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Amino acid δ15N values predict body condition status in a captive population of muskoxen

Savory, Garrett1; Cook, Molly1; Breed, Greg1; Blake, John1; O'Brien, Diane1

Published Sep 28, 2026 on Dryad. https://doi.org/10.5061/dryad.rv15dv4pp

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Abstract

Measures of body condition, particularly protein balance, are important in understanding the health of wildlife populations but can be difficult or impossible to obtain from free-living animals. One potential biomarker, the δ15N value of bulk tissue, has had mixed success in predicting body condition. δ15N values of amino acids (AAs) have been shown to be more sensitive measures of trophic position than the bulk δ15N value and may also be more sensitive to changes in body condition. Here we evaluate AA δ15N values as a method to assess body condition using archived serum samples from a captive population of muskoxen (Ovibos moschatus) that had decreased mass resulting from feed that inadvertently provided marginal to deficient levels of several dietary trace elements. We predicted that AA δ15N values would be associated with deviations from expected body mass, and they would be more sensitive than bulk δ15N values. We evaluated several linear mixed-effect models with δ15N values of bulk serum, AAs, and other variables. In females, the δ15N values of glutamate/glutamine, leucine, aspartate/asparagine, and serine, plus pregnancy status, best predicted difference from expected mass; in males, the δ15N values of glutamate/glutamine, leucine, and proline best predicted difference from expected mass. Bulk δ15N values were not associated with the difference from expected mass. δ15N values of AAs have potential as a tool for researchers to evaluate body condition in animals.