Relationship between the level of copper in the blood plasma and liver of cattle.

Nonlinear and linear least squares were used to determine the best fi t curve that would describe the relationship between blood plasma copper levels and liver copper levels in cattle. Data analyzed contained 540 paired blood and liver samples from grade Hereford calves, heifers and cows, and purebred Guernsey cows. The relationship between plasma and liver copper can be described by a constant for liver copper levels above 40 ppm dry weight. Depending upon procedure, the constants were .91, .92 and .91 /~g/ml of plasma copper. Although plasma copper levels for a given liver copper level below 40 ppm were highly variable, only 4% of the plasma levels below .5 /~g/ml had corresponding liver copper greater than 40 ppm. The difference in plasma copper levels between beef and dairy cows with liver Copper above 40 ppm was not statistically significant. Based on these data, plasma copper appears to be of little value in predicting liver copper. However, plasma copper levels of .5 /lg/ml or less are indicative of low liver copper levels. (