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Vitamin E & Selenium Concentration in Ewes and Lambs
Vitamin E and Selenium Concentrations in Ewes and Their Lambs: Research Results From One Michigan Flock
Drs. J. S. Rook, M. Kopcha and B. Bartlett
Introduction
Traditionally, Michigan sheep producers have supplemented newborn lambs with selenium and vitamin E preparations to prevent "white muscle disease" and other selenium/tocopherol deficiency-associated neonatal losses. Supplementation customarily involves injectable vitamin E/selenium preparations and/or oral nutritional supplement products ("pig pump" preparations) containing vitamin E and selenium. Administration of injectable or oral products to each newborn lamb occurs shortly after birth, and involves expense for both product and labor. Currently, the routine administration of vitamin E and selenium preparations to newborn lambs is a recommended management practice. However, why should producers need to supplement newborn lambs at all, if the ewe diet contains adequate concentrations of both nutrients? Perhaps this question might best be answered by reviewing what we already know about relationships between vitamin E, selenium, the ewe, her lamb, and Michigan production systems.
What We Know About Vitamin E
Serum samples suggest that ewes grazing lush green pasture display very high concentrations of vitamin E in their serum. This is in direct contrast to the low serum vitamin E status of ewes fed dry stored feeds or housed in confinement facilities. Furthermore, low fetal liver vitamin E concentrations suggest that it is normal for lambs to be born with a vitamin E deficient status. Thus, in a non-supplemented setting, the vitamin E deficient newborn's principal source of vitamin E is colostrum from the dam. It would appear that "Mother Nature" has designed a reasonable system for transfer of vitamin E to the lamb, if the ewe lambs on lush green vitamin E-rich pasture and man does not interfere. However, most Michigan production systems utilize winter or spring lambing systems that are months removed from lush green fall pasture. After long stressful winter months of a diet of dry, stored feeds (low in vitamin E) parturition approaches with depleted vitamin E reserves in the dam. Vitamin E that is available for colostral transfer to the lamb is minimal; thus the rationale for oral or injectable supplementation.
What We Know About Selenium
Producers and their veterinarians involved in sheep production recognize that soils, forages, and grains in the Great Lakes Region are deficient in selenium. Serum selenium levels mirror this low concentration of selenium observed in sheep feeds. Producers address selenium deficiency by supplying ewes and lambs with selenium- supplemented (90 ppm Se current legal limit) trace-mineral salt. However, while the upper limit for selenium (90 ppm) in sheep trace mineral salt is set by law, selenium levels in commercial sheep salt and mineral products can be quite variable (less than this maximum 90 ppm). We also know that in most farm animal species selenium is transferred from the dam to her offspring in utero, with a slight tendency for concentration in the fetus. Selenium, unlike vitamin E, is not readily transferred in the milk. Therefore, serum selenium concentrations in the newborn lamb should reflect serum selenium concentrations in the ewe at the time of birth. Therefore, an adequate serum selenium concentration in the ewe should indicate an adequate serum selenium concentration in her newborn lamb(s). If the above assumptions are valid, random sampling of the ewe flock just prior to lambing might be a useful indicator of the non-supplemented selenium status of the neonate. However, there is little available information regarding ewe/lamb selenium status and vitamin E relationships. Could we avoid the labor and expense involved with individual supplementation of newborn lambs by adding selenium and vitamin E to the diet of the ewe? What dietary levels might be appropriate?
If you owned 10 ewes, injecting newborn lambs with vitamin E and selenium preparations or orally administering vitamin E preparations might not seem like much of a problem. However, producers who lamb 500 to 1,000 ewes in a drop-lot system might feel otherwise. Increases in flock numbers place enormous seasonal demands on both labor and capital. Efficient alternative methods for providing vitamin E and selenium to newborn lambs are needed. Providing these nutrients, within the constraints of a large commercial production system, requires assessment of the relationship between vitamin E and selenium levels in both the ewe and her newborn lamb(s).
Selenium and Vitamin E Research
During the 1995 lambing season 50 ewes (50/400 ewes or 12.5% of a commercial flock) and their 83 lambs were sampled for serum selenium and vitamin E concentrations. The flock had been wintered on dry hay and switched to a ration of free-choice high-quality orchard grass balage and 1 lb of shelled corn just prior to lambing. Lambing occurred in early May in facilities typical of Michigan drop-lot systems. The flock was located in the Upper Peninsula of Michigan and all sampling occurred prior to the onset of grazing season.
In an effort to mimic normal commercial production practices, selenium supplementation involved only free-choice access to commercially available selenized sheep trace mineral salt containing 90 ppm selenium. Vitamin E concentrate was also added to the trace mineral salt (2.5 lbs. of 20,000 IUs/lb. vitamin E concentration per each 50 lb bag of selenized trace mineral salt). Thus, per ewe consumption (based on 1/2 oz of trace mineral salt/head/day) supplied 1.28 mg selenium and 31.25 IU of vitamin E per day. Ewes were sampled for serum selenium and vitamin E concentrations at the time of lambing. Their lambs were similarly sampled 48 hours after birth. The 48-hour delay allowed lambs adequate time to absorb colostrum rich in vitamin E. The lambs received no additional selenium or vitamin E supplementation at birth.
Do Ewe Serum Selenium and Vitamin E Concentrations Adequately Reflect the Serum Vitamin E and Selenium Status of the Newborn Lamb?
The following graphs represent the serum selenium and vitamin E data resulting from sampling 50 ewes and their 83 lambs. The data are presented as mean serum selenium and vitamin E concentrations. Normal value ranges are as reported by the Animal Health Diagnostic Laboratory for adult ewes and lambs.
At the time of parturition, the mean sera vitamin E and selenium concentrations of the dams appeared to be reasonable indicators of similar values in the lamb(s). While mean sera concentrations reported for the dams and their offspring are not numerically identical, the correlation of the mean sera concentrations to the laboratory reported "normal ranges" for specific age groups was predictable. In this particular group of animals, adult "normal range" mean sera vitamin E concentrations in the dams appeared to produce lambs that exhibited at least "normal range" to elevated vitamin E concentrations. Similarly, marginally adequate selenium levels in the ewe flock resulted in marginally adequate selenium levels in their lambs, even with daily supplementation of selenium in the free-choice trace mineral salt (at the maximum legal 90 ppm limit) .
What Have We Learned?
While sample numbers are not large (50 ewes and their 83 lambs), the results appear to support serum vitamin E and selenium concentrations of the parturient ewe as an indicator of the potential vitamin E and selenium status in the post-suckle newborn lamb. It appears that (in this particular flock) the legal selenium levels allowable in trace mineral salt were marginally adequate for the ewe and her newborn lamb. However, a very acceptable 5.5% periparturient lamb mortality rate suggests that, at least in this particular flock, the reported marginal selenium levels may not warrant further additions (above the 90 ppm level in the trace mineral salt) of selenium to the ewes or lambs.
In this particular flock, vitamin E concentrations measured in both ewes and lambs appeared to be adequately addressed by the feeding program and additions of vitamin E to the salt mix. However, vitamin E supplementation may not be as straightforward as simple additions of vitamin E concentrate to the salt mix. Unlike most Michigan flocks, this producer fed very high quality balage during late pregnancy. High-quality haylage that is stored properly can contain high levels of vitamin E. Vitamin E analysis of balage reported 74.1 IU of vitamin E/KG of dry weight. This value is about half the expected vitamin E concentration of fresh cut alfalfa. The high vitamin E content of the balage may have masked the contribution of the vitamin E addition to the salt mix. This is not entirely a sheep issue--the economic potential for the enormous amounts of vitamin E contained in high-quality haylage might be of interest to dairy producers, who might be able to greatly reduce the costs of adding vitamin E concentrate to dairy rations by incorporating high-quality haylage in the diet. Addressing perinatal mortality issues through the diet of the pregnant ewe would seem to be more sensible than dealing with vitamin E and selenium issues by individually injecting each lamb.