A molybdenum–sulfur–cadmium interaction in sheep

Abstract

We determined the effects of increased dietary concentrations of molybdenum and sulfur on the accumulation and tissue concentrations of cadmium in sheep, and compared them with effects on copper. Forty sheep, each weighing approximately 40 kg, were adjusted for 3 weeks to a basal diet of 80% wheaten chaff and 20% lupin seed containing (per kg dry weight) 0·016 mg Cd, 0·45 mg Mo, 3·4 mg Cu, and 1·9 g S. On Day 0 of treatment, 8 sheep were killed and the tissues analysed for trace minerals to provide a baseline value. The remaining sheep were divided into 4 dietary treatment groups: control (basal diet plus 4 mg Cd/kg), +Mo (control diet plus 15 mg Mo/kg), +S (control diet plus 4 g S/kg), +Mo+S (control diet+15 mg Mo+4 g S/kg).

The treatment period lasted 80 days, after which sheep were killed for tissue samples. Sulfur alone reduced the accumulation of Cd in liver, kidney, and muscle by 60% compared with control sheep (P < 0·05). Molybdenum alone reduced Cd accumulation by 40% in liver and muscle (P < 0·05) and 30% in kidney (P = 0·09). When provided together (+Mo+S), the effect was equivalent to feeding with Mo alone, showing that Mo blocked the effect of S. Cadmium concentrations in whole kidneys for the 4 respective treatments were 6·40 ± 0· 7, 2·8 ± 0·3, 4·5 ± 0·8, and 5·0 ± 0·5 mg/kg fresh weight. The pre-treatment concentration was 0·7 ± 0·2 mg/kg.

For Cu in blood and tissues, the effects of Mo and S treatment were consistent with the thiomolybdate hypothesis, and were quite different from those seen for Cd. Copper concentrations in whole kidney for the 4 treatments were 4·1 ± 0·1, 3·5 ± 0·2, 4·7 ± 0·3, and 22·4 ± 3·9 mg/kg fresh weight. The pre-treatment concentration was 4·1 ± 0·3 mg/kg. The results show that increased dietary levels of Mo and S reduce the accumulation of Cd in tissues, and the mechanisms of action differ from those involving Cu.