Experimentally induced chronic copper toxicity in cattle.

Eight Bonsmara bulls and eight Bonsmara heifers, having masses of between 210 and 266 kg when selected, were randomly allocated to four groups, each comprising two bulls and two heifers. Group 1 received 0.6 mg of copper (Cu)/kg of body mass per day (bm/d), group 2, 10 mg of Cu/kg of bm/d and group 3, 20 mg of Cu/kg of bm/d as a copper sulphate solution, given orally, 5 d a week over 745 d. Group 4 was the control group. One bull from group 3 was euthanased on day 679 of the trial, a heifer from group 3 and a bull from group 2, on day 695 of the trial, and a heifer from group 2, on day 731 of the trial, after they had shown clinical signs. During the course of the trial, clinical signs, serum gamma glutamyltransferase and aspartate aminotransferase activity, blood urea nitrogen, and plasma copper, zinc and iron concentrations were monitored. Live mass was recorded weekly to determine any effect on mass gain. The liver and kidney copper, zinc, iron and managanese concentrations at the time of death or slaughter are given. From the results it was concluded that subclinical damage to the liver and eventual copper toxicity can occur when cattle are continually exposed to oral doses > or = 12 mg of Cu/kg of bm/d. It was also concluded that cattle can probably tolerate oral doses of < or = 0.6 mg of Cu/kg of bm/d for an indefinite period, provided there are no other sources of copper, such as may occur with air-pollution, or provided no other adverse mineral interactions occur, such as may occur with molybdenum deficiency.