An Examination of the Selenium Nutrition of Sheep in Victoria

Abstract

The selenium nutrition of sheep throughout Victoria was assessed by a survey of the blood glutathione peroxidase activity in 708 flocks. It was shown that the blood glutathione peroxidase activity in sheep had a seasonal variation with lowest levels in the spring. The enzyme activity was correlated with the blood selenium concentration. Areas where blood selenium was less than 0.03 micrograms/ml in spring were defined. Sheep with low selenium nutrition were grazing pastures in the high rainfall areas on acid soils, particularly those derived from granite. Selenium concentrations in pasture samples examined were greater than 0.02 mg/kg, and it was found that superphosphate application had no significant effect on the selenium content of pasture. However, management practices such as high stocking rates and rates of application of superphosphate to pasture were associated with low blood glutathione peroxidase activities in sheep. It was concluded that the selenium nutrition of most of the sheep flocks in Victoria is adequate, and that the deficient areas are localised. There seems little requirement for supplementation of adult sheep. As the delayed type of white muscle disease in spring lambs appears to be the main selenium-responsive disorder, direct supplementation of lambs in the low selenium areas would be the most effective method of ensuring adequate selenium nutrition.

Cyanogenesis potential and iodine concentration in white clover (Trifolium repensL.) cultivars

“…Direct effects of cyanide on Se metabolism have been recorded in sheep (Rudert & Lewis 1978;Gutzwiller 1993), rats (Beilstein & Whanger 1984), and chicks (Elzubeir & Davis 1988). The seasonal occurrence of symptoms of Se deficiency in stock has been associated with periods of active clover growth (Underwood 1966;McDonald & Caple 1977;Caple et al 1980). It is not known if this association is solely the result of the low Se content of clover herbage, which is lower than browntop, cocksfoot, or ryegrass (Davies & Watkinson 1966), or if the cyanide released by clover markedly reduced absorption and utilisation of ingested Se.…”

Increasing Selenium Concentration in Milk: Effects of Amount of Selenium from Yeast and Cereal Grain Supplements

“…It is principally when Se supplements are fed to Se-deficient cows that production responses can be expected. Witchel et al (1994) suggested cows grazing pasture with less than 30 g of Se/kg of DM would have inadequate Se intakes, whereas Caple et al (1980) considered that pasture with 50 g of Se/kg of DM would provide adequate Se. The Se concentrations in our pastures and supplements were always greater than 60 g of Se/kg of DM, indicating sufficiency of Se in the basal diet.…”

“…Binnerts (1979) reported milk Se concentrations of 3 to 5 g of Se/kg of milk from cattle in low-Se areas in the Netherlands and 6 to 11 g/kg for those from high-Se areas. Variations in Se concentrations in pastures (10 to >50 g of Se/kg of DM; Caple et al, 1980) may lead to variations in concentrations in milk, but the effects are likely to be relatively small unless significant amounts of Se are added in fertilizer (Aro et al, 1998). The Se concentrations in concentrate supplements, such as wheat (1 to 117 g/ kg of DM) and lupins (10 to 488 g/kg of DM), vary to a greater degree than those in pasture (White et al, 1981) and are therefore more likely to affect concentrations in milk.…”

Effect of dietary selenium on erythrocyte glutathione peroxidase and blood selenium in two types of Finnsheep genetically selected for high and low glutathione peroxidase activity

“…The decrease of average GSH-Px activity within the experimental period cannot be explained by an analytical failure as the levels were rechecked later from freezed samples. A seasonal variation in blood GSH-Px activity in sheep has been reported (CAPLE et al, 1980). Thc seasonal variation in the present study could partly arise from changcs in oxidative processes contributed by vitamin E. However, the effect of vitamin E on GSH-Px activity has been reported to vary between species and in lambs it has been shown to have no effect on this selenoenzyme (GODWIN et al, 1975).…”