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5. Vitamin E

Vitamin E functions as an antioxidant inanimal tissues, and deficiency predisposessheep to muscle damage (myopathy).Selenium and vitamin E have similar rolesin the prevention of muscle damage byoxidants produced during tissuemetabolism, but they have independentsites of action. Selenium treatmenttherefore reduces the likelihood of muscledamage from combined deficiencies ofselenium and vitamin E. Extreme vitamin Edeficiency alone may induce muscledamage in sheep in Victoria, (Hucker 1983),and elsewhere, (Steele et al. 1980), evenwhen selenium status is adequate.

Vitamin E is most abundant in greenpastures. Several forms of vitamin E arepresent in herbage as tocopherols (Hucker1982). The alpha-tocopherol form is themost important with concentrations rangingfrom 30 to 60 mg alpha-tocopherol/ kg wetweight.

5.1 Occurrence of vitamin Edeficiency in Victoria

In Victoria, vitamin E deficiency occursmainly in sheep less than 18 months of agegrazing on oat stubble or grass pasturesthat have been dry for several months andcontain no green vegetation (Hucker 1983).The disease has also been observed inadult sheep on some properties. Sheephave been affected in north-easternVictoria, Gippsland and the WesternDistrict, particularly during extended dryperiods in autumn when grain supplementswere fed. Widespread cases occurredduring the summer and autumn of the 1982-83 drought.

Vitamin E deficiency has occurred inhoused sheep fed dry feed for extendedperiods (Hucker 1982), and in sheep fed ongrain (Hucker 1983). Housed sheepsupplemented with 50 mg alphatocopherolacetate/day had 5 kg higher body weightsand produced 16% more wool in six monthsthan untreated sheep (Hucker 1983).

5.2 Signs of vitamin E deficiency

Affected lambs show signs of lameness.Commonly the lambs are illthrifty anywaydue to the quality of the available feed. Thenumber affected in flocks ranges from 5 to10%. Usually lambs are found dead, butothers may be reluctant to move, collapsewhen driven or may be unable to stand.They may pass red-brown stained urine.

5.3 Diagnostic methods

Clinically, vitamin E-responsive whitemuscle disease cannot be differentiatedfrom selenium-responsive white muscledisease. To diagnose myopathy from eithercause, blood samples are collected fromlambs in the flock for assay of the enzymecreatine kinase released from damagedmuscles into plasma. Confirmation of thisdiagnosis requires histopathology of muscletissue.

The selenium nutrition is assessed by bloodglutathione peroxidase activity, and vitaminE nutrition is assessed from plasma vitaminE concentration. Plasma vitamin E (alpha-tocopherol) concentrations less than 3umol/l indicate the vitamin E intake of sheepis inadequate.

Plasma vitamin E assays can be arrangedthrough the Regional VeterinaryLaboratories. Special precautions have tobe taken during collection and shipment ofsamples (Sinclair and Slattery 1978) andthe details should be obtained from thelaboratory.

5.4 Treatment

Usually flocks are drenched with selenium(0.1 mg Se/kg liveweight) if they are in amarginal selenium area. Affected flocks inextended dry periods should be given adrench containing 1 to 4 g vitamin E(Hucker 1983, Steele et al. 1981). Thistreatment has provided protection for up tosix weeks.

Vitamin E preparations available fordrenching sheep include Microvit E 50 E.S.(May and Baker) and Robimix E type 50 SD(Roche).

5.5 Prevention

Ensuring that lambs have adequateselenium nutrition is one way of minimisingthe risk of myopathy due to vitamin Edeficiency. A practical way of preventing thedisorder is to provide lambs with a greenpick (even edible green weeds) in summer.Sheep on grain rations alone require 50 mgalphatocopherol acetate/day (Hucker 1983).

References

Hucker, D.A. (1982) Nutritional problems inthe "Sharlea" (housed superfine wool)sheep industry. In "Australian Advancesin Veterinary Science, 1982". (M.G.Cooper, Ed.) Australian VeterinaryAssociation, Artarmon, NSW. p213-215.

Hucker, D.A. (1983) White muscle diseasein sheep in the Western District during

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the drought of 1982/83—Use of vitaminE treatments. In "Trace Element Reviewpapers, 1982". Agricultural ServicesLibrary, Department of Agriculture,Victoria.

Sinclair, A.J. and Slattery, W. (1978) Bloodcollecting tube as a contaminationsource in vitamin E fluorometry. ClinicalChemistry, 24:2073.

Steele, P., Peet, R.L., Skirrow, S.,Hopkinson, W. and Masters, H.G. (1980)Low alphatocopherol levels in liver ofweaner sheep with nutritional myopathy.Australian Veterinary Journal, 56:529-532.

Steele, P., McKenzie, D.P., Skirrow, S.,Peet, R.L. and Doncon, G. (1981)Selenium and tocopherol treatment ofovine weaner nutritional myopathy in"Trace Element Metabolism in Man andAnimals, 4". (J. McC. Howell, J.M.Gawthorne and C.L. White, Eds.) pp.210-213, Australian Academy ofScience, Canberra.