THE EFFECTS OF SULPHATE REMOVAL FROM THE DRINKING WATER ON THE PLASMA AND LIVER COPPER AND ZINC CONCENTRATIONS OF BEEF COWS AND THEIR CALVES

Pregnant Hereford cows (n = 99) and heifers (n = 98) whose ration contained 10 mg Cu kg−1 DM and 20 mg Zn kg−1 DM were assigned to two treatments. The water supply (sulphated water) for one group contained 500 mg S L−1 as sulphates. The sulphates in the water (desulphated) for the other group had been decreased to 42 mg S L−1 by reverse osmosis. Changes in plasma and liver copper and zinc concentrations were monitored in the cows and their calves during the winter drylot and pasture periods. The initial plasma and liver copper concentrations in all cows indicated a deficient status. At calving, the plasma copper concentration had declined in both groups. The greatest decrease was evident in the cows on sulphated water. At calving, the liver copper concentration had declined in both water treatment groups but was lowest in the cattle on the sulphated water. After calving, plasma and liver copper concentrations in both groups increased; this increase was greatest in the cows drinking the desulphated water. Water treatment had no effect on the copper status of the nursing calves. Water purification had a positive effect on the body weights of first and second calf heifers. Although the zinc status was normal, the plasma zinc declined and liver zinc increased in the cows at calving. These changes were independent of water treatment. When the sulphur in the drinking water was decreased to 42 mg L−1 by reverse osmosis there was a positive effect on the copper status of beef cows. Further research is required into higher dietary copper intakes, as 10 mg Cu kg−1 DM was not adequate in improving the deficient copper status of these cattle. Key words: Water sulphates, copper, zinc, beef cattle