초록
This study determined the concentrations of micro-minerals in pastures, in feed supplements and in grazing, reproducing ewes, at different times during the year, at three farms in Northern China. Samples were collected 5 to 8 times during the year and analysed for selenium, copper, iron, molybdenum and zinc. On two farms selenium concentrations in both pastures and animal tissues were low for part of the year. The lowest concentrations in pasture (< $30{\mu}g/kg$ DM) and liver (< $100{\mu}g/kg$ wet weight) indicated that productivity of the sheep may be reduced by a deficiency of this element. On one farm copper concentrations in the lever were in the liver were in the deficient range (< $5{\mu}g/kg$ wet weight) for part of the year. It is likely that this is a result of high intakes of iron from pasture (up to 4.5 g Fe/kg DM) and soil, as indicated by high concentrations of iron in faeces (up to 7 g Fe/kg DM). Molybdenum intake is unlikely to have had much influence on copper absorption because pasture concentrations of this element were not unusually high (1 to 5 mg/kg DM). Zinc in pastures on two farms was below 10 mg/kg DM for part of the year. On one of these farms, the concentration of zinc in faeces was below 30 mg/kg DM throughout the year and this is consistent with zinc intakes of 7 to 15 mg/kg. Despite these low intakes, the concentratons of zinc in plasma were consistently above deficient levels. No clinical signs of deficiencies of any of the elements studied were observed.