Retention by sheep of copper from aerobic digests of pig faecal slurry

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Abstract
SUMMARY Dried grass originating from a farm on which herbage had been repeatedly dressed with faecal slurry from pigs given diets containing 250 mg copper/kg had a very variable, but frequently high content of copper. A maximum content of 70 mg Cu/kg dry matter was found. The mean copper content of growing herbage sampled subsequent to this finding was 10·5 mg/kg, while residues of slurry on the soil surface contained 805 mg Cu/kg. In an experiment involving three groups of eight sheep the utilization and hepatic retention of copper from the solid residues of an aerobic digest of high-copper faecal slurry from pigs was investigated. When these residues constituted 1 or 2% of the dietary dry-matter intake of copper-deficient sheep, rapid increases in plasma copper content, in plasma ferroxidase I activity and in hepatic copper content occurred. Thus copper from this source was readily utilized and retained. The utilization of copper added to the diet as cupric sulphate was compared with that of copper from dried slurry solids in an experiment with two groups of four sheep. Although the rate of recovery of plasma copper and ferroxidase I activity tended to be slower in sheep given slurry solids this difference was not statistically significant. A significantly slower rate of increase in hepatic copper content resulted from the ingestion of slurry solids. The significance of these findings is discussed with particular respect to the inadvertent ingestion of residues from the soil surface of pastures dressed with slurry and from the variable inclusion of such residues in herbage uplifted during forage harvesting.

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