Although it is well established that changes in dietary iron (Fe) intakes can influence copper (Cu) metabolism in animals, little attention has been paid to their importance in causing Cu deficiency in ruminants. The realization that silages frequently contain large amounts of Fe, mainly as a soil contaminant, prompted us to assess the potency of Fe as a Cu antagonist and to compare its effects with those of molybdenum (Mo).

In one experiment, 27 male Friesian calves, aged about 3 weeks, were allocated to three treatment groups and given a milk-substitute ration containing 2.5 mg Cu and 50, 250 or 500 mg Fe (as FeCl3.6H20)/kg DM. Liver biopsies were taken after 8 weeks and analyzed for Cu and Fe. As expected, tissue Fe increased by as much as 50% with increasing Fe intake. However, there were no effects of Fe on hepatic Cu retention in these pre-ruminant calves (liver Cu was 343, 372 and 390 mg/kg DM, respectively: SEM = 40).