Associations between hair trace mineral concentrations and the occurrence of treponeme-associated hoof disease in elk (Cervus canadensis)

Abstract

Background: Trace minerals are important for animal health. Mineral deficiency or excess can negatively affect immune function, wound healing, and hoof health in domestic livestock, but normal concentrations and health impairment associated with mineral imbalances in wild animals are poorly understood. Treponeme-associated hoof disease (TAHD) is an emerging disease of free-ranging elk (Cervus canadensis) in the U.S. Pacific Northwest. Selenium and copper levels identified in a small number of elk from areas where TAHD is established (i.e., southwestern Washington) suggested a mineral deficiency may have increased susceptibility to TAHD. Our objectives were to determine trace mineral concentrations using hair from elk originating in TAHD affected areas of Washington, California, Idaho, and Oregon and assess their associations with the occurrence of the disease.

Results: We identified limited associations between TAHD occurrence and severity with hair mineral concentrations in 72 free-ranging elk, using Firth's logistic regression and multinomial regression models. We found consistent support for a priori hypotheses that selenium concentration, an important mineral for hoof health, is inversely associated with the occurrence of TAHD. Less consistent support was observed for effects of other minerals previously associated with hoof health (e.g., copper or zinc) or increased disease risk from potential toxicants.

Conclusion: Trace mineral analysis of hair is a non-invasive sampling technique that offers feasibility in storage and collection from live animals and carcasses. For some minerals, levels in hair correlate with visceral organs that are challenging to obtain. Our study using hair collected opportunistically from elk feet submitted for diagnostic investigations provides a modest reference of hair mineral levels in elk from the U.S. Pacific Northwest that may be useful in future determination of reference ranges. Although our results revealed high variability in mineral concentrations between elk, consistent relationship of possibly low selenium levels and TAHD suggest that further investigations are warranted.

Keywords: Cervus canadensis; Elk; hair; trace minerals; treponeme-associated hoof disease.

Fig. 1

Distributions of mineral concentrations and univariate odds ratios with respect to treponeme-associated hoof disease (TAHD) diagnosis. Split violin plots show distributions of mineral concentrations (μg/g) scaled specific to the 13 elements (panel labels) assessed in hair analyses in elk while overlaid colored points represent raw data for each disease status: TAHD negative (gray colors) and positive (red colors). Univariate logistic regressions generated simple odds ratios (OR) and 95% confidence intervals (CI) for minerals. Boxplots at the peaks of violin plots show the median and 25th and 75th interquartile ranges while black dots represent outliers. Of trace minerals relevant to hoof health, we noted two outlier values in selenium and cobalt. Arsenic, cadmium, cobalt, lead, and molybdenum values were below reporting limits; values shown are rescaled (see Methods: Data pre-processing section). Raw values for all minerals are in a data repository [23]

Fig. 2

Explanatory variable results from addressing five a priori hypotheses. Five panels show different models with visual summaries of explanatory variables’ estimates of odds ratios (black circles), 95% confidence intervals (bars), and presence of a statistically significant relationship (denoted by a star, ⋆) color-coded to represent different datasets: outliers removed (blue) or outliers included/full dataset (orange)