THE RELATIVE ACCUMULATION OF COPPER IN THE LIVER AND KIDNEYS OF SHEEP FED CORN SILAGE SUPPLEMENTED WITH COPPER CHLORIDE, COPPER ACETATE OR COPPER SULPHATE

Abstract

Thirty-two crossbred wethers were used in a randomized block design to study the relative solubility of copper (Cu) in rumen contents and its accumulation in liver and kidneys when fed as three Cu salts, chloride, acetate and sulphate. Cu was added to a corn silage-based diet (containing 6.7 mg Cu kg−1 dry matter (DM)) at a rate of 29 mg Cu kg−1 DM to give a final Cu concentration of 35.7 mg Cu kg−1 DM during an 87-d feeding experiment. Eight sheep were slaughtered at the start of the experiment and the remainder divided between four treatments: control, copper chloride, copper acetate and copper sulphate. Blood samples were taken every 28 d and liver, kidney and rumen content samples taken at slaughter, at the end of the experiment. Liver Cu concentration (mg kg−1 DM) increased from an initial value of 569 to 1174, 1038 and 1050 in the chloride, acetate and sulphate treatments, respectively, and decreased to 512 in the control over 87 d. In the Cu-supplemented wethers, the Cu retained in the liver represented between 1.9 and 2.5% of the Cu ingested. Kidney Cu concentration (mg kg−1 DM) increased from 16 to 114, 59 and 23 in the chloride, acetate and sulphate treatments, respectively, but remained constant in the control. Plasma Cu concentration decreased (P < 0.001) throughout the experiment with the control and sulphate treatments, and remained constant with the chloride and acetate treatments. Plasma ceruloplasmin activity decreased in the control wethers, but remained constant in the other three treatments. Plasma aspartate aminotransferase and diethyl-succinate carboxylesterase activities increased (P < 0.05 and P < 0.01, respectively) in the chloride treatment compared with the acetate and sulphate treatments. The solubility of Cu in rumen contents was 11.1, 13.0, 15.1 and 15.7% in wethers fed the chloride, control, sulphate and acetate diets, respectively. However, the only significant difference occurred between the chloride and acetate groups (P < 0.05). It was concluded that the high dietary levels of copper chloride, acetate or sulphate were equally effective at increasing liver and kidney Cu concentrations in normocupraemic sheep to levels encountered at the haemolytic stage of chronic copper poisoning. Key words: Sheep, copper chloride, copper acetate, copper sulphate, toxicity