Analysis of the value of measurement of the activity of caeruloplasmin as an alternative to measurement of the concentration of elemental copper in plasma and serum of farmed red deer

Abstract

AIM: To evaluate the relationship between the concentration of elemental Cu and activity of caeruloplasmin (CP) in the plasma and serum of farmed red deer (Cervus elaphus).

METHODS: Paired serum and heparinised plasma samples taken from 142 deer from 10 herds in the North Island of New Zealand were tested for the concentration of elemental Cu and activity of CP. Additionally, liver biopsy samples were taken from 49 of the deer (all one herd). The relationship between individual results for the concentration of elemental Cu and activity of CP was examined using a segmented model, with random slope and intercept and threshold.

RESULTS: The activity of CP in plasma and that in serum were strongly correlated (R²=0.994), with a high level of agreement. The concentration of Cu and activity of CP also showed a strong association (R²>0.88 for both plasma and serum), although there were significant differences between herds, with the segmented regression model providing the best fit rather than a linear mixed model.

Using the current thresholds for elemental Cu, the relationship between the concentration of Cu and activity of CP suggested that an activity of CP of <4 IU/L indicates Cu deficiency, and that deer with an activity of CP of ≥7 IU/L have adequate Cu status.

CONCLUSIONS: The relationship between elemental Cu and CP is markedly different from the simple linear relationship previously reported for cattle. Above a threshold of 10 IU/L, the rise in elemental Cu per unit increase in activity of CP was 50% of that below 10 IU/L. This is probably because above this threshold the oxidative activity of CP per enzyme unit was greater.

CLINICAL RELEVANCE: The association between concentration of Cu and activity of CP was robust enough to define provisional thresholds for determining Cu status. However, the proximity of the deficiency threshold to the limit of detection of the CP test, the effect of herd on the association, and the inherent disadvantages of using an enzymatic system, mean that activity of CP should not be used routinely to estimate Cu status in deer. When assessing the Cu status of deer based on blood samples, the concentration of Cu in plasma or serum should be used.

KEY WORDS:

• Copper
• deer
• plasma
• serum
• caeruloplasmin
• Cu

Acknowledgements

The assistance of the Deer Research Group at Massey University is gratefully acknowledged, particularly Peter Wilson and Kathryn Goodwin-Ray, as is the support and assistance of the staff at New Zealand Veterinary Pathology, Hamilton and Palmerston North. The authors would also like to thank Geoff Jones for statistical support and advice. This project was financially supported by the Lewis-Fitch fund.