The effect of disposing high rates of copper-rich pig slurry on grassland on the health of grazing sheep

Abstract

SummaryOver a 3-year period 900 m3/ha of copper-rich pig slurry were spread during the growing season on a 0·6 ha permanent grassland sward and the grass continually grazed off each season with the same sheep. A total of 47 kg Cu/ha were applied to the area and this increased the EDTA-extractable copper in the topsoil. Herbage copper concentrations clearly showed that sheep grazing the area were continually exposed to high concentrations, and that most of the copper was present as surface contamination. Large quantities of copper were excreted in the sheep faeces indicating that copper passed through the animal.Monthly blood samples from the sheep showed that the enzyme glutamic-oxaloacetic transaminase (GOT) concentrations were slightly higher than those in sheep grazing an area which received no copper over the same period. By the end of the second season (October 1971) over 2000 i.u. GOT/1 were recorded in some sheep grazing the slurry treated area indicating severe liver breakdown at that time. However, during the winter when the sheep were inwintered, serum GOT concentrations decreased considerably. In the final grazing season a 0·2 ha area received monthly applications of copper sulphate instead of slurry. All sheep were slaughtered in November 1972 for post-mortem examination. There was little difference in the copper concentrations in the liver and kidneys of the sheep grazing the control and the slurry areas, although the sheep which grazed the copper sulphate area in the final season had higher concentrations.As no sheep died from chronic copper poisoning during the course of the investigation there would appear to be little or no danger to the health of sheep from grazing land which is receiving pig slurry at rates which supply less than 16 kg Cu/ha/year.