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Trace Metal and Mineral Composition of Milk and Blood from Goats Fed Silage Produced on Sludge-Amended Soil¹

ABSTRACT

The transfer of heavy metals from sewage sludge into the food and feed chain is a significant concern to the health of humans and animals. We measured the accumulation of trace metals in the milk and blood of dairy goats (Capra hircus) fed corn (Zea mays L.) silage grown on sludge-amended vs. conventionally fertilized soil for 3 consecutive years. The silage contained levels of Cd up to 5.3 mg/kg. Zinc, the only other sludge-borne metal that was accumulated by corn, was accumulated to a lesser extent than Cd, which resulted in low Zn/Cd ratios.

The Cd concentrations of goat milk were not increased, even though the animals received as much as 5 mg Cd each day from corn silage containing high levels of bioaccumulated Cd.

Zinc levels in milk decreased as the amount of silage-borne Zn increased within the three treatments fertilized with sludge, but no differences were noted when the control treatment was contrasted with all sludge treatments. Goat's milk from animals on the control treatment contained higher levels of Cu than milk from animals of the various sludge-fertilized treatments. The higher levels of Cd in silage from the sludge-amended treatments may have limited Cu absorption by the animals.

The elemental concentrations of 14 other metals and minerals in milk were not affected by treatment nor time within the lactation period. Although colostrum generally contained higher concentrations of most minerals, no treatment effect was observed. As was true with milk composition, Cu was the only element in blood that was consistently affected by treatment. Copper levels in blood were higher for animals of the control treatment, even though all animals received a Cu-containing trace mineralized salt ad libitnm.

Key Words: cadmium • zinc • copper • heavy metals

¹ Contribution from the Soil & Water Management Research Unit, USDA-ARS and the Minnesota Agric. Exp. Stn., Paper no. 13 161, Scientific Journal Series. Appreciation is expressed to the U.S. Environmental Protection Agency, Cincinnati, Ohio, for partial support of this research.

² Research Soil Scientist, USDA-ARS, and Professor, Univ. of Minnesota, St. Paul; Research Asst., Animal Sci. Dep., Univ. of Minnesota; and Professor and Head, Dep. of Animal Sci., Univ. of Minnesota, St. Paul, MN 55108, respectively.

Received for publication November 4, 1982.