Two groups of newly weaned sheep were grazed for 12 months on pasture which for one group provided less than 1 p.p.m. molybdenum, and for the other 8 p.p.m. molybdenum. Copper content was around 7 p.p.m. and inorganic sulphate content averaged 0.4 for the first 7 months and 0.2 for the last 5 months. There was no adverse effect on growth or haematology from the high molybdenum. In conjunction with high molybdemun, the higher inorganic sulphate nrevented copper storage, but copper storage did occur when inorganic sulphate was at the lower level. Molybdenum appeared in the blood at lower but not at the higher level of inorganic sulphate. High molybdenum in the diet caused accumulation of molybdenum in bones. kidney, and spleen. It is concluded that high molybdenum in the diet is not itself toxic and that it is harmful to sheep only when there is also present sufficient inorganic sulphate and a low enough dietary copper for copper depletion and copper deficiency symptoms to occur.
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