Liver Mineral Levels Associated with Hoof Disease Occurrence and Severity in Roosevelt Elk (Cervus canadensis) in California, USA.

Trace minerals serve vital roles in physiologic functions of animals. In ungulates, trace minerals, including copper (Cu), selenium (Se), and zinc (Zn), are essential for immune function, as well as hoof development and maintenance. Trace minerals may influence the occurrence or severity of treponeme-associated hoof disease (TAHD), a debilitating infectious disease of free-ranging Roosevelt and Rocky Mountain ecotypes of elk (Cervus canadensis). To investigate associations between mineral levels and TAHD, we collected postmortem liver and hoof samples from free-ranging Roosevelt elk during TAHD surveillance from 2020 to 2021 in Del Norte and Humboldt counties, California, USA. We analyzed mineral levels in liver samples (n=81; 41 TAHD positive, 40 TAHD negative) to improve baseline information on the range of trace mineral concentrations for elk in the region. Hooves were examined for the presence of TAHD, and the severity of observed gross lesions was scored. Using the combined mineral and surveillance data, we constructed logistic and ordinal regression models to ask whether TAHD occurrence and TAHD lesion severity were associated with mineral concentrations, respectively. We did not find support for our hypothesis that lower mineral levels contributed to higher TAHD occurrence in the sample populations; however, Cu and Se in both TAHD-affected and unaffected elk were below previously reported reference ranges, so we cannot discount suboptimal levels of these minerals as potential risk factors for TAHD in elk in this region. Contrary to our hypothesis, higher Zn levels were correlated with TAHD occurrence and increasing lesion severity, which may be evidence of a host-mediated nutritional immune response to infectious disease. Further investigation is needed to understand regional variation in mineral levels and the impact on wildlife health before mineral supplementation can be recommended as an effective management tool.