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Sources: Kabata-Pendias, A. and Pendias, H., Trace Elements in Soils and Plants, CRC Press, Boca Raton, FL, 1984; Edwards, D.R. and Daniels, T.C., Bioresour. Technol., 41, 9, 1992; Arora, C.L. et al., Indian J. Agric. Sci., 45, 80, 1975; Adriano, D.C., Trace Elements in the Terrestrial Environment. Springer-Verlag, Berlin, 1986.

Sources: Kabata-Pendias, A. and Pendias, H., Trace Elements in Soils and Plants, CRC Press, Boca Raton, FL, 1984; Edwards, D.R. and Daniels, T.C., Bioresour. Technol., 41, 9, 1992; Arora, C.L. et al., Indian J. Agric. Sci., 45, 80, 1975; Adriano, D.C., Trace Elements in the Terrestrial Environment. Springer-Verlag, Berlin, 1986.

to 20 mg/kg and from 250 to 100 mg/kg, respectively. Spears et al. [44] evaluated the effects of lowering Cu and Zn supplementation from 15 to 5 mg/kg and from 100 to 25 mg/kg, respectively, on trace metal concentrations in swine feces. Results demonstrated that lower Cu and Zn concentrations in dietary intake reduced Cu and Zn excretions in feces by 40% without negatively affecting carcass characteristics or carcass value. Van Heugten et al. [8] demonstrated similar results. Reducing trace metal intake by animals is a possibility, but the lack of relevant information on possible health side-effects (e.g., impairment of immune system [45]) could limit acceptance of this practice.

Not all of the trace metals consumed by animals are absorbed by the animal's digestive tract; consequently, the manure is often trace metal enriched (Table 33.3). For example, swine can excrete approximately 80 to 95% of the total daily Cu and Zn contained in dietary supplements [19,42,46]. Kunkle et al. [9] found that Cu concentrations in poultry litter were linearly related to that in feed and that the litter Cu concentration was about 3.25-fold higher than values measured in the feed. Edwards and Daniels [47] reported that poultry manures were enriched in trace metals like Mn, Fe, Cu, and Zn. From numerous poultry manure compositional investigations, they summarized that the mean Mn, Fe, Cu, and Zn concentrations were 304, 320, 53, and 354 mg/kg, respectively [47]. Barker and Zublena [48] conducted a Cu and Zn concentration assessment in swine manure measured from several swine operations in North Carolina and reported that the mean concentrations were 15 and 62 mg/kg, respectively. These results suggest that animal manures are a significant source of several trace metals and that lack of ruminant assimilation and subsequent deposition of excreta in fields allows these trace metals to accumulate in soils.

Trace metal concentrations in animal manures vary greatly (Table 33.3). This should not be unexpected, considering the large number of management variables associated with manure management systems [49,50]. As shown in Table 33.5, trace metal concentrations like Cu, Fe, Mn, and Zn will vary depending upon source (broiler cake vs. poultry litter vs. feed). The large variation in trace metal concentration is probably a result of animal age, type of feed source, trace metal supplements, bedding differences, and manure storage practices [40]. Because of this large variation in trace metal concentrations, it is difficult to imply that manures from certain livestock types will have a specific trace metal compositional signature.

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