Trace element nutrition of grazing ruminants. 1. Degree of oxidation, diet, frequency of dosing and location in the gastro-intestinal tract as factors affecting the ability of oxidized copper wire to promote hepatic copper storage

Abstract

Factors affecting the ability of oxidized copper (Cu) wire to promote hepatic Cu storage in penned and grazing sheep were examined in two experiments. The incorporation of molybdenum (Mo) and sulfur (S) into the diet did not reduce hepatic Cu storage, but storage was negligible when elemental Cu was used as the supplement, and it is suggested that dose rates could be manipulated by varying the extent of oxidation of the particles. Oxidized particles were relatively ineffective when held in the rumen in a nylon bag, and some of the variability in the pattern of hepatic Cu storage after dosing is likely to be associated with the rate of clearance of the particles from the rumen; there was no evidence that particles were rendered ineffective by being held in the rumen for up to 6 weeks. Excessive hepatic Cu concentrations were observed in some sheep and were attributed to the quantity of supplement given, the high Cu content of the basal diets, and to the failure to scale the dose in proportion to liver weight or liveweight. Dosing at 6-monthly intervals reduced variability in hepatic Cu concentration through time, but the strategy may lead to unacceptable hepatic Cu concentrations unless dose rates or the extent of oxidation of the particles are appropriately reduced.