Direct and Indirect Linkages Between Trace Element Status and Health Indicators - a Multi-tissue Case-Study of Two Deer Species in Denmark

Measuring trace element concentrations in tissue can be a valuable approach to monitor animal health status. Temporal variation in the absorption, transport, and storage of elements between different tissues can, however, complicate the assessment of element-health relationships. Here, we measured concentrations of selected essential (copper (Cu), zinc (Zn), selenium (Se)) and non-essential (arsenic (As), cadmium (Cd), lead (Pb)) trace elements within blood, liver, kidney, and hair of fallow deer (Dama dama; N=20) and red deer (Cervus elaphus; N=21). Using multivariate regression and structural equation models, we estimated direct and indirect linkages between tissue-specific trace element profiles and long- (body condition) and short-term (serum protein biomarkers for acute inflammation, infection, and malnutrition) health indicators. Trace element concentrations varied markedly and were weakly correlated among tissues, with the exception of Se. After accounting for sex- and site-differences in trace element concentrations, body condition of red deer was directly, and positively, associated to trace element status in liver and hair, but not in kidney. For both deer species, trace element status in blood was directly linked to serum protein status with an indirect positive association to deer body condition. For fallow deer, no direct association between trace element status and body condition was detected in any of the tissues, possibly because of elemental homeostasis, and because all individuals were in good clinical health. This study shows that hair can serve as an effective, non-invasive, biomarker in deer health assessments, yet, to fully uncover trace element-health relationships a variety of sample matrices is preferred. Supplementary Information The online version contains supplementary material available at 10.1007/s12011-023-03926-3.

Table S3.Overview of the number of fallow deer (Dama dama; N=20) and red deer (Cervus elaphus; N=21) sampled across species, sex, age-class and study site during Nov-Dec 2021 in Denmark.

Figure S1 .
Figure S1.Boxplots showing the variation in trace element concentrations (μg g -1 w.w.) across study sites (top panel), sexes (middle panel), and age-classes (lower panel) measured in red deer (Cervus elaphus) tissue samples (N=21) collected during Nov-Dec 2021 in Denmark.Trace elements indicated with an asterisk (*) indicate a statistical difference (p<0.05) between groups while marginally significant differences (p<0.1) are marked with a dot ( • ) as determined with Kruskal-Wallis Rank Sum Test (3 group comparison) or the Mann-Whitney U test (2 group comparison).In all panels, the box shows the interquartile range of the data (25 th to 75 th percentile) with the median value indicated with a thick horizontal line.The whiskers represent the range of the data within 1.5 times of the interquartile range while outliers are plotted as individual points.Note that the y-axis is on the logarithmic scale.

Figure S2 .
Figure S2.Boxplots showing the variation in trace element concentrations (μg g -1 w.w.) across study sites (top panel), sexes (middle panel), and age-classes (lower panel) measured in fallow deer (Dama dama) tissue samples (N=20) collected during Nov-Dec 2021 in Denmark.Trace elements indicated with an asterisk (*) indicate a statistical difference (p<0.05) between groups while marginally significant differences (p<0.1) are marked with a dot ( • ) as determined with Kruskal-Wallis Rank Sum Test (3 group comparison) or the Mann-Whitney U test (2 group comparison).In all panels, the box shows the interquartile range of the data (25 th to 75 th percentile) with the median value indicated with a thick horizontal line.The whiskers represent the range of the data within 1.5 times of the interquartile range while outliers are plotted as individual points.Note that the y-axis is on the logarithmic scale.

Figure S3 .
Figure S3.Correlation plots showing the direction (red = positive, blue = negative) and strength of the correlations (rs values) in trace element concentrations among different tissue samples of red deer (Cervus elaphus, N=21) collected during Nov-Dec 2021 in Denmark.Tissue combinations marked with an asterisk (*) indicate a statistically significant correlation (p<0.05) for that element.

Figure S4 .
Figure S4.Correlation plots showing the direction (red = positive, blue = negative) and strength of the correlations (rs values) in trace element concentrations among different tissue samples of fallow deer (Dama dama, N=20) collected during Nov-Dec 2021 in Denmark.Tissue combinations marked with an asterisk (*) indicate a statistically significant correlation (p<0.05) for that element.

Figure S5 .
Figure S5.Plots showing the direction (red = positive, blue = negative) and strength of the correlations (rs values) in trace element concentrations within tissue samples (N=21) of red deer (Cervus elaphus) collected during Nov-Dec 2021 in Denmark.Element combinations marked with an asterisk (*) indicate a statistically significant correlation (p<0.05)within that tissue.

Figure S6 .
Figure S6.Plots showing the direction (red = positive, blue = negative) and strength of the correlations (rs values) in trace element concentrations within tissue samples (N=20) of fallow deer (Dama dama) collected during Nov-Dec 2021 in Denmark.Element combinations marked with an asterisk (*) indicate a statistically significant correlation (p<0.05)within that tissue.

Table S2 .
Overview of parameter values of the serum protein analyses for red deer (Cervus elaphus, N=21) and fallow deer (Dama dama, N=20) sampled during Nov-Dec 2021 in Denmark.

Table S4 .
Output of the structural equation models (SEMs) for red deer (Cervus elaphus, N=21) linking trace element status in different tissues (blood, liver, kidney, and hair) to multiple health indicators (BCS and Serum protein status).See main article for further details on SEM construction and meaning of variables.Model output forms the analytical basis for Fig.6in the main article.

Table S5 .
Output of the structural equation models (SEMs) for fallow deer (Dama dama, N=20) linking trace element status in different tissues (blood, liver, kidney, and hair) to multiple health indicators (BCS and Serum protein status).See main article for further details on SEM construction and meaning of variables.Model output forms the analytical basis for Fig.7in the main article.