Abstract. Determination of zinc concentrations in the liver of calves and young stock is commonly requested by practitioners and nutritionists to assess whether they receive an appropriate amount of zinc in their diet. However, interpretation of liver zinc concentrations is currently based on information reported for adult cattle for which the health status was unknown and irrespective of production class, sex, and age. A retrospective study of necropsy reports was undertaken to assess the relationships between liver zinc concentrations and age, sex, and production class for calves that did not have a history compatible with zinc toxicosis or zinc deficiency. Results of a generalized least squares, polynomial regression analysis of 474 records found that zinc concentration was not affected by sex (P ϭ 0.29) or production class (P ϭ 0.50). Zinc concentration was significantly associated with linear (P Ͻ 0.00001) and nonlinear (quadratic, P ϭ 0.0039) functions of age (r 2 ϭ 0.1503), where the concentration decreased from 93 mg/kg wet weight at 30 days of age to 57 mg/kg wet weight at 9 months of age, after which it began to increase. The age-specific 95% confidence limits of the mean concentration for a group of calves and the 95% prediction limits of a single concentration value for an individual animal estimated in this study suggest reconsideration of the recommended limits for liver zinc concentration in calves. As a consequence of the significant influence of age on liver zinc concentration of calves presumably not experiencing zinc toxicosis or deficiency, diagnosis of zinc imbalances based on liver zinc concentration needs to consider age as a diagnostic covariate.Zinc is essential for life as it is required for many physiological processes. Zinc is present in more than 300 metalloenzymes and is involved in DNA replication, RNA and protein synthesis, carbohydrate and lipid metabolism, gene expression, and appetite regulation. 1,16,20,37 Clinical manifestations of improper zinc status in cattle are severe. Zinc deficiency has been associated with poor production and growth, and a number of economically important health-related issues. 4,5,22,28,32,34 Clinical signs include poor body condition, dull appearance, decreased appetite, 9 rough hair coat, poor growth rates, impaired vision, diarrhea, hyperkeratosis, alopecia, 34 abortion, mummification, prolonged calving/uterine inertia, impaired vitamin A metabolism, immunosuppression, thymic hypoplasia/atrophy, marked decline in milk production and weight gain, reduction in circulating insulin and growth hormone levels, and decreased efficiency of feed use. 11,34 Although less common, zinc poisoning has also

Abstract.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 Ͻ 0.00001, R 2 ϭ 0.172). For both beef and dairy calves, copper concentration also was significantly associated with linear (P ϭ 0.001) and nonlinear (age 2 , P ϭ 0.002; age 3 , P ϭ 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 ϭ 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.