Clinically silent hypocuprosis and the effect of molybdenum loading on beef calves in Gippsland, Victoria

Abstract

Whole blood and liver copper concentrations of less than 0.5 µg per ml and 6 p.p.m. dry weight respectively were found in healthy beef calves from an acid soil region at Koonwarra in Victoria. Pasture samples collected each month for a year contained 2.4–6.7 p.p.m. dry weight of copper, 2.1–9.2 p.p.m, dry weight of molybdenum, and 0.07–0.47% dry weight of sulphate. The copper/molybdenum ratio was usually well below 2.0.Changes in the copper status of the cattle were related to seasonal fluctuations in the copper and molybdenum contents of the pastures. A macrocytic hypochromic anaemia was found in hypocuprotic calves. However, pallor of the mucous membranes was not observed and there was no relationship between coat colour and copper concentration of either hair or whole blood. The subcutaneous injection of 120 mg copper as glycinate raised the concentration of copper in the whole blood and liver of calves to c. 0.8 µg/ml and up to 50 p.p.m. dry weight respectively. Growth rates of calves given copper improved significantly and their carcass weights were 8.4% heavier than controls. In this environment the effects of a single treatment with copper glycinate lasted only 5 months. Although liver copper contents ranged from below 5 to above 70 p.p.m. dry weight, the copper contents of other tissues examined, such as kidney, spleen, heart, and bones, were similar whether the animals had received additional copper or molybdenum or neither. At the levels of molybdenum found in the pastures (2–9 p.p.m. dry weight) the synthesis of ceruloplasmin was readily decreased, whereas erythrocyte copper decreased more slowly. Therefore the estimation of ceruloplasmin oxidase activity in plasma is suggested as a reliable and convenient means of assessing bovine hypocuprosis. The regression analyses showed a strongly positive correlation (r = 0.97) of plasma copper with ceruloplasmin oxidase activity as determined with p-phenylenediamine as substrate at the optimal pH. Special molybdenum pellets given to the calves augmented the tissue levels of molybdenum tenfold, but copper depletion did not occur to the point where clinical signs of copper deficiency or of molybdenosis appeared. In contrast to calves with large copper reserves, the mitochondria1 fraction of liver cells from hypocuprotic calves was found to contain more and the microsomal fraction less of the total liver copper. Because of the complex relationships between soil, pasture, and animals, it is concluded that a general recommendation for the minimum copper requirement of grazing cattle cannot reasonably be made without reference to soil and pasture concentrations of copper, molybdenum, and sulphate.