The clinical significance of measuring copper concentration in blood plasma of Dutch sheep
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For blood plasma copper concentrations in Dutch sheep, reference values, clinical cut-off values, seasonal variation and within flock variation are partly unknown. To determine the clinical significance of blood plasma copper concentration in sheep, a study was conducted with the aims (1) to determine the reference values for copper concentrations in blood plasma, (2) quantify the difference in copper concentrations between sheep suspected of mineral disbalance and sheep unsuspected of mineral disbalance and identify clinical cut-off values for copper intoxication or deficiency, (3) describe the seasonal variation of copper concentrations, and (4) describe the variation in copper values within Dutch sheep flocks. In this cross-sectional study, 1,698 blood plasma samples of Dutch sheep were obtained through convenience sampling, of which 1,270 samples were sent in with a suspicion of a mineral disbalance. The samples were sent in between 1999 and 2012. A mixture model was used to determine clinical cut-off values. The 95 % reference interval for copper concentration in blood plasma of Dutch sheep in this study was 3.6 µmol/L – 21 µmol/L. Sheep suspected of a mineral disbalance had significantly higher copper values in blood plasma than sheep unsuspected of a mineral disbalance. In April and June, significantly higher copper values in blood plasma were found compared to the other months of the year (p < 0.05). The within-farm variation in copper values was greater than 10.0 µmol/L. No clinical cut-off values could be obtained through the mixture model. Altogether, these findings suggest there is some value in measuring the copper concentration in sheep, but when interpreting these results, season should be taken into account, and multiple samples should be taken within a flock in order to validly assess the copper status of the flock as a whole.