Vitamin E and selenium status of sheep during autumn in Western Australia and its relationship to the incidence of apparent white muscle disease

Abstract

This paper reports on the status of vitamin E and selenium in weaner and adult sheep in Western Australia (WA) during autumn, and its relationship to the incidence of apparent white muscle disease (WMD). A survey was conducted in which blood samples were taken from 10 weaner sheep (8–12 months of age) and 10 adult ewes (3 years of age) from flocks on 38 properties within the main southern agricultural region of WA, an area carrying ~10 million sheep. Deficiency of vitamin E was defined as a plasma α-tocopherol concentration less than 0.7 mg/L. Selenium deficiency was defined as whole blood glutathione peroxidase (GPx) activity less than 50 U/L. Incidence and severity of apparent WMD were defined in terms of elevated plasma activities of creatine kinase (CK) or aspartate aminotransaminase (AST). Of the weaner flocks, 58% (22/38) had mean plasma vitamin E concentrations in the deficient range (<0.7 mg/L) and 50% (19/38) had mean CK activities above 400 U/L (mild WMD); four of these flocks had mean CK activities over 1200 U/L (severe WMD). Of all the individual weaner sheep sampled, 6% had plasma CK activities >1200 U/L. It is likely that the incidence of vitamin E deficiency would have been higher had it not been for unseasonal summer rain germinating pasture on eight of the survey farms in the northern wheat belt. Flocks from farms with an evident green flush to their pastures had higher vitamin E levels than flocks grazing dry pasture. Vitamin E deficiency was less common in adult sheep than weaner sheep, with only 16% of flocks (6/38) having mean plasma concentrations below 0.7 mg/L and 11% (4/38) with CK values above 400 U/L. Selenium deficiency was less common than vitamin E deficiency and was mostly confined to adult flocks, with only 5% (2/38) of these having mean GPx values below the critical value of 50 U/g haemoglobin. For both weaner and adult sheep classed as vitamin E deficient, CK and AST activity in plasma was best described by a combination of plasma vitamin E concentration and whole blood activity of GPx (significant linear step wise regression, P < 0.001). The present study shows that subclinical vitamin E deficiency (<0.7 mg/L) was widespread in weaner flocks in WA during autumn and that, based on the biochemical data, deficiency was associated with apparent severe muscle damage in 6% of weaner sheep sampled. Recommended strategies to treat weaner sheep showing signs of WMD include dosing with 2000–4000 mg vitamin E either by injection, oral drench or by spraying it onto supplementary grain. The level and frequency of dosing depends upon the severity of the WMD symptoms. Less is known about preventative treatment, but recent evidence suggests that providing weaner sheep with access to saltbush during autumn may prove to be a practically useful strategy. Selenium supplements should also be supplied to weaner and adult sheep in areas known to be selenium deficient.

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The role of oxidative stress in small ruminants' health and production

“…Selenium is an essential element in the diet of animals and is important in host antioxidant defense and immune function (Rivera et al, 2003;Smith et al, 2005). A deficiency can result in ill thriftiness, reproductive losses, reduced reproductive efficiency, wool yields and reduced growth rate in young lambs throughout the growing period (Whelan et al, 1994;Rivera et al, 2003;Robson & Plant, 2007) and a severe selenium deficiency can lead to sudden death from white muscle disease (White & Rewell, 2007). Selenium is a component of the selenoenzyme glutathione peroxidase (GSH-Px), which acts as an antioxidant and helps prevent tissue damage caused by free radicals.…”

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