Influence of age and production type on liver copper concentrations in calves

A retrospective study of necropsy reports was undertaken to assess the relation between liver copper concentration and age, sex, and production class for calves that did not have a history compatible with copper toxicosis or with copper deficiency. Results of a generalized least squares regression analysis of 601 records found that copper concentration was as much as 60 mg/kg wet weight higher for dairy calves than for beef calves (P < 0.00001, R2 = 0.172). For both beef and dairy calves, copper concentration also was significantly associated with linear (P = 0.001) and nonlinear (age2, P = 0.002; age3, P = 0.008) functions of age, where the concentration increased for the first 2 months, then declined until 9 months of age, after which it began to increase. Sex was not associated with copper concentration (P = 0.22). The 95% confidence intervals of the mean concentration for a group of calves and the 95% prediction intervals of a single concentration value for an individual animal are presented. As a consequence of the significant influence of both production class (dairy or beef) and age on liver copper concentration of calves with no evidence of copper toxicosis or copper deficiency, diagnosis of copper imbalances based on liver copper concentration in calves should consider the diagnostic covariates of age and production class.