, feed costs account for nearly 80% of the annual production dollar Gordan R. Personal communication), lamb mortality consumes 15% to 20% of the annual lamb crop,8,l1,12,14,23,25 crossbreeding programs regularly allow com-

*Associate Professor, Michigan State University College of Veterinary Medicine, East Lansing, Michigan tResearch Manager, Provimi BV, Nieuwegein, The Netherlands tField Service Technician, Veterinary Clinical Center, Michigan State University College of Veterinary Medicine, East Lansing, Michigan §Computer Analyst, Department of Large Animal Clinical Science, Michigan State University College of Veterinary Medicine, East Lansing, Michigan Veterinary Clinics o/North America: Food Animal Practice-Vol. 6, No.3, November 1990

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mercial flocks to exceed a 200% lamb drop, and annual cyclic market fluctuations of $15 to $20 per hundredweight occur in the market for finished lambs. 19 It would follow that, in most flocks, attention to anyone of these four areas of production could increase producer income by at least 20% to 25%. As previously mentioned, one of the major factors· affecting gross dollar output for the commercial sheep producer is perinatal lamb mortality. However, documentation of perinatal lamb losses in the United States is often limited to individual western range flocks or flocks at test centers or university experiment stations. 8 ,12,23,25 Mortality research from the major sheep-producing countries of the world indicates a regional pattern of perinatal. lamb loss that appears to be influenced by weather, management practices, nutrition, housing, .and genetic factors. Lamb mortality reports consistently demonstrate a pattern of perinatal losses ranging from 10 to 35% of the annual lamb crop. This annual preweaning loss appears to be accepted by many producers as a normal cost of production. Diseases involving neonates usually occur with little warning. The consequences to the newborn are severe, and treatment is commonly unrewarding. Prevention of neonatal losses would seem to be a more feasible alternative to traditional treatment programs. The long-term economic benefit of prevention programs to both the producer and veterinarian should be obvious. However, veterinarians and producers need to recognize where, when, and how lamb losses occur before any preventive programs can be developed. Veterinarians and producers also need to acknowledge the impact of management decisions on perinatal mortality and the economic survival of the producer. Epidemiologic Considerations If any sizable reduction in lamb loss is to occur, it is essential that veterinarians be able to recognize and appreciate the character of perinatal losses, be it because of management considerations, infectious diseases, or both. One study suggests that 70% of all lamb losses are due to management problems, not infectious disease. 14 Although costly laboratory diagnostic procedures are often necessary to isolate a specific organism, the classification of that organism does little to solve basic management problems contributing to the clinical expression of the disease. However, on-the-farm gross post mortem examination can group the majority of preweaning lamb losses into general mortality categories. These crude yet practical mortality classifications can be used to assist the veterinarian in concentrating control measures on documented losses that are known, and not perceived, to affect a given flock. Throughout much of the literature, four broad categories of perinatal lamb loss continually appear: (1) starvation/hypothermia/exposure, (2) stillbirth or stillbirth/dystocia, (3) pneumonia, and (4) abortion. World-wide, these four basic post mortem descriptions categorize more than 50% of documented perinatal losses. 4 ,9,11,12,14,16,19 A 3-year mortality study conducted by the authors demonstrated that hypothermia/starvation, stillbirth/dystocia, abortion, and pneumonia accounted for 87.3% of all preweaning losses during the 1986 Michigan lambing season. In the same study, the 3-year average loss, from 1986 to 1988, due to hypothermia/starvation, abortion, stillbirth/dystocia, and pneumonia accounted for 71.6% of all preweaning deaths.l 9 The importance of these four major classifications of perinatal mortality should be obvious. Table 1 defines the numerous causes of perinatal mortality observed by the authors and may serve as a guideline for practitioners during routine gross post mortem examination. However, space constraints of this publication will limit discussion of perinatal mortality to the previously described four major areas of perinatal lamb loss. Recognizing and recording

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Table 1. Gross Post Mortem Diagnosis of Perinatal Mortality CAUSE OF DEATH

TIME OF DEATH

Starvationfhypothermia

Postnatal

Pneumonia

Postnatal

Neonatal respiratory distress syndrome

Postnatal

Stillbirth

Birth

Dystocia/stillbirth

Birth or recent postnatal

Trauma

Postnatal

CASE DEFINITION

Normallung inHation, lack of milk in the abomasum and/or intestinal tract. Color change in perirenal fat from light tan to a purple gelatinous appearance. Depletion of perirenal, coronary groove, and external thoracic fat. Acute hypothermia in lambs less than 5 hr old may show no fat depletion. The presence of a small amount of serum-colored Huid in the thorax, absence of other pathologic lesions, and manure-stained, worn soles may be all that is noted. Anterior ventral pattern of lung consolidation and firmness, with dark purple discoloration of the affected area. Often unilateral. Dark purple, edematous appearance to the entire lung field, with petechial hemorrhage throughout the lung and pericardium in peracute cases with septicemia. Fibrinous adhesions, pleural effusion, and lung abscesses commonly observered in chronic cases. Incomplete lung inHation, diffuse patches of atelectasis intermixed with patches of normal inHated lung. Pronounced alveolar definition. Lambs less than 1 week old. Full-term lambs displaying total lung atelectasis. Lungs are a dark purple color, with no pink, spongy areas of inHation. Fresh umbilical cord, meconium-stained Heece, soft rounded nonstained feet, or attached placental material suggest recent birth. Often identical to stillborn lambs with added evidence of dystocia traumalocal edema (head, forelimbs, perineum, tail), meconium staining, fractured ribs, ruptured liver and abdominal hemorrhage, fetotomy, reported caesarian birth, or emphysematous fetus. Recent postpartum deaths will exhibit similar lesions with inflated lungs and, often, multiple causes of death. Trauma-related hemorrhage in the stillborn lamb usually appears as unclotted blood. Hemorrhage occurring postpartum will usually be clotted. Nondystocia-related evidence of fractured ribs, hemothorax, lacerated lung, ruptured liver, hemoperitoneum, fractured limbs, suffocation, blood loss due to castration or docking, or history of trauma. ( continued)

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Table 1. Gross Post Mortem Diagnosis of Perinatal Mortality (Continued) CAUSE OF DEATH

Overeating disease Type C TypeD

TIME OF DEATH

Early postnatal Late postnatal

Intestinal blockage

Partum/ postnatal

Urethral calculi

Postnatal

Spider lamb syndrome

Prenatal/ birth/postnatal

Arthrogryposis/ hydranencephaly


Septicemia


Omphalophlebitis (navel ill)

Postnatal

White muscle

Postnatal

Scours

Postnatal

Abortion


Other causes


Unknown


CASE DEFINITION

Milk-engorged abomasum and small intestine, with petechial and ecchymotic hemorrhage. Prior to 1 week of age. Petechial and ecchymotic hemorrhage or purple discoloration of the intestine. No evidence of volvulus, intussusception, or torsion of the bowel. Lambs usually older than 3 weeks of age, unless on milk replacer. Purple bowel discoloration to the affected area with evidence of blockage, volvulus, torsion, or intussusception. Intestinal strangulation through abdominal hernias or congenital deformities. Bladder or urethral rupture; calculi present. Urine in the peritoneal cavity or subcutaneous fascia of the abdomen. Gross angular limb deformities and/or face and spinal deviations consistent with congenital chondrodysplasia. Arthrogryposis in combination with hydranencephaly, micromyelia, hydrocephalus, and/or cerebellar hypoplasia. Petechial hemorrhage or diffuse multifocal abscess formation on the heart, kidney, spleen, liver, and/or lung; or fibrinous exudate noted in the pericardial fluid, in absence of other gross findings. Liver abscess formation and/or associated peritonitis and/or joint infection originating from the umbilical vessels. Variable and grossly apparent pale discoloration of the muscles. Not associated with blood loss. Feces-stained buttock, thighs, and tail. Distended, fluid-filled intestine, with hemorrhage and inflammation of the intestinal lining. Secondary peritonitis occasionally noted. Prepartum fetal expulsion. Premature fetal size, prepartum fleece, or fetal mummification. Also, weak or stillborn lambs are associated with an abortion outbreak. Other diseases such as polioencephalomalacia, dock infections, tetanus, and copper toxicity. Individuals that do not fit in any of the previous categories.


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these four major areas of lamb loss during a given lambing season will ali ow the producer and veterinarian to assess and rectify management decisions contributing to Hock loss patterns. Veterinarians should avoid unwarranted concern about individual necropsies that do not fit into a given post mortem category, unless numerous losses are occurring with similar post mortem findings. Veterinarians should also caution producers that it is usually difficult to initiate management changes that dramatically affect lamb losses during the same lambing season. The onslaught of mortality early in life and the significant contribution of management factors to perinatal mortality underscore the need for prevention, versus treatment. Progressive producers and their veterinarians should be willing to employ individualized Hock mortality information for the purpose of consolidating disease control measures. Lamb mortality surveillance by various authors indicates that proportionate loss due to anyone of the four major causes of perinatal mortality can vary greatly between Hocks, between geographic areas, and from season to season. In a recent 3-year mortality study involving Michigan Hocks, hypothermia and starvation accounted for as much as 49% of the preweaning mortality in some Hocks or as little as 2% of the mortality in others. Similar single-season variations in the magnitude of pneumonia, abortion, or stillbirth losses existed for individual Hocks. 19 In the same survey, individual Hock variations in total perinatal mortality (due to all causes of death) Huctuated between 5% and 35% of the yearly lamb crop.19 The Michigan average preweaning lamb loss figure of roughly 15% to 20% of the lamb crop was very similar to that reported by other investigators. 4,6,11,16 However, some producers consistently limited preweaning mortality to the 5% to 6% level. 19 Reducing perinatal mortality from 15% to 20% of the lamb crop to a 5% level should be a realistic goal for every veterinarian and producer. Although post mortem diagnosis of perinatal mortality is the only accurate method of documenting losses in a particular Hock, mortality investigations in the United States would indicate that, as a group, sheep producers experience very similar problems to those that occur in other parts of the world. Exceptions to these trends generally include selected western range Hocks that encounter increased losses due to predators 25 _and bacterial scours. 8 A 1986 -1988 mortality study by the authors examined 2655 perinatal lamb deaths occurring in 28 Michigan Hocks. 19 Figure 1 illustrates the grouping of perinatal losses into the four major categories of (1) dystocia/stillbirth, (2) starvation/hypothermia, (3) pneumonia, and (4) abortions. Figure 2 further defines the lamb loss pattern in the same population of Michigan sheep using the definitions listed in Table 1. From Figure 2 it should be obvious that, as a profession, we often emphasize areas of research and education that appear to have minimal impact on perinatal mortality. In addition to recognizing the range of perinatal losses in the sheep industry, it is important that practitioners appreciate the interval at which the majority of perinatal losses occur. The consensus of mortality information illustrates a concentration of perinatal mortality prior to 3 weeks of age. The literature generally incriminates the first few days of life as a critical period of loss in most production systems. 4,12,14,19,26 The standard classifications of prenatal, natal, and postnatal mortality (Fig. 3) usually indicate that the majority of lamb losses occur in the early postnatal period. 6,11,16,19,26 This statistic should alert veterinarians and producers to the reality that many of the lambs ending up on a pile behind the barn were born alive and had the opportunity for survival.

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Other 27%

843

Stillborn/Dystocia 20%

Starvation/ Hypothermia 19°",

Pneumonia 17% Figure 1. Categorization of the gross necropsy findings on 2655 lambs examined during the 1986 -1988 lambing seasons. These lambs originated from 28 Michigan fLocks. Lambs that died of multiple causes are included in more than one category.

Further categorization of postnatal losses, in Michigan lambs, illustrates a significant clustering of mortality during the first 3 weeks of life (Fig. 4). Closer inspection of the data localizes a wave of postnatal mortality that crests during the first day and first week following birth. 19 The literature would indicate that this is a common occurrence in most of the sheep-producing countries of the world. 9,12,16,21,24,25 The fact that major mortality occurs very early in life is an important concept for producers and their veterinarians to comprehend. The flaw of assaulting perinatal mortality using a classical needle and syringe approach should be obvious. Furthermore, the lamb mortality data presented earlier reflect the role of noninfectious causes in lamb loss patterns. Admittedly, infectious agents are present when mortality occurs, but infectious agents are often secondary and opportunistic to management-related problems. Major lamb losses do occur during the first week of life. Environment in the lambing barn, disease prevention programs, gestational and lactational nutrition, genetic selection, maternal behavior, available labor, and other management practices presumably play important roles in preventing or contributing to perinatal mortality. Post Mortem Examination of the Lamb Realistically, gross post mortem examination performed by the local veterinary practitioner is the only economic means of confirming the cause of perinatal mortality. Practitioners should stress to clients the importance of examining every dead lamb so that flock mortality trends can be noted. Submission of every lamb carcass to a state diagnostic laboratory is usually cost-prohibitive. Local veterinarians need to view the diagnostic laboratory as a support facility for more complete identification of persistent or undiagnosed flock problems, not as a source for routine post mortem examination. Veterinarians should strive to classify losses into generalized categories that will serve to direct an individualized flock control program. All veterinarians and farm personnel, especially women of child-bearing age, should exercise caution when handling dead lambs and placentas. This is especially important when abortion outbreaks are being investigated.

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DIAGNOSIS AND CONTROL OF NEONATAL LoSSES IN SHEEP

Dystocia/Stillborn Starvation/Hypothermia Pneumonia Abortion Trauma Neonatal Resp. Distress Syn. Peritonitis/Liver Abcess White Muscle Disease Unknown Other Congenital Defects Scours Intestinal Blockage Over Eating Disease Septicemia Unknown Other Arthrogryposls/ Hydranencephaly Spider Lamb Syndrome Urethral Calculi

o

5

10

15

20

25

Proportionate Mortality Rate Figure 2. Proportionate mortality rates of perinatal loss involving 2655 lambs examined during the 1986 -1988 lambing seasons.

Table 1 brieHy describes the common lesions noted during post mortem examination of Michigan lambs 19 and can be used as a guide for categorizing lamb losses. The following checklist will also provide direction during routine necropsy examination:

(1) Record the weight of every lamb that is necropsied. Lambs with low birth weights chill quickly and are extremely susceptible to hypothermia. 10,21,22,24 A flock pattern of low death weights in 1- to 3-day-old lambs may indicate an underlying nutritional problem during late gestation. Also, older lambs dying of starvation often weigh less than flockmates of a similar age, or even less than the average flock birth weight. (2) Closely examine the external surface of the lamb. Many newborn lambs thought to be stillborn actually died from hypothermia and/or starvation. True stillborn lambs are coated with a thick clear-to-yellow-orange mucus. They have a fresh-appearing umbilical cord and are often covered with placenta. A mucous covering of bright greenish yellow or orange (because of meconium staining) suggests dystocia. (3) Examine the feet and navel of all lambs. Stillborn lambs have soft,

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pre par tum 510

unknown 17

postpartum 1507

Figure 3. Classification by time of death of 2655 lambs examined during the 1986-1988 lambing seasons.

rounded, clean soles. A lamb that was strong enough to stand after birth will have worn, hard, manure-coated soles. The umbilical cord usually begins to dry and shrivel up by day 2 or 3 after birth and falls off at about day 7 through 10. The feet and umbilical cord provide important clues to the age and strength of the lamb. (4) Perform routine necropsies on all lambs. What the producer believes to be the cause of death is often incorrect. Many lambs die from multiple causes. A necropsy should be performed on all lambs from the same perspective, and a routine approach should be developed that suits the operator. Examining the lamb in right lateral recumbency has proved advantageous for the authors. Disarticulation of the entire left front limb from the thorax often reveals traumatized ribs or depletion of fat covering the external thorax (Fig. 5). These indicators of lamb mortality can go unnoticed if this area is not closely observed at the time of necropsy. (5) Examine the organs of the chest, checking for lung inflation. The lungs of stillborn lambs will be a dark purple-red color, similar to that of a liver, consistently throughout (Fig. 6). Normally aerated lungs are pink and spongy to the touch. Variations in consistency and color within the same lung field may indicate pneumonia. Lambs that have died from pneumonia usually exhibit the common anterior-ventral orientation of lung lesions typical of inhalation-type pneumonias (Fig. 7). Lambs with chronic pneumonia may demonstrate lung abscesses and adhesions similar to those observed in bovine shipping fever. It is important to examine both right and left lung fields. Typically, the right anterior lobes are most affected. Removal of the pericardial sac often reveals reduced fat in the cardiac groove (starvation) or petechial epicardial hemorrhage and/or fibrin in the pericardial fluid (both signs of septicemia). The thoracic cavity should be examined for evidence of hemorrhage, and the parietal surface for evidence of trauma to the ribs (Fig. 8). (6) Examine the surface of the liver for evidence of trauma or abscesses. Postpartum trauma to the liver commonly causes hemorrhage, which is evidenced by large blood clots attached to the parenchyma of the liver. Natal trauma to the liver often leads to stillbirth and generally results in free, unclotted hemorrhage in the abdomen. Ascending infection of the umbilical vessels may cause large, multiple liver abscesses. Vibrionic (Campylobacter) abortion

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Number of Lambs

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Days of Age

Figure 4. A, The concentrated postpartum loss that occurs during the first 3 weeks following birth. B, The major wave of postpartum mortality that occurs during the first few days of life. Both graphs represent perinatal losses documented during the 19861988 lambing seasons.

may also create small, tan, doughnut-like necrotic lesions (Fig. 9) on the liver, and the liver may appear swollen. (7) Is there milk in the abomasum and throughout the intestines? Prior to nursing, normal newborn lambs have a very large abomasum distended with clear, amber mucus (see Fig. 6). The absence of milk in the stomach and intestine is a common finding in lambs that have died of hypothermia and starvation (Fig. 10). Suckled milk normally bypasses the forestomachs and proceeds directly to the abomasum, where curdling occurs as part of the digestive process. Weak lambs tube-fed by producers shortly before death

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Figure 5. A, Normal amount of external fat covering the ribs of a stillborn lamb. B, Fat depletion in a lamb that died of starvation. (From Rook IS: Why didn't it live? The Shepherd 34:26-27, 1989; with permission.)

often have fluid milk in their stomach and upper duodenum. Therefore, starvation should not be ruled out simply by the presence or absence of milk in the abomasum. The lamb in question may not have survived for a long enough time after tubing to allow the milk to clot and digest. The presence of large amounts of hay or silage in the abomasum may also help support a diagnosis of starvation. (8) Is perirenal fat present in the normal amount and color? The color and consistency of the perirenal fat is extremely helpful in the diagnosis of hypo-

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Figure 6. NoninHated lung, mucus-distended abomasum, and large amount of tan perirenal fat typical of a stillborn lamb. (From Rook IS: Why didn't it live? The Shepherd 34:26-27, 1989; with permission.)

Figure 7. Classic pathology of pneumonia, observed in a 2-day-old lamb. (From Rook IS: Why didn't it live? The Shepherd 34:26-27, 1989; with permission.)

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Figure 8. Traumatic fractures of the ribs secondary to starvation. Note the loss of perirenal fat and lack of milk in the abomasum and intestines of this 3-day-old lamb. (From Rook JS: Why didn't it live? The Shepherd 34:26-27, 1989; with permission.)

Figure 9. Doughnut-shaped necrotic lesions of the liver that are usually associated with vibrionic abortion.


543

thermia and starvation. Practitioners should pay particular attention to the color and amount of perirenal fat typically found on stillborn lambs (see Fig. 6). This so-called tan fat is the primary pre suckle source of energy. As starvation ensues and perirenal fat is consumed for energy, this light tan fat changes to a dark purple, gelatinous-looking color ar.d consistency (Figs. 10 and 11). If starvation continues, the perirenal area becomes devoid of fat. Lambs born in severe cold and dying of simple hypothermia will not survive for a sufficient time for these fat changes to be observed. During extreme hypothermic stress, normally inflated lungs, wear to the soles of the feet, and lack of milk in the abomasum may be the only gross postmortem findings. Practitioners should be cautioned that the lack of classical infectious lesions often supports the diagnosis of hypothermia and starvation. Lambs thus affected should not be placed in the unknown category. Lambs that do survive for several hours or days after birth will exhibit variations in the amount and color of perirenal fat. Practitioners should also be cautioned to check perirenal fat on every dead lamb on which a necropsy is performed. Many lambs that the authors have examined by necropsy have died from multiple causes (see Fig. 8). Lamb starvation commonly underlies many of the infectious diseases diagnosed at necropsy. Its recognition as a flock problem is essential. (9) Examine the remainder of the abdominal cavity for other common problems. Infections of the intestinal tract are often difficult to detect, and a gross diagnosis of scours may do little to determine the causative agent and appropriate therapy. Regardless of the causative agent, discolored, fluid-distended intestine is commonly the only necropsy lesion noted in lambs affected with scours. Knowledge of flock housing and environment, previous flock history, duration of the scours, and age of the affected lamb are all helpful in arriving at a tentative diagnosis. Escherichia coli scours usually affect lambs during the first

Figure 10. Typical postmortem findings in a lamb that died of starvation and hypothermia. Note the inflated lungs, absence of milk in the intestinal tract, loss of perirenal fat, and appearance of wear on the feet. The ribs were fractured during the postmortem examination, and color variations on the lung surface were due to postmortem changes. (From Rook JS: Why didn't it live? The Shepherd 34:26-27, 1989; with permission.)

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Figure 11. Progressive loss of perirenal fat commonly observed in lambs that died of starvation and hypothermia. The kidney in the upper left is totally covered with tan perirenal fat. which is normal for a stillborn lamb born to a well-fed ewe. Total depletion of perirenal fat can be observed around the kidney on the far right. The amount of depletion and intensity of color of perirenal fat increase as one views the kidneys from top to bottom and left to right. (From Rook JS: Why didn't it live? The Shepherd 34:26-27. 1989; with permission.)

week of life, whereas scours resulting from coccidiosis generally occur in lambs older than 3 weeks. Peritonitis often follows recovery from scours and navel ill. Localized areas of dark purple bowel may indicate intestinal obstruction from torsion, volvulus, or intussusception. The author (JSR) has commonly observed these lesions in lambs reared on artificial milk replacer. Caution should also be taken to not confuse the discolored bowel commonly observed with intestinal displacements with similar bowel discolorations observed in lambs affected with overeating disease. Postcastration hemorrhage or urine from a ruptured bladder may also be detected in the abdomen. A FLOCK APPROACH TO PERINATAL MORTALITY Prevention of Neonatal Losses Due to Hypothermia, Starvation, and Exposure World-wide, hypothermia, exposure, and starvation are incriminated in roughly 25 to 50% of all preweaning lamb losses. 5 ,9,I1,16,19,25 It is the authors' experience that hypothermia and starvation account for nearly 30% of all preweaning lamb losses in Michigan Hocks and 50% of all postpartum losses that occur during the first week of life. 19 Figure 12 illustrates that the majority of hypothermia and starvation losses in Michigan occur prior to 3 weeks of age, with a major peak occurring during the first 3 days of life. Management practices greatly affect mortality resulting from hypothermia, exposure, and starvation. In large commercial Hocks, where lamb losses

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Number of Lambs 500~----------------------------------------------'

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3 4 Days of Age

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Figure 12. A, The concentration of hypothermia and starvation losses during the early postpartum period. B, The losses that occur in the first week after birth. Data generated from 2655 postmortem examinations performed during the 1986-1988 lambing seasons.

average 15 to 20% of the lamb crop, hypothermia and starvation may account for as much as 49% or as little as 2% of the perinatallosses.1 9 A basic understanding of hypothermia, exposure, and starvation is necessary if management's role in prevention is to be appreciated. Starvation and/or hypothermia can lead to the demise of newborn lambs through two distinctly different pathways. During the first several hours following birth, newborn lambs have a relatively high plasma concentration of glucose and initially do not suffer from simple starvation. Lambs are born with glycogen and fat reserves that vary in accordance with the nutritional status of

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the ewe. l In warm weather, lambs born to a well-fed ewe can survive for up to 4 days without supplemental nutrition. Severe weather stress, however, may create a 500% increase in demand for energy and deplete the energy reserves of the newborn lamb within 6 to 16 hours.2 Much of the scientific literature dealing with hypothermia, exposure, and starvation originates from the United Kingdom, Australia, and New Zealand. The weather conditions confronting the majority of winter lambing producers in the" United States are, most likely, more severe than that experienced by producers in those countries. The physiologic phenomenon taking place during the first 0 to 5 hours of life is, for the most part, an excessive loss of body heat coupled with reduced heat production. 7 At this crucial time in the newborn's life the major catalysts for excessive heat loss and reduced heat production include (1) exposure to climatic factors, (2) evaporative heat loss due to a wet birth coat, (3) small body mass, (4) reduced mobility leading to reduced heat production, (5) dystocia-related hypoxia and subsequent lack of thermoregulation, (6) poor mothering behavior, and (7) lack of colostrum. Rectal temperatures in cases of mild hypothermia range from 99 ° to 102°F, and in severely hypothermic lambs thermometer readings often plunge well below 97°F, until death ensues. The author (JSR) has observed hypothermic lambs that were not yet recumbent with rectal temperatures in the range of 84 ° to 90°F. It is important that the veterinary practitioner stress the relevance of using rectal temperature as a guide to the identification and treatment of hypothermic lambs. Inexpensive electronic digital thermometers are a useful tool for the producer. They are less likely to break, easy to read, and usually will record extremely subnormal rectal temperatures. Although supplemental nutrition is important for the hypothermic newborn lamb, producers should be made aware that colostrum administered through a stomach tube is not the primary component of a treatment program within the first 5 hours following birth. Treatment regimes should stress supplemental heat to reverse the excessive loss of body temperature. Uncomplicated starvation generally affects newborn lambs that survive the critical 0 to 5 hours following birth, when hypothermic deaths are most common. Mortality in these older lambs results from starvation-induced hypothermia. Starvation, and the subsequent lack of energy needed to produce body heat, is the primary pathway leading to terminal hypothermia. These older lambs exhibit extreme depletion of body fat stores and severe hypoglycemia. 7 The starvation-associated hypoglycemia commonly observed in older lambs must be addressed by the veterinarian and producer if a treatment regimen is to be successful. The sudden warming of a hypoglycemic lamb can lead to cerebral hypoglycemia and death. 7 Correction of starvation-induced hypothermia in older lambs needs to address the triad of hypoglycemia, hypothermia, and starvation. Inadequate heat production due to starvation becomes a cyclic affair. As Stafford and Hoversland23 note: "Cold increases the effects of undernutrition by putting greater demands on the animal's energy resources, so accelerating death from starvation. Conversely, starvation exacerbates the effects of cold by reducing or limiting the heat production capability of the lamb, making death from hypothermia more likely. As a result, the urgency with which a newborn lamb requires to begin suckling to replenish its energy reserves is greatly magnified in cold weather." Treatment for hypothermia, exposure, and starvation will vary according to the age of the lamb and the rectal temperature of the affected individual. A treatment scheme was developed at the Moredun Research Institute in the United Kingdom to address the issue of hypoglycemia. 7 For mild hypothermia (99 to 102°F) at any age, the following steps are indicated: 0


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1. Move ewe and lamb to shelter, or remove lamb from the ewe. 2. Towel-dry wet lambs to prevent chilling due to evaporation; supplement with warm dry heat (100° to 103°F maximum temperature). 3. Tube feed colostrum at the rate of 20 to 25 mL per pound of body weight (IBO to 200 mL per 9 to 10 lb lamb). 4. Return to ewe when rectal temperature is normal (usually 1 to 3 hours). 5. Assure future nutrition and warmth. 7 For severe hypothermia (below 99°F) in lambs under 5 hours old, the treatment is the same as for mild hypothermia. For lambs over 5 hours old, the following steps are indicated: 1. Towel-dry wet lambs to prevent chilling due to evaporation. 2. Prior to warming, inject into the peritoneal cavity 5 mL of a 20% dextrose solution per pound of body weight. Hold the lamb from the front legs in a hanging position and inject the dextrose solution (40 to 50 mL for an average-sized lamb) intraperitoneally using a 20-gauge, I-inch needle. Place the needle 0.5 inch beside and 1 inch behind the navel, and direct the needle toward the rump. Disinfection of the site and prophylactic antibiotics are desirable. 3. Warm in a warming box (a plywood box with hand-held hair dryer inserted through a hole in the lid works well) using moving air at a temperature of 100 ° to 103 °F . Avoid overheating by affixing a thermometer to the inside of the box and checking the thermometer regularly. The box dimensions suggested by the Moredun Institute measure at least 1.5 m square by 1 m high. Check the lamb's rectal temperature every 30 minutes. The lamb can be removed when the rectal temperature reaches 99°F. 4. Administer colostrum at the rate of 20 to 25 mL per pound of body weight, after removal of the lamb from the warming box. 5. If only one of a set of twin lambs is involved, remove both lambs from the ewe while warming is taking place and return both lambs at the same time. 6. If, after warming, the lamb(s) are strong enough to stand and nurse, return them to the ewe in a sheltered area. 7. Recognize and correct the initial problem (mastitis, agalactia, environmental problems, mismothering, poor nutrition to the ewe, etc.) to prevent a recurrence. B. Weak lambs unresponsive to initial treatment should not be returned to the ewe. A separate intensive care area should be provided, allowing assurance of isolation, warmth, and nutrition. 7 Producers should be encouraged to weigh the cost of the labor involved with treating unresponsive lambs and realistically decide if extended treatment is productive or counterproductive to overall Hock economics. Continued individualized attention to nonresponsive lambs may usurp precious time and energies better suited for other new arrivals. Farms that experience excessive losses due to hypothermia, starvation, and exposure traditionally have very similar management problems. It is often difficult to prevent these losses in the same lambing season because underlying causes are often rooted in management decisions that occurred prior to lambing. Veterinarians working with producers to reduce neonatal losses at a Hock level should pay particular attention to the following nutritional and management factors. Nutritional Factors. Inadequacies or excesses in the gestational nutrition of the ewe Hock have major implications in losses due to starvation, exposure, and hypothermia. As ewes are removed from fall pastures and placed on stored feeds, the greatly increased nutritional demands of late gestation and lactation

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are often not satisfied. The developing fetus competes for rumen space, while the ewe's ability to ingest large amounts of poor-quality forages declines. If certain nutritional adjustments are not initiated, the poor-quality free-choice grass hays, which had been sufficient during early gestation, can contribute to a negative energy and protein balance during late gestation. Marginallate-gestational nutrition results in small, weak newborn lambs at high risk of hypothermia, exposure, and starvation. 15,21,24 The effect of inadequate gestational nutrition on reduced birth weights is often compounded in high-producing Hocks, in which numerous twin and triplet births occur. Producers and veterinarians should be made aware that twins and especially triplets are considered at high risk of hypothermia and starvation. 7, 10 During regular Hock visits, veterinarians should encourage producers to visually assess ewe condition. Shearing 4 to 6 weeks prior to lambing and condition scoring of ewes throughout gestation are excellent management tools for the assessment of body condition. As an outside observer, the veterinarian can often detect loss of condition that frequently would go unnoticed by the producer. The first 10 lambs born each year should also be weighed. If birth weights are not reasonable for that particular breed of sheep, address the problem by increasing the concentrate fed to the remaining pregnant ewes. Increasing the amount of concentrate fed to Hocks experiencing lambs of low birth weight often assists producers with marginal feeding programs. However, producers should be reminded to address nutritional problems the following fall with forage quality assessment, ration evaluation, and follow-up condition scoring. Producers who follow the standard feeding recommendations listed in many sheep publications and extension bulletins will very nearly meet the nutritional requirements of the ewe, if high-quality forages are used for late gestation and lactation diets. However, it is the authors' experience that very few of the large commercial sheep producers in their area feed exceptionally high-quality forages. Grass and mixed hays in the 7% to 12% crude protein and 45 to 52% total digestible nutrients (TDN) ranges are commonly fed, as are untreated corn silage and occasionally other high-moisture small-grain silages or small-grain hays. Sheep ration recommendations for a 160-lb commercial ewe carrying twins typically suggest an early gestation ration consisting of 3.5 to 4 lb of medium-quality hay. Late gestation rations consist of 3.5 to 4 lb of mediumquality hay and 1 lb of shelled corn, followed by a lactation ration consisting of 4.5 lb of good-quality hay and 2 to 2.51b of shelled corn. These ration suggestions are usually appropriate if the protein in the gestational hay exceeds 9% crude protein and the protein contained in the lactational hay surpasses the 16% crude protein level. The graphs in Figure 13 illustrate the fallacies of following similar standardized feeding practices when forage quality is below these levels. In Figure 13 the early gestation diet (EG) and the late gestation diet (LG) utilize grass hay that was analyzed at 8.1% crude protein and 52.9% TDN. The early gestational diet consists of 3.5 to 4 lb of this hay, and the late gestational diet consists of 3.5 to 4 lb of the same hay plus 1 lb of shelled corn. The lactational diet (L) utilizes 4 to 4.51b of mixed hay tested at 10% crude protein and 55.2% TDN and 2.5 lb of shelled corn. According to National Research Council guidelines for a 154-lb ewe, the levels of crude protein provided by the preceding rations are 10% deficient for early gestation, 26% deficient for late gestation, and 42% deficient for a ewe nursing twins. Similarly, the energy levels are 12% deficient for late gestation and lactation. Comparable nutritional imbalances often exist for other components of the ration. These issues

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T.D.N. (lbs)

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Figure 13. Standardized rations that are not adjusted to forage quality often create deficiencies in energy and protein during gestation and lactation. This example includes a standard early gestation (EG) ration of 3.5-4 lbs of grass hay (8.1 % crude protein and 52.9% total digestible nutrients [TDN]), a standard late gestation (LG) ration of 3.5-4 lbs of grass hay and 1 lb of shelled corn, and a standard lactation (L) diet of 4 - 4.5 lbs of mixed hay (10% crude protein and 55.2% TDN) and 2-2.5 lbs of shelled corn. A, A comparison of the amount of TDN provided by the standardized ration with National Research Council requirements for a 154-lb ewe rearing twins. B, A comparison of the amount of crude protein provided by the standardized ration to the National Research Council requirements for a similar ewe. The deficiencies in energy and protein during early gestation, late gestation, and lactation are obvious. For this example, the breeding and maintenance (main) rations have been described as adequate.

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stress the need to address forage quality through testing and ration evaluation on a regular basis. Lactational nutrition of the ewe flock also contributes to hypothermia and starvation losses. Dietary energy is often sufficient to maintain a healthy-appearing lactating ewe; however, protein deficiencies may greatly reduce milk production for her lambs. Protein deficiencies are very common where ewes are expected to milk for twins. Poor-quality hays, haylage, or caramelized silage, and reliance on unsupplemented corn silage as a "complete feed" for lactation often create deficiencies of 25% to 50% in crude protein. Forage analysis and sound ration evaluation work well to identify problems often not visible to the producer. Producers experiencing later starvation losses (1 to 3 weeks of age) and pneumonia/starvation combinations, especially in twins, should seriously attempt to identify nutritional deficiencies affecting the lactating ewe. Vitamin E and selenium levels in the ewe's diet also appear to contribute to starvation, hypothermia, and pneumonia problems. Producers need to realize that vitamin E and selenium are integral parts of muscle function and the immune system. Improperly functioning tongue muscles and the muscles of swallowing may directly contribute to starvation and aspiration pneumonia. Ewe diets require vitamin E and selenium on a daily basis. Adequate serum selenium levels in the ewe are reflected in the fetus at birth. Ewes receiving appropriate supplemental selenium in the diet quickly deplete selenium levels when the dietary source is removed. This is an important concept to recognize, because oral selenium supplementation needs to be on a daily basis. In Michigan, most commercially available sheep salt or mineral preparations with selenium still elevate serum selenium levels to only one half to two thirds of the levels recognized as desirable. Vitamin E, however, is passed to the lamb not through the placenta but through the colostrum that is ingested shortly after birth. Serum vitamin E levels in ewes grazing adequate pasture are usually sufficient. However, as ewes enter dry-feed and silage programs late in pregnancy, the serum level of vitamin E often drops at a most inopportune time. As with selenium, vitamin E needs to be supplemented on a daily basis. A ewe with subnormal levels of vitamin E will not pass enough vitamin E on to the lamb in her colostrum. Management Factors. Hypothermia and starvation are influenced by many and varied management factors, generally involving the following items. Poor protection from environmental conditions is a problem on many large farms. Cold housing systems need to address wind chill, humidity, ventilation, and crowding factors to arrive at a suitable building that gains some heat from the enclosed animal units but not at the expense of air quality. Lambs can withstand cold once the initial drying and nursing are completed, as long as drafts are not excessive and nutrition is assured. Quantity and quality of help greatly affect starvation and hypothermia problems. The fact that most lambs die on the first day and during the first week of life should suggest to producers that concentrating management practices and labor on these lambs can be a major means of reducing mortality. Feeding systems and lambing facilities need to be efficient, maximizing the time that producers can spend with newborn lambs. Ewes need to be placed in lambing jugs as soon as lambing occurs, to minimize mismothering with other lambing ewes. This is commonly a problem in flocks in which producers work at outside jobs or an illness to the producer occurs during times of heavy lambing. Farms with histories of severe hypothermia and starvation losses often have absent producers for the majority of the day. There also appears to be a certain number of sheep that each individual


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producer can efficiently handle. Larger Hocks, with one major producer and 400 to 500 ewes lambing in three scattered barns, may need to split the lambing season to concentrate a reasonable number of ewes into one locale. Reducing ewe numbers in a given lambing group, separating lactating and pregnant ewes, or palpating udders and grouping ewes all help concentrate observation for signs of lambing or sick animals. Observation is more efficient. Feeding is also more efficient. Producer recognition and early assistance to difficult lambing ewes also reduces the number of hypoxic lambs that are unable to thermoregulate. Lambing pen and nursery areas greatly affect hypothermia and starvation problems. Producers who have sufficient numbers of lambing pens, and use them, generally have much lower losses. As a rule, one lambing pen for every three to five ewes is sufficient. Producers lambing later in the year, when most of the ewes have cycled and bred during one heat period, usually need one pen for every three ewes. Ewes and lambs should remain in lambing pens for 3 days, until maternal bonding has taken place. This also facilitates producer observation. Routine procedures such as docking, castrating, and vaccinating should be done on day 2 to allow observation and adjustment for at least 24 hours before lambs and ewes are placed in smaller group pens. Small group pens of three to ten ewes for 2 days after removal from the lambing pens help to reduce confusion and mismothering before final turnout. It is surprising how few lambing pens and nursery areas many producers have and use. No identification linking ewes to their lambs is also a problem in some Hocks. Older unthrifty lambs or lambs that have gotten out of lambing pens cannot easily be traced back to an individual ewe. Starvation usually ensues and the cause (mastitis, for example) goes undiagnosed. Full Heeced ewes also contribute to hypothermia and starvation problems. Many producers still resist shearing prior to lambing. Shearing facilitates nursing by making the teats easier to find and cleaner. Shorn ewes also drag less moisture into the barn and bedding, and the shorn ewe provides body heat to the lamb resting against her. Difficult births are recognized earlier, allowing correction before hypoxia sets in. Lack of milk in individual ewes usually results from mastitis or progressive pneumonia (hard bag). A surprising number of producers recognize that a ewe has no milk, yet are indecisive about removing the lamb and grafting or rearing on milk replacer. During cold weather, a newborn lamb cannot tolerate procrastination. Practitioners should also encourage producers to routinely palpate udders for evidence of mastitis and cull problem ewes. Practitioners and producers need to remember that 50% of all Michigan lambs that were born alive and died during the first week of life died from hypothermia and starvation. I9 Prevention of Neonatal Losses Due to Pneumonia The graphs in Figure 14 illustrate that postpartum pneumonia losses occur over a slightly longer span of time than do hypothermia and starvation losses but still center around the first 3 weeks of a lamb's life. I9 The following management practices appear to be common to Hocks experiencing problems with lamb pneumonia. Overcrowding. On many farms, overcrowding of ewes and their lambs in a confinement situation appears to contribute to increased rates of lamb pneumonia. Flocks experiencing high levels of death loss from lamb pneumonia (30 to 50% of the preweaning death loss due to pneumonia) often show stocking densities in the range of 12 to 13 square feet per ewe. I9 Stocking densities for

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Number of Lambs 250.-----------------------------------------------~

200

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Figure 14. A illustrates the concentration of pneumonia losses during the first 3 weeks of life. B shows the substantial pneumonia losses that occur during the first few days of life. Data generated from 2655 post mortem examinations during the 19861988 lambing seasons.

flocks with low levels of pneumonia typically average 18 to 20 square feet per ewe. 19 For many commercial flocks, a 4 X 4 ft lambing pen represents the least crowded environment that a ewe and her lambs may experience. Adequate natural ventilation of densely stocked cold housing facilities is often difficult if the same facility is expected to be suitable for the prevention of hypothermia. It is the author's (JSR) experience that, in our area, most cold-housed January and February lambing flocks experience minimal losses from pneumonia, even if overcrowded conditions exist. The extremely cold weather typical


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for January and February usually prevents moist humid environmental conditions conducive to the spread of pneumonia. However, extreme temperature and humidity fluctuations (normally found in the transitional months of March and April and occasionally in January and February of mild winters) often initiate lamb pneumonia outbreaks on these farms. As the external air temperature increases, air quality deteriorates as the humidity of barn air increases. When confronted with overcrowded conditions, nonmechanical ventilation systems (which performed well during extremely cold weather) begin to fail. Early winter lambing flocks, by nature of the seasonality of the ewe, usually lamb over a prolonged period of time. Thus, the environmental buildup of pneumonia organisms in the barn, the increased number of lambs in the facility, and temperature fluctuation common during the second half of the lambing season all contribute to a rash of lamb pneumonias that often correspond to the second half of the lambing season. Producers who plan lambing to occur with the onset of pasture grass usually avoid these problems. Exposure time in the lambing barn is minimal, and warmer temperatures allow a maximizing of natural ventilation. The majority of ewes had been cycling during the late fall breeding season, and lambing occurs in a concentrated 3-week period of time. Therefore, environmental build-up of pathogens is minimal, crowding is decreased as lambs and ewes are removed to pastures, and ventilation while on pasture is excellent. As is the case with pasteurella pneumonias in other species, simple stress from overcrowding may also contribute to the disease process in lambs. The physical, nutritional, and psychological stresses associated with lambs trying to locate their dams while competing in overcrowded conditions is enormous. A more sensible stocking density and caution by the producer to avoid excessive moving of ewes and their lambs to new areas and pens can help eliminate stress-related problems. If early winter and early spring lambing flocks experience substantial pneumonia losses, producers need to address the ventilation and overcrowding issue if any real reduction in losses is to occur. It is the authors' opinion that many lambing facilities accumulate heat at the expense of air quality. Adequate nonmechanical ventilation of cold housing systems can often be accomplished by removal of the ridge cap and/or the addition of draft-free side wall openings that can be adjusted to accommodate weather fluctuation. "Chainsaw" construction of side wall openings is often the most practical and economic approach to ventilation problems in cold housing facilities. The incorporation of greenhouse shade cloth into side wall structures (Fig. 15) or over existing sliding doors (Fig. 16) has allowed producers to create a draft-free, dry, reasonably warm, well-ventilated environment for the newborn lamb. With a shade cloth system, existing sliding doors can serve as adjustable openings, allowing the regulation of ventilation. Shade cloth is relatively inexpensive, durable, and flexible in application. Many farms experiencing high pneumonia mortality rates often locate lambing pens in the least ventilated, most protected areas of the barn, with the hope of preventing hypothermia losses. Pneumonia outbreaks often originate in these "deadspace" areas of the facility. Relocation of lambing pens or correction of ventilation deficiencies in these areas is often rewarding to the producer. A simple household fan suspended from the trusses may help to mix air and improve air quality. The overcrowding issue can be addressed by construction of new facilities; however, the economics of construction and the limited usage of most lambing facilities often make this suggestion impractical. A planned division of the flock into two lambing groups of ewes, separated by 3 to 4 weeks, allows maximum

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Pole Barn

Shade Cloth

Figure 15. Application of greenhouse shade cloth to an open side wall in a cold housing system. The material allows air How without draft.

4' plywood or round bales or straw bales

B

Outside sliding door

Shade Cloth

Stationary plywood or plywood attached to gate

Figure 16. Greenhouse shade cloth can also be applied over an existing sliding door that might usually remain closed. A sheet of plywood is placed in the bottom part of the opening, and the shade cloth covers the remainder. The sliding door can be used to regulate ventilation.

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utilization of the facility without overcrowding or additional expense. This also allows for a short break in the barn population before the second group of ewes lamb. Udders on pregnant ewes can also be palpated on a weekly basis and the Hock can be split into close-up and distant lambing groups. The distant lambing group can be housed outside or in a separate, more open facility. Planned outside feeding systems are another way to eliminate total barn confinement and decrease crowding. Moving feeding systems outside increases the amount of barn space available to the lambing ewes. Ewes should be sheared prior to lambing to reduce the amount of moisture returned to the barn and to encourage ewes to come back inside when they are about to lamb. The ewe shorn prior to lambing is also less likely than the full Heeced ewe to drag her lambs outside in severe weather. In winter lambing, the lambing Hock should be restricted to the barn at night to prevent the occasional ewe from lambing outside. The Hock can then be released to the outside early in the morning, before rising temperatures increase barn humidity. Flow-through Systems. The adoption of outside feeding systems in combination with How-through lambing systems (Fig. 1 7) appears to reduce pneumonia problems for many farms. With this type of housing system late gestational pregnant ewes are not allowed to mix with lactating ewes and their newborn lambs. This system reduces crowding in the lambing area and decreases contact of near-term ewes with neonatal diseases such as scours and pneumonia, which typically capitalize on environmental transmission. Flow-through lambing systems also encourage producer compliance with recommended management practices. This division of ewes into production groups facilitates correct and economical feeding practices - either late-gestation or lactation diets can be fed. Producer inspection of the Hock is also simplified by concentrating observation on lambing ewes or sick lambs, but not both. Routine procedures such as docking, castration, and vaccination are encouraged while lambs are in the lambing pens, and a How-through system allows early removal of lactating ewes and their lambs to other facilities. Flow-through lambing systems, in combination with outside feeding, also encourage maximizing ewe numbers with a limited facility. Mechanized feeding of large round hay bales or silage is also facilitated. This mechanized feeding reduces labor and increases producer availability in the lambing barn. Reduced producer comfort, the occasional ewe

Pregnant Ewes Outside Feeding

Lambing Ewes Outside Feeding

Pregnant Ewes

Figure 17. Diagram of a How-through lambing system.

Lambing Ewes

BARN

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that lambs outside, and sporadic wool loss due to frosting of recently shorn sheep are the major drawbacks to this system. Late Gestation and Lactation Diet. Similar to hypothermia and starvation, the nutritional status of the late-gestation and lactation diet often contribute to pneumonia problems. Pneumonia is often secondary to decreased milk production in the ewe and, thus, starvation in the lamb. Correction of energy and, especially, protein deficiencies in the ewe's diet are often major steps toward reducing lamb losses from pneumonia. It is the authors' opinion that Vitamin E and/or selenium deficiencies in the diet of the ewe Hock can also contribute to Hock pneumonia problems. Routine serum sampling of ewes in late pregnancy and liver selenium and vitamin E values from lamb necropsies indicate that many farms in the authors' area have abnormally low levels of selenium and vitamin E, especially at the time of lambing. Gross post mortem examination of lambs originating from farms with above-average losses from pneumonia often demonstrates a right-sided unilateral involvement of the lung in I-to-3-day-old lambs. Most likely, inadequate selenium and vitamin E levels in the newborn lamb affect the muscles involved with suckling, thereby contributing to the aspiration pattern of pneumonia commonly observed in these Hocks. Nutritionally addreSSing the low selenium and vitamin E in these Hocks is an integral part of preventing recurrence of similar problems. Often, low levels of serum selenium and vitamin E occur despite the regular feeding of commercial salt and mineral supplements that are expected (by the producer) to eliminate these problems. Maintaining an adequate level of selenium and vitamin E in the ewe's diet on a daily basis is the only realistic way to assure that newborn lambs are born with adequate selenium and receive adequate vitamin E in the colostrum. If effective commercial supplements are not available to the producer, special formulations may be necessary. Because of the grazing orientation of most Hocks and the common practice of feeding whole home-stored grains, the addition of selenium and vitamin E to the grain mix is usually impractical. Addressing deficiency concerns on a daily basis is most effective through the use of a supplemented free-choice salt mix. Salt and mineral mixes should provide the breeding ewe with 0.7 to 1.0 mg of selenium and 30 to 50 units of vitamin E on a daily basis. Routine serum testing for vitamin E and selenium can be helpful in determining the status of the Hock. Testing ewes just prior to lambing would be most indicative of the status of the ewe at lambing. Realistically, however, most Hocks are checked during the prebreeding fall visit, when rams are tested and ration evaluation for the following lambing season occurs. Veterinarians should use caution in the evaluation of the vitamin E status of the Hock at this time, because most ewes are being grazed on green forages that are high in levels of vitamin E. Most grazing ewes will have adequate serum vitamin E levels while on pasture. However, unsupplemented drylot-housed ewes usually test very low in serum levels of vitamin E. IBR-PI3 Intranasal Vaccine. It is the authors' opinion that the nonapproved use of bovine intranasal IBR-PI3 vaccine and/or commercially marketed pasteurella bacterins administered to ewes or lambs are of limited value in the prevention of pneumonia in newborn lambs. The early onset of pasteurella pneumonia in I-to-2-day-old lambs (see Fig. 7) and the massive lung damage observed at postmortem examination would suggest that vaccination of the newborn with a modified live IBR-PI3 intranasal vaccine or pasteurella bacterin is probably "after the fact." Although this procedure may help prevent PI3 initiation of pasteurella pneumonias in older lambs and ewes, it is the authors' opinion that pneumonia losses in newborn lambs are primarily caused


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by Pasteurella. Initiation of these losses usually occurs before immunity can develop. As is also the case with other species, the development of effective pasteurella vaccines is proving difficult. Injectable Antibiotics. The use of long-acting injectable antibiotics in newborn lambs is a common practice for many producers. The clustering of lamb mortality during the first week of life suggests that infections occur very early in life and are often secondary to starvation, hypothermia, overcrowding, and environmental stresses. The routine use of long-acting injectable penicillin or tetracycline on day 1 and again on day 3 after birth may be warranted in flocks faced with mounting pneumonia losses or flocks whose owners are unwilling to correct management problems. Prevention of Perinatal Losses Due to Abortions Ovine abortion outbreaks are some of the most frustrating problems confronting the food animal practitioner. Mortality surveillance by the authors suggests that in the general population of sheep in our area, abortion accounted for about 16.5% of the preweaning lamb losses experienced by producers. 19 These losses, however, were not evenly distributed throughout the population; instead, they involved severe isolated outbreaks of abortion on individual farms. Abortion outbreaks generally occur during the last 4 to 6 weeks of gestation, when most ewes are at a similar stage of pregnancy. Abortion outbreaks are difficult to diagnose and commonly unrewarding to treat. They are also dissimilar to many of the classical abortion problems that affect cattle and hogs. From a realistic viewpoint, the practitioner should consider some low level of abortion in a sheep flock to be acceptable. If no infectious agents are present, this acceptable, or normal, level of abortion generally stays below a rate involving less than 2% of the ewe flock. Rates that exceed this 2% level of abortion are commonly considered levels for veterinary intervention. When infectious agents are present, abortion levels often involve up to 20% of the lambing ewes. Although numerous infectious agents have been documented to produce abortions in sheep, it is the authors' experience that vibriosis (campylobacterio sis) and toxoplasmosis are most common in our area. Tentative diagnosis of either disease can be made during on-the-farm necropsy of aborted lambs if numerous aborted fetuses and placenta are available. It is important that practitioners encourage submission of multiple fresh samples for diagnosis. This is often not possible when dealing with small flocks, and diagnosis in these cases often involves luck. Ovine vibriosis is transmitted from ewe to ewe by oral ingestion, unlike the classical venereal transmission of bovine vibriosis. In the authors' experience, vibriosis has not been a concern in strictly closed flocks, in which only outside rams enter the farm. Contamination usually occurs with a history of purchased ewes entering the closed system or with the constant movement of sheep in a purebred or commercial flock. Carrier ewes harboring the organism in their manure contaminate the premises. Aborting ewes further spread the organism with the discharge of uterine fluid, aborted fetal material, and placenta. During most outbreaks of vibriosis, aborting ewes show no signs of illness, and abortions occur about 2 weeks prior to the expected lambing date. Occasionally, abortions will not be noted, and only weak, lethargic, newborn lambs that die 2 to 6 hours after birth will be reported. Aborted lambs often appear potbellied because of liver enlargement. The abortion diseases should not be dismissed in cases of stillborn and weak lambs. Post mortem examination may

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reveal a swollen, rounded liver with tan, doughnut-shaped necrotic areas on surface (see Fig. 9). These classical lesions of vibriosis may occur in only 10% to 30% of the necropsied fetuses. Confirmation of vibrionic abortion usually occurs by identifying the organism (either by culture or darkfield microscopy) in a fresh sample of stomach Huid from the fetus. Producers experiencing abortion problems from any cause should be instructed to isolate the aborting ewes and remove the contaminated bedding where the abortion occurred before other ewes try to lick the infected fetus. Practitioners should also advise producers to place the Hock on tetracycline in the feed or water. The authors generally start the Hock on 400 mg of tetracycline per head per day for 2 to 3 days and then reduce the level to 200 mg per head per day. Small Hocks can also be treated with a loading dose of injectable tetracycline and then placed on the oral medication. To prevent further abortions, oral tetracycline should be continued until the majority of ewes have lambed. Vibrionic abortions will usually not affect the same group of adult ewes that experienced vibrionic abortion problems during the previous lambing season. However, replacement ewe-lambs and unexposed adult ewes will continue to be at risk. In any abortion outbreak, practitioners should not wait for laboratory confirmation to initiate tetracycline therapy. Confirmation from diagnostic laboratories often encompasses several weeks of continued abortions, many of which may have been prevented by initiation of oral tetracycline therapy. Most outbreaks of vibrionic abortion respond to oral tetracycline medication, and abortions decrease several days into the treatment regimen. Later lambing groups of ewes should also be considered for vaccination using the ovine strain of vaccine. As a means of prevention, producers whose Hocks are not closed may routinely choose to feed 100 to 200 mg of tetracycline per head per day throughout late gestation. Flocks at risk of vibriosis abortions should also consider vaccination of the ewe Hock prior to breeding and during midgestation. Commercial producers should also be encouraged to seriously consider a closed approach to Hock management. Toxoplasmosis abortions in the ewe flock have become an increasing problem for producers in the midwest. Abortions generally occur during the last 4 to 6 weeks of pregnancy and usually entail the expulsion of mummified fetuses. Abortion of sets of twins and triplets often involves combinations of mummified fetuses and more normal-appearing lambs (Fig. 18). As lambing continues, live term lambs may also accompany mummified fetuses and, as with any abortion disease, weak stillborn lambs. Transmission of toxoplasmosis is usually by oral ingestion of a feed or bedding source contaminated with infected cat feces. The stage of gestation at which a ewe becomes infected and the immune status of the ewe affect the outcome of the disease. 13 Infection of nonimmune ewes prior to breeding or in very late pregnancy produces immunity of the ewe and no clinical disease is noted. The ingestion of infected material by previously unexposed ewes during the first 40 days of pregnancy can result in early embryonic death and fetal resorption. If the rams have been housed with the ewes, a second conception may occur and the ewes may lamb much later in the season than expected. Infection of previously unexposed ewes between 40 and 110 days of pregnancy may result in clinical abortions and mummified fetuses. These variations between the time of exposure and clinical presentation should help the practitioner determine when and by what source contamination occurred. Although fecal contamination of grain storage areas is commonly incriminated as a source of infection, most producers are feeding all-roughage earlygestation rations during the first 40 to 110 days of pregnancy. In the authors'

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Figure 18. Toxoplasmosis abortions commonly produce a mixture of mummified and more normal-appearing fetuses, as in the set of aborted twins in A. B, The surface of the cotyledon commonly exhibits white, granular foci.

area, contamination of the ewe flock during early gestation typically occurs from feeding hay that was infected during barn storage. The history usually involves several litters of kittens being reared in the hay storage area, with the contaminated top layer of hay being fed during 40 to 110 days of gestation. On large confinement operations with multiple hay storage areas, toxoplasmosis abortions may be limited to individual pens of ewes that received hay from specific storage areas. Minimal toxoplasmosis abortion problems have been noted on farms that feed outside-stored large round bales of hay, small square bales stored under outside conditions, or silage. The occasional toxoplasmosis abortions noted on these farms usually entail a suspected straw bedding transmission and involve very limited numbers of abortions. A preliminary diagnosis of toxoplasmosis abortion can usually be made when abortions include multiple mummified fetuses along with more normally developed lambs. Also, inspection of the cotyledon often reveals multiple, localized white foci on the cotyledonary surface (Fig. 18). The visualization of these foci can often be enhanced by fixing the cotyledon in 10% formalin solution. Confirmation of toxoplasmosis generally involves histopathologic demonstration of the organism in the fetal brain or the cotyledon. Serum titers

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from affected ewes may also help support recent infection in the ewe, but are often nondiagnostic because of the lag time between exposure and clinical abortion, and the range of titers often observed in natural outbreaks of the disease. The authors have confirmed the contribution of toxoplasmosis to abortion outbreaks by the use of toxoplasma titers performed on the thoracic fluid of aborted lambs. This approach has provided a quick, economical, and reproducible means of confirming toxoplasmosis abortion. Small amounts of pooled thoracic fluid can usually be aspirated from the thoracic cavity of lambs during necropsy. If mummified fetuses do not have 1 to 2 mL of fluid, then collection from less mummified littermates may be necessary. The presence of positive toxoplasmosis titers in the thoracic fluid of the fetus confirms toxoplasma abortions. In a farm situation, treatment of toxoplasmosis has proved unrewarding, because infection has usually occurred by the time clinical abortions are observed. This is often difficult to explain to the producer who wants a quick solution to the problem. Producers and their veterinarians are generally left riding out the abortion storm. At this time, our knowledge of toxoplasmosis prevention is also rather scant. Several recommendations may help prevent exposure to toxoplasmosis: (1) reducing the shedding of toxoplasma organisms from kittens and stressed adults by maintaining a constant adult population of healthy neutered cats; (2) planned infection of nonsusceptible ewes or other species with the top layer of mow-stored hay; and (3) feeding of ionophores such as lasalocid or monensin throughout pregnancy. Although the feeding of ionophores for the purpose of preventing toxoplasma abortions in ewes is experimental, recent research suggests that the veterinary profession might wish to consider this practice. A common late gestational management practice aimed at reducing the shedding of coccidia into the lambing barn environment involves the feeding of salt or feed mixes containing ionophores. Several companies currently market sheep salt/mineral mixes containing lasalocid. Other, nonapproved ionophores are commonly in use in the sheep industry. Expanding lasalocid feeding into early and late gestation may provide the possibility of coccidiosis control, improved feed efficiency leading to heavier birth weight lambs, and toxoplasmosis prevention. 3 Prevention of Perinatal Losses Due to Stillbirth and Dystocia Much like abortion rates, the stillbirth and dystocia rates for most flocks remain relatively constant from year to year. Lamb losses due to stillbirth and dystocia generally average about three lamb deaths for every 100 births and account for about 20% of preweaning lamb loss.19 Diagnosis of losses due to simple stillbirth has been previously covered. See Table 1 and the section on post mortem examination of the neonatal lamb. The post mortem examination of a stillborn lamb resulting from dystocia is very similar to that of a ~imple stillborn lamb, except for subtle evidence of trauma. External evidence of a difficult delivery usually includes swollen head, limbs, or tail, or fractured long bones. Post mortem examination often reveals fractured ribs and/or unclotted hemorrhage in the thoracic cavity, or unclotted hemorrhage in the abdomen resulting from a ruptured liver. In the authors' experience, farms that encounter relatively high stillbirth and/or dystocia losses generally encounter problems in the areas of (1) overfeeding, (2) reduced lambing supervision, (3) fetal size incompatibility due to reduced fetal numbers or ram selection, (4) skeletal deformities, (5) abortion diseases, or (6) combinations of the preceding problems. Overfeeding problems usually result from excessive energy intake during


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early and late gestation. These overfeeding problems can often be linked to the free-choice feeding of highly palatable, high-energy feeds. Early gestational self-feeding of small grain haylages, small grain hays, and corn silage often exceeds energy requirements by 150% to 250%. These overfeeding conditions generally lead to excessive fetal size, obese ewes, and subsequent dystocia and stillbirth problems. Ration evaluation and routine condition scoring during early pregnancy can help avoid this situation. Often, producers are not aware of the excessive condition of their ewes until prelambing shearing takes place. Reducing ewe condition during late gestation compounds stillbirth problems by contributing to ketosis and pregnancy disease in the obese ewe. The authors have also observed producers who have unknowingly spawned similar situations by switching ewes from a free-choice system of feeding large round bales or silage to the more regulated and labor-intensive restricted feeding of the lambing barn. Ewe deaths and lamb losses often followed. Farms that classically experience reduced lamb drop numbers often compound the overfeeding problem. Feeding the ewe Hock for a 185% to 225% lamb drop that genetically will produce only a 125% to 140% crop creates similar but less spectacular problems. Fetal size is increased, and ewe condition becomes excessive. If producer assistance with dystocias is not timely, stillbirths and stressed newborn lambs often result. Again, tailoring forage analysis to a particular Hock situation prevents mortality problems while often reducing production costs. Practitioners should also encourage producers to increase lambing performance through proper genetic selection and feeding practices. Breeding ewe lambs is a common practice for many commercial producers. Mortality from stillbirth and dystocia in ewe lambs is often increased by the use of large terminal sire ram breeds on this group of individuals. Selecting ram breeds that encourage lambing ease, and balancing rations to allow growth without overconditioning will help prevent losses. Congenital deformities rarely contribute to major perinatal losses. Congenital defects are generally sporadic and include such items as fetal monsters, hypospadias, cardiac defects, and malocclusions. Except for hereditary chondrodysplasia (spider lamb syndrome) and the arthrogryposis hydranencephaly syndrome, congenital defects seldom have Hock implications. 18,2o

SUMMARY Perinatal mortality is affected by a variety of management factors and disease processes that create significant losses for the sheep industry. Annual production losses prior to weaning include roughly 15% to 20% of the lamb crop. The majority of these perinatal losses occur during the prenatal, natal, and early postnatal periods, with the predominant wave of mortality occurring during the first several days following birth. Causes of perinatal mortality may vary between Hocks and between geographic areas; however, four dominant categories of lamb loss consistently surface: (1) abortions; (2) hypothermia, starvation, and exposure; (3) pneumonia; and (4) stillbirth and dystocia. They account for roughly 50% to 75% of all documented perinatal losses. Veterinarians and producers need to work together to document the type of losses that occur in a given Hock and then design economic prevention programs that address these problems. In most cases, traditional prevention programs will need to be replaced by a comprehensive management scheme addressing nutrition, genetics, housing, marketing, lambing husbandry, and labor.

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REFERENCES 1. Alexander G: Lamb survival: Physiological considerations. Aust Soc Anim Prod 5:113-122, 1964 2. Alexander G: Temperature regulation in the newborn lamb. Aust J Agric Res 12:1152-1174,1961 3. Buxton D, Blewett DA, Trees AJ, et al: Further studies in the use ofmonensin in the control of experimental ovine toxoplasmosis. J Comp Pathol 98:225-236, 1988 4. Dennis SM: Perinatal lamb mortality in western Australia. Aust Vet J 50:443-449, 1974 5. Dennis SM: Perinatal lamb mortality in western Australia. 2. Noninfectious conditions. Aust Vet J 50:450-453, 1974 6. Dennis SM: Perinatal lamb mortality. Cornell Vet 62:253-263, 1972 7. Eales FA: Detection and treatment of hypothermia in newborn lambs. In Pract, 4:20-22, 1982 8. Gates NL: Observations on lamb mortality at the U.S. Sheep Experiment Station. West Vet 15:5-7, 1977 9. Houston DC, Maddox JG: Causes of mortality among young Scottish blackface lambs. Vet Rec 95:575, 1974 10. Huffman EM, Kirk JM, Pappaioanou M: Factors associated with neonatal lamb mortality. Theriogenology 24: 163 -168, 1985 11. Johnston WS, Maclachlan GK, Murray IS: A survey of sheep losses and their causes on commercial farms in the north of Scotland. Vet Rec 106:238-240, 1980 12. Kirk JH: Reducing lamb mortality: A two-year study. Vet Med SAC August 1982, pp 1247-1249 13. Linklater KA: Abortion in sheep. In Pract 1:30-33, 1979 14. McKenzie RL, Grant JL: A survey of lamb mortality in a commercial Hock of sheep. Rhod Vet J 6:69-72, 1976 15. Meaker HJ, van Niekerk CH: Birth mass and neonatal mortality of lambs as affected by level of nutrition of the ewe. S Afr J Anim Sci 4:25-26, 1977 16. Purvis GM, Ostler DC, Starr J, et al: Lamb mortality in a commercial lowland sheep Hock with reference to the inHuence of climate and economics. Vet Rec 104:241242, 1979 17. Rook IS: Why didn't it live? Shepherd 34:26-27, 1989 18. Rook JS, Yamini B, Steficek B: AGH syndrome: Cooperation answers questions. National Wool Grower, 78(3}:24-25, 1988 19. Rook}, Bartlett P, Trapp A, et al: Lamb mortality-a reHection of Hock health. In Proceedings, 65th Annual Postgraduate Conference, Michigan State University, College of Veterinary Medicine, East Lansing, January 25, 1988, pp ml-ml0 20. Rook J: The spider lamb syndrome: A 2-year perspective. Sheep 7(7}:19-22, 1986 21. Slee }: The effects of breed, birthcoat, and body weight on the cold resistance of newborn lambs. Vet Rec 27:43-49, 1978 22. Slee J: Cold stress and perinatal mortality in lambs. Vet Annu 16:66-69, 1976 23. Stafford JW, Hoversland AS: A study of lamb mortality in a western range Hock. Anim Sci 19:265-273, 1960 24. Sykes AR: InHuence of breed, birth weight, and weather on the body temperature of newborn lambs. Anim Prod 22:395-402, 1976 25. Tigner JR, Larson GE: Sheep losses on selected ranches in southern Wyoming. } Range Manage 30:244-252,1977 26. Whitelaw A: Survey of perinatal losses associated with intensive hill sheep farming. Vet Annu 16:60-65, 1976 27. Wise JK: Animal health expenditure by livestock producers. J Am Vet Med Assoc 192:236-238, 1988

Address reprint requests to Joseph S. Rook, DVM College of Veterinary Medicine Michigan State University East Lansing, MI 48824

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