Minimizing lamb losses (Proceedings)

In a 1996 survey of over 5,100 U.S. sheep producers, 9.4% of lambs born alive were reported to have died prior to weaning.1 Worldwide, hypothermia and starvation are considered to account for the majority of preweaning lamb losses, with predation and respiratory disease also being important causes.2 Management factors strongly influence these problems, and a few minor adjustments in lambing procedures may reap significant economic benefits for the motivated producer. In this seminar, common management practices that contribute to lamb mortality will be described, and a variety of corrective measures will be presented to aid the veterinarian in reducing lamb mortality. Interested readers are encouraged to access the outstanding and very comprehensive review of newborn lamb mortality by Rook and colleagues.2

Ensuring intake of colostrum

Adequate intake and absorption of immunoglobulin from colostrum is a pivotal event in lamb survival, and producers need to be reminded of its importance prior to each lambing season. An easy-to-remember postpartum lamb care rule is "clip, dip, and strip": 1) Clip the umbilicus to a length of approximately 3 cm to limit its contact with the ground; 2) Dip the umbilicus in an appropriate antiseptic; and 3) strip a small stream of milk from each teat of the ewe. The latter process removes the keratin plug, which can be too tenacious for the newborn lamb to remove. It also enables prompt recognition of agalactia or mastitis.

An extra supply of colostrum is frequently needed for lambs born to ewes with bacterial mastitis and mastitis caused by clinical ovine progressive pneumonia (OPP) infection, as well as for orphaned lambs and triplets. In flocks with aggressive OPP control measures in place, colostrum from OPP-negative ewes is in particularly high demand. Mature ewes with adequate colostrum to feed a single lamb can be hand-milked once their newborn has fed. Ewes with stillborn lambs represent another source. Oxytocin (10 IU IM) should be administered to maximize milk letdown during hand milking. Multiple milkings of such ewes over the course of the first day postpartum can generate an ample supply of extra colostrum. Extra colostrum can be frozen in an ice tray, and each cube of colostrum can be quickly thawed in a sealed plastic bag immersed in hot water. One standard ice cube typically has approximately 1 ounce (30 ml) of volume; each lamb that requires hand-fed colostrum should be fed 45-60 ml / kg bodyweight as soon as possible after birth.2 Red rubber catheters can serve as effective stomach tubes to make the process time-efficient. Caprine or bovine colostrum can be used if ovine colostrum is not available. Feeding lambs colostrum from does infected with caprine arthritis-encephalitis (CAE) virus may result in persistent seropositivity to the OPP virus, owing to the cross-reactivity in many assays of antibodies specific for CAE with those specific for OPP.3 In addition, such lambs are at risk for clinical "cross infection" with the CAE virus, the most common clinical manifestation of which is synovitis.3

Producers frequently forget that dystocia can limit the dam's ability to stand, and any pain resulting from dystocia may limit mothering ability. In addition, dystocia can greatly limit the neonate's ability to effectively nurse, particularly if the tongue is swollen. In dairy calves, dystocia has been associated with stillbirths and an increased risk of death within the first 30 days of life.4 Ewes experiencing dystocia should be hand-milked after oxytocin administration, and the lambs should be tube fed colostrum because it is very likely that the ewe may remain recumbent and uninterested in mothering until the pain and stress subside. To that end, administration of analgesics (flunixin meglumine 1.1-2.2 mg/kg IV or SC) should be strongly considered in postpartum care of dystocia cases, in order to facilitate the ewe-lamb bond and facilitate subsequent nursing. Dams experiencing severe dystocia may require opiate analgesics, such as butorphanol (0.1 mg/kg IV, IM, or SC q 4-6 h), as well as supplemental oxytocin and hand-milking / hand feeding for the first 1-2 days postpartum. Another option for pain management in such cases is lumbosacral epidural administration of morphine (0.1 mg / kg of 15 mg/ml solution, diluted with 0.9% sodium chloride to a volume of 0.2 ml/kg); alternatively, preservative-free morphine can be administered as a lumbosacral epidural (0.1 mg/kg).5,6 Given the subjectively high impact that puerperal metritis carries to the postpartum ewe, the author recommends that antimicrobial therapy be considered for ewes that require extensive intrauterine manipulations for correction of dystocia.

Limiting starvation losses

In addition to ensuring colostrum intake by newborns, successful grafting techniques can greatly limit lamb losses from starvation. The most commonly employed method is the forced graft, wherein the dam is restrained by halter to a post in a small pen or lambing jug, and the lamb to be grafted is turned in and allowed to nurse. Acceptance by the ewe typically occurs within 24-72 hours.

If the recipient ewe has just finished lambing, her placenta can be rubbed or tied onto the orphaned lambs(s). The scent of the placenta and uterine fluids is the means by which the bond is established; ewes in the immediate postpartum period are generally the most amenable to grafting. The ewe and lamb(s) should be kept in a small pen for close observation for 2-3 days. If the recipient ewe has given birth to a stillborn lamb, or if the lamb dies in the neonatal period, the lamb can be skinned and the skin tied around the lamb to be grafted.

If the recipient ewe is lactating with a single lamb of her own, the orphan must be covered in the scent of the recipient dam's young. This can be achieved by placing a clean length of orthopedic stockinette over the trunk of the dam's own lamb. Cut holes for the arms and legs; include a hole for the prepuce if the lamb is a male. Leave this on for 24 hours. At that time, take it off of the ewe's own lamb, turn it inside-out, and place it on the lamb to be grafted. Anecdotally, the success of this procedure may be increased (at the time of introduction of the lamb to be grafted) by restraining the ewe and placing a gloved hand in the vulva to induce straining (as would occur during parturition). Any lochia retrieved from the vagina can be placed onto the coat of the lamb to be grafted. One then tapes the front legs together of both the ewe's own lamb and the orphan lamb, so they struggle to stand for a while, thereby exhibiting behavior similar to newborn lambs struggling to stand. The tape can be removed after approximately 15 minutes. The ewe and her new lambs should be monitored in a small pen or jug for 2-3 days.

If attempts to graft lambs fail, orphaned or rejected lambs can be fed lamb milk replacer from a milk bar. The target intake for milk replacer is 15-20% of bodyweight per lamb per day, divided into as many feedings as possible (at least 3) to limit the likelihood of bloat.

In the author's experience, illness in the dam can be detected for roughly one in four of lambs with clinical or necropsy evidence of starvation. Therefore, a full physical examination of the dam of an ill or poor-doing neonate is warranted, as subnormal milk production and lack of normal mothering ability may occur with illness in the dam. The author recommends that the 5 M's be considered as common differential diagnoses in ill, postpartum ewes:

     • Mastitis: Bacterial or retroviral (OPP)

     • Metritis: One can use a vaginal speculum or abdominal pressure with the ewe or doe tipped up on its rump to find evidence of fetid vaginal discharge; palpate the abdomen carefully or perform ultrasonographic examination to detect a retained fetus

     • Metabolic disease: Pregnancy toxemia / hypoglycemia, hypocalcemia

     • Musculoskeletal disease: Lameness from footrot and retroviral arthritis are common examples

     • Mannheimia, (Pasteurella) multocida, Mycoplama: Pneumonia. Pulmonary auscultation can be facilitated by use of a rebreathing bag. Asymmetry of sounds from one side to the other may be the sole abnormality noted. Fever can be inconsistent in chronic cases, but affected ewes are often thin.

Although relatively uncommon in range ewes in the author's home region, significant internal parasite burdens in the dam should also be considered as a cause of ill thrift in lambs.

Treatment of hypothermia

Warming boxes can aid chilled newborn lambs in establishing normal thermoregulatory capacity. Towel-drying is recommended in advance, to limit further heat losses from evaporation of moisture from the skin.2 A simple model consists of a towel-lined milk crate with a hair drier or heat lamp propped or suspended above the box to direct heat into the crate's center. The air intake screens on hair dryers must be routinely cleaned to prevent occlusion by barn dust. Immersion of the lamb in warm water is not recommended, as this may remove enough of its scent to trigger rejection by the ewe. Intraperitoneal injection of 5 ml of a 20% dextrose solution has been advocated to treat hypoglycemia associated with hypothermia, however, it carries the risk of damage to viscera by an untrained caretaker, and disinfection of the site and prophylactic antimicrobial therapy have been recommended.2 Subcutaneous administration of warmed 5% dextrose (30 ml) is an alternate method.

To facilitate thermoregulation in smaller, weaker lambs, clean wool socks can be cut to fit over the forelegs, thorax, and abdomen. The weak lamb (and its siblings) should be removed from the ewe. The sock should be placed over the lamb, left on for 20-30 minutes, turned inside-out, and reapplied to make the lamb's scent available to the ewe. Siblings should be coated as well. The lamb(s) can then be reunited with the dam.

Maintaining pen hygiene

Many sheep producers utilize lambing jugs, or pens, as a means of ensuring that the ewe bonds well with her lambs and that the lambs have ample opportunity to nurse in the immediate postpartum period. Using lambing jugs as maternity pens in which parturition occurs is commonly practiced; however, the accumulation of organic debris and uterine fluids can contribute to a hygiene problem. A windbreak, such as an outer barn wall or a line of large straw bales, with a few panels or bales as sidewalls, often makes for a more hygienic set of lambing jugs than a crowded barn or shed. Rotation of lambing jugs from established indoor facilities to temporary outdoor facilities may be necessary to enable cleaning and drying of soiled pens under conditions of heavy use. Ultrasonographic staging of pregnancy or breeding of groups of ewes at 3-4 week time intervals can aid in limiting the occupancy of lambing areas to only those ewes likely to lamb over defined periods during the subsequent spring.

During periods of rain or snow, fully-fleeced ewes may transport significant amounts of moisture into lambing barns, resulting in pathogen accumulation and a reduction in air quality. In addition, heavy fleece surrounding the udder may result in the accumulation of fecal matter and uterine fluids in close proximity to the udder, thereby increasing the risk of enteric disease in the lambs. Crutching (shearing perineal and inguinal wool) or full shearing of ewes may be a helpful practice to limit these problems. Shorn ewes will require increased dietary energy to meet the increased needs for thermoregulation. Shorn ewes tend to lamb in sheltered areas, which may carry the additional benefit of reducing the risk of neonatal hypothermia.

In jugs and small pens, water buckets should be raised off of the ground to limit spillage and prevent lamb drowning deaths – some ewes will lamb directly into the bucket if it is maintained on the floor. If water troughs are used, bricks should be placed inside them to enable lambs that fall in to crawl out. Water troughs should be located at the lowest point of the floor or outdoor slope to maintain a dry pen.

Ensuring adequate ewe nutrition

For ewes in late gestation and lactation, provision of grass hay and a grain source is likely to result in insufficient intake of protein and vitamin E; depending on the forage source and the amount of grain fed, the ration can also be limited in selenium and energy content. Vitamin E supplementation may be warranted for ewes fed stored forages and silage, at least until green pasture is available for grazing. Selenium supplementation needs vary greatly by the geographic region in which the forages are grown. Producers who follow standardized rations in sheep lay journals are likely to meet the protein and energy content of ewe rations, provided that high-quality, higher-protein forages (e.g. alfalfa hay) are fed during the last trimester of gestation and into lactation.2 However, variation in forage quality is often not taken into account when such standardized rations are fed, leading to potential deficiencies of protein and energy. Rook and colleagues2 have estimated that poor-quality hay, haylage, or silage, fed alone or in combination, provide only 50-75% of crude protein needs for lactating ewes. Protein deficiency, in particular, may limit milk production by ewes and contribute to starvation losses, particularly for ewes nursing multiple lambs. Starvation losses in lambs at 1-3 weeks of age, or losses caused by combinations of starvation and pneumonia in this age group, warrant careful exploration for protein or protein-energy malnutrition of the ewe flock.2 Supplemental crude protein can be provided by urea feeding in licks or tanks, nitrogen supplementation of silage or grain, or provision of legume hay or oilseed meal. If hay is the preferred means of providing crude protein, hay fed for lactating ewes should contain at least 16% crude protein.2

When evaluating the economics of protein supplementation, owners frequently balk at the expense. It is critical, however, that the context of protein supplement purchasing be viewed in a rational manner. The price of such supplements should not be evaluated on the price per pound of the supplement, but the price per pound of crude protein that the supplement contains.7 For example, alfalfa hay containing 20% crude protein may cost $180 per ton in many locales during certain times of the year. This equates to 400 pounds of crude protein at a cost of $180, or roughly 45 cents per pound of crude protein. Compare this to soybean meal (44% crude protein) at $380 per ton, which provides 880 pounds of crude protein at $380, or roughly 43 cents per pound of crude protein. In this example, soybean meal might be a more economical means of providing crude protein, if transport, storage, and labor costs are considered equal. For smaller holdings, the more compact soybean meal may offer advantages over alfalfa hay in terms of available storage space.

Summary

Ensuring lamb survival requires several simple steps to ensure colostrum ingestion and ensuring a satisfactory ewe-lamb bond. Appropriate attention to pain management for ewes that experience dystocia can contribute to these two goals. For shed lambing operations, attention must be paid to pen hygiene, and when lambing rates are high, use of ancillary shelters other than the established lambing pens may be necessary to limit complications from heavy environmental contamination. Appropriate levels of protein in late gestation and early lactation are also vital to lamb survival as these nutritional factors can greatly impact milk supply.

References

1. Anonymous. Reference of 1996 U.S. Sheep Health and Management Practices. National Animal Health Monitoring System, Animal and Plant Health Inspection Service, United States Department of Agriculture, 1996, p. 6.

2. Rook JS, Scholman G, Wing-Proctor S, et al. Diagnosis and control of neonatal losses in sheep. Vet Clin N Amer: Food An Pract 6: 531-562, 1990.

3. Rowe JD, East NE. Risk factors for transmission and methods for control of caprine arthritis-encephalitis virus infection. Vet Clin N Amer: Food An Pract 13:35-53, 1997.

4. Lombard JE, Garry FB, Tomlinson SM, et al. Impact of dystocia on health and survival of dairy calves. J Dairy Sci 90:1751-60, 2007.

5. Hendrickson DA, Kruse-Elliott KT, Broadstone RV. A comparison of epidural saline, morphine, and bupivicaine for pain relief after abdominal surgery in goats. Vet Surg 25:83-87, 1996.

6. Pablo LS. Epidural morphine in goats after hind limb orthopedic surgery. Vet Surg 22: 307-310, 1993.

7. Fisher, MJ, Colorado State University Extension. Personal communication, 2008.