A split-herd, randomised mineral-vitamin supplementation experiment was carried out in a large, trace element deficient dairy herd over two years. Ten weeks before the herd's mean calving date, 147 Holstein-Friesian cows were fed grass silage on to which 50 g per head of a mineral-vitamin supplement (3000 mg copper, 500 mg iodine, 45 mg selenium and 80 mg cobalt per kg of supplement as specified) was sprinkled twice daily and 147 cows were fed the silage alone until calving. The supplement had no effect on the incidence of abortion (1.4 per cent), dystocia (2.3 per cent), fetal maldisposition (7.3 per cent), perinatal mortality (6.0 per cent) or retained fetal membranes (4.0 per cent), but it significantly increased the concentrations of trace elements in the blood and tissues of dead perinatal calves from 10 supplemented dams compared with those from eight unsupplemented dams. It also significantly increased the concentrations of trace elements in the blood of the cows and newborn calves in the supplemented group.
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