Liver copper concentration in cattle and herbage copper, sulphur, iron and molybdenum concentrations on commercial farms in the Wairoa region

Seasonal changes in herbage elements (Cu, Mo, S, Fe), pasture growth, and soil moisture were measured and their relationships with liver Cu concentration in weaner heifers (n=10–12) and breeding cows (n=10–12) were determined on 7 commercial farms in the Wairoa region. Liver biopsy samples were collected at 2 to 4 monthly intervals and herbage and soil moisture monthly from spring 1996 to spring 1998. Mean Mo concentration of herbage offered to cattle on the 7 farms ranged from 0.7 to 3.2 mg Mo/kgDM and Cu herbage concentrations from 5.7 to 10.5 mg Cu/kgDM. Mean concentrations of Cu in cattle livers ranged from 85 to 204 μmol Cu/kgFW across farms. Herbage Cu, S and Fe concentrations were highly seasonal with low levels in late spring– summer and high levels in autumn and winter. In contrast, herbage Mo was less seasonal. There was a suggestion that variation in liver Cu across seasons was positively affected by increasing herbage Cu concentration and negatively affected by increasing herbage S concentration and unaffected by herbage Mo concentration. Over the two years 46% of nonCu supplemented cows and 32% of weaners had deficient (<95 μmol Cu/kgFW) liver Cu levels but clinical signs of Cu deficiency were not observed. Weaner liver Cu concentrations were low in summer and autumn (126 μmol/kgFW) but repleted over the winter and spring seasons (195 and 237 μmol/kgFW respectively). Cows had highest levels of liver Cu in summer (147 μmol/kgFW) but these fell steadily over winter to reach low (62 μmol Cu/ kgFW) levels in spring before calving. The study supports the conclusion of Korte (1995) that in the Wairoa region herbage Mo may impair absorption of Cu in cattle grazing pasture with Mo levels as low as 0.5 mg/kgDM, but once herbage Mo rises above 2 mg/kgDM then further reduction in Cu absorption is minimal.