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  • Title: An assessment of the selenium, copper and zinc status of sheep on cultivated pastures in the Natal Midlands.
    Author: Van Ryssen JB, Bradfield GD.
    Journal: J S Afr Vet Assoc; 1992 Dec; 63(4):156-61. PubMed ID: 1491420.
    Abstract:
    Blood samples were collected from sheep on 24 farms in the Natal Midlands to ascertain the selenium, copper and zinc status of sheep kept under intensive grazing conditions on cultivated pastures in this region. The mean erythrocyte glutathione peroxidase activity was 34.1 enzyme units (EU: nmol NADPH oxidised min-1 mg-1 haemoglobin). A total of 59.4% of the samples contained less than 30 EU, a level below which a marginal deficiency may exist. The mean selenium concentration in whole blood was 0.57 mumol l-1. Sixty four per cent of the samples contained less than 0.63 mumol l-1, a level below which the animals were considered to be marginally deficient. The mean copper concentration in plasma was 16.1 mumol l-1 and that of zinc 15.0 mumol l-1. On none of the farms was the copper concentration in plasma below the concentrations accepted to represent a marginal deficiency, and ewes on only one farm had relatively low plasma zinc concentrations. It is concluded that many sheep grazing cultivated pastures in the Natal Midlands may be marginally deficient in selenium. However, the selenium status in sheep should be determined on individual farms before supplementation is recommended, as external sources of selenium are often supplied, mostly unintentionally. Seasonal variations in blood selenium concentrations did not follow a specific trend, probably because the sheep were grazing cultivated pastures for most of the year and feeding practices differed from farm to farm. It is therefore suggested that the selenium status of sheep be determined at the pre-mating and pre-lambing stages rather than in a specific season of the year.
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