Studies on the cause of a low copper status in cattle in south-eastern Queensland

Abstract

Four experiments were made to compare the copper/molybdenum/inorganic sulphate relationship in the diets of sheep and cattle and to determine if this relationship was responsible for the low copper status in cattle grazing pastures at the Animal Husbandry Research Farm at Rocklea, near Brisbane.
Experiment 1 measured changes in liver copper concentrations in four groups of two sheep on (1) a basal diet of oaten and lucerne chaff, (2) this diet supplemented with molybdenum,
(3) this diet supplemented with copper plus molybdenum, and (4) this diet supplemented with copper plus molybdenum plus inorganic sulphate. The findings confirmed that sheep can increase their liver copper reserves on a ration containing 2.5 p.p.m. Cu, that a high concentration of molybdenum (23 p.p.m. Mo) does not interfere with copper metabolism when the diet is low in inorganic sulphate (0.02 per cent.) and crude protein (4.4 per cent.) and that the addition of inorganic sulphate to provide 0.45 per cent. S04 permits the molybdenum to interfere with copper metabolism.
Experiment 2 was similar in design to Experiment 1 but included a comparison of sheep and cattle. The basal diet contained 9 per cent. linseed meal to give a productive ration of 8.2 per cent. crude protein. Findings were similar for sheep and cattle. Both species showed little decline in liver copper on a diet containing 4 p.p.m. Cu, 0.25 p.p.m. Mo and 0.02 per cent. S04 The addition of molybdenum to provide 11.5 p.p.m. Mo in this protein supplemented diet caused a marked fall in liver copper although the diet was low in inorganic sulphate. The further addition of inorganic sulphate as sodium sulphate to give 0.45 per cent. S04 caused an increased interference with copper metabolism.
Experiment 3 included a stall feeding treatment to examine the copper/molybdenum/sulphate relationship at the levels found in freshly cut pasture, a comparison of the changes in liver copper levels in cattle fed freshly cut pasture in stalls and in cattle grazing similar pasture, and a long-term experiment to determine changes in liver copper concentrations in cattle grazing these pastures over one year. Essential findings were (1) grazing cattle showed a marked fall in liver copper reserves th1·oughout the year, (2) this rate of decline in liver copper levels in grazing cattle was greater than in cattle stall-fed on freshly cut pasture and (3) inability to metabolize copper did not appear to be related either to the copper content or to the molybdenum level in these pastures.
Experiment 4 was firstly a measure of the rate of decline in liver copper levels in cattle grazing these pastures for 12 weeks up to the time at which the pasture was conserved as hay. The second stage was a stall-feeding experiment to examine the copper/molybdenum/sulphate relationship in a diet of pasture hay. Essential findings were (1) grazing cattle, as in Experiment 3, showed a marked fall in liver copper levels, (2) the decline in liver copper levels was greatest in animals during the grazing period, less in animals fed paspalum hay and least in animals fed a basal diet with a copper, molybdenum, inorganic sulphate and crude protein content similar to that of the paspalum hay and (3) as in Experiment 3 inability to metabolize copper could not be related either to the copper content or to the molybdenum level in these pastures.
From the findings of all four experiments the conclusion is drawn that the predominantly paspalum pasture at the Animal Husbandry Research Farm, Rocklea, contains some factor or factors, other than molybdenum in the presence of inorganic sulphate, which interfere with metabolism of copper by cattle.